Metabolic predictors of weight gain

Relation Between Obesity and Type 2 Diabetes: Evolutionary Insights, Perspectives and Controversies

PURPOSE OF REVIEW

Since the mid-twentieth century, obesity and its related comorbidities, notably insulin resistance (IR) and type 2 diabetes (T2D), have surged. Nevertheless, their underlying mechanisms remain elusive. Evolutionary medicine (EM) sheds light on these issues by examining how evolutionary processes shape traits and diseases, offering insights for medical practice. This review summarizes the pathogenesis and genetics of obesity-related IR and T2D. Subsequently, delving into their evolutionary connections. Addressing limitations and proposing future research directions aims to enhance our understanding of these conditions, paving the way for improved treatments and prevention strategies.

RECENT FINDINGS

Several evolutionary hypotheses have been proposed to unmask the origin of obesity-related IR and T2D, e.g., the "thrifty genotype" hypothesis suggests that certain "thrifty genes" that helped hunter-gatherer populations efficiently store energy as fat during feast-famine cycles are now maladaptive in our modern obesogenic environment. The "drifty genotype" theory suggests that if thrifty genes were advantageous, they would have spread widely, but proposes genetic drift instead. The "behavioral switch" and "carnivore connection" hypotheses propose insulin resistance as an adaptation for a brain-dependent, low-carbohydrate lifestyle. The thrifty phenotype theory suggests various metabolic outcomes shaped by genes and environment during development. However, the majority of these hypotheses lack experimental validation. Understanding why ancestral advantages now predispose us to diseases may aid in drug development and prevention of disease. EM helps us to understand the evolutionary relation between obesity-related IR and T2D. But still gaps and contradictions persist. Further interdisciplinary research is required to elucidate complete mechanisms.

Temporal trends, in-hospital outcomes, and risk factors of acute myocardial infarction among patients with epilepsy in the United States: a retrospective national database analysis from 2008 to 2017

Background

The relationship between epilepsy and risk of acute myocardial infarction (AMI) is not fully understood. Evidence from the Stockholm Heart Study indicates that the risk of AMI is increased in people with epilepsy. This study aims to analyze the temporal trends in prevalence, adverse clinical outcomes, and risk factors of AMI in patients with epilepsy (PWE).

Methods

Patients aged 18 years or older, diagnosed with epilepsy with or without AMI and hospitalized from January 1, 2008, to December 31, 2017, were identified from the National Inpatient Sample (NIS) database. The Cochran-Armitage trend test and logistic regressions were conducted using SAS 9.4. Odds ratios (ORs) were generated for multiple variables.

Results

A total of 8,456,098 inpatients were eligible for our analysis, including 181,826 comorbid with AMI (2.15%). The prevalence of AMI diagnosis in PWE significantly increased from 1,911.7 per 100,000 hospitalizations in 2008 to 2,529.5 per 100,000 hospitalizations in 2017 (Ptrend  < 0.001). Inpatient mortality was significantly higher in epilepsy patients with AMI compared to those without AMI (OR = 4.61, 95% CI: 4.54 to 4.69). Factors significantly associated with AMI in PWE included age (≥75 years old vs. 18 ~ 44 years old, OR = 3.54, 95% CI: 3.45 to 3.62), atherosclerosis (OR = 4.44, 95% CI: 4.40 to 4.49), conduction disorders (OR = 2.21, 95% CI: 2.17 to 2.26), cardiomyopathy (OR = 2.11, 95% CI: 2.08 to 2.15), coagulopathy (OR = 1.52, 95% CI: 1.49 to 1.54), dyslipidemia (OR = 1.26, 95% CI: 1.24 to 1.27), peptic ulcer disease (OR = 1.23, 95% CI: 1.13 to 1.33), chronic kidney disease (OR = 1.23, 95% CI: 1.22 to 1.25), smoking (OR = 1.20, 95% CI: 1.18 to 1.21), and weight loss (OR = 1.20, 95% CI: 1.18 to 1.22).

Conclusion

The prevalence of AMI in PWE increased during the decade. Mortality rates were high among this population, highlighting the need for comprehensive attention to prophylaxis for risk factors and early diagnosis of AMI in PWE by physicians.

Patterns and Determinants of Weight Gain among People Who Use Drugs Undergoing Treatment for Recovery in Lebanon

Substance use disorder compromises the nutritional status and the eating habits of drug users, often leading to malnutrition. Once referred for treatment, hyperphagia and poor lifestyle practices leading to weight gain are observed. This study aimed to examine the patterns and extent of weight change as well as the determinants of weight gain in a sample of drug users who were receiving treatment in Lebanon. A total of 172 male participants undergoing either rehabilitation or opioid substitution treatment (OST) were included. Multivariate regression analysis was applied to assess the effect of different variables on weight gain while adjusting for potentially confounding variables. Approximately two-thirds (65.1%) of the participants gained weight (OST: 54.3%, rehabilitation: 78.2%; p < 0.05). The mean weight gain was 5.9 kg and was mainly reported among participants in the underweight, normal, and overweight pre-treatment categories and accentuated in the rehabilitation group (OST: 2 kg, Rehabilitation: 10.6 kg). Around half of the participants moved from the normal weight category to the overweight and obese categories during treatment. Weight gain was negatively associated with the number of previous treatment attempts (Odds Ratio = 0.86; Confidence Interval: 0.74-0.99), duration of current treatment (Odds Ratio = 0.98; Confidence Interval: 0.96-0.99), and pre-treatment body mass index (BMI) (Odds Ratio = 0.88; Confidence Interval: 0.80-0.96). Investigating other nutrition and lifestyle practices, neither nutrition knowledge, food addiction, physical activity level, nor sleep quality were associated with weight gain. Treatment through drug use was associated with meaningful weight gain that might lead to health risk factors. Developing health promotion programs is crucial to enhance treatment and decrease the risk of relapse.

Branched Chain Amino Acid Supplementation to a Hypocaloric Diet Does Not Affect Resting Metabolic Rate but Increases Postprandial Fat Oxidation Response in Overweight and Obese Adults after Weight Loss Intervention

Background: Branched chain amino acids (BCAA) supplementation is reported to aid in lean mass preservation, which may in turn minimize the reduction in resting metabolic rate (RMR) during weight loss. Our study aimed to examine the effect of BCAA supplementation to a hypocaloric diet on RMR and substrate utilization during a weight loss intervention. Methods: A total of 111 Chinese subjects comprising 55 males and 56 females aged 21 to 45 years old with BMI between 25 and 36 kg/m² were randomized into three hypocaloric diet groups: (1) standard-protein (14%) with placebo (CT), (2) standard-protein with BCAA, and (3) high-protein (27%) with placebo. Indirect calorimetry was used to measure RMR, carbohydrate, and fat oxidation before and after 16 weeks of dietary intervention. Results: RMR was reduced from 1600 ± 270 kcal/day to 1500 ± 264 kcal/day (p < 0.0005) after weight loss, but no significant differences in the change of RMR, respiratory quotient, and percentage of fat and carbohydrate oxidation were observed among the three diet groups. Subjects with BCAA supplementation had an increased postprandial fat (p = 0.021) and decreased postprandial carbohydrate (p = 0.044) oxidation responses compared to the CT group after dietary intervention. Conclusions: BCAA-supplemented standard-protein diet did not significantly attenuate reduction of RMR compared to standard-protein and high-protein diets. However, the postprandial fat oxidation response increased after BCAA-supplemented weight loss intervention.

Metabolic and cardiovascular adaptations to an 8-wk lifestyle weight loss intervention in younger and older obese men

The number of older obese adults is increasing worldwide. Whether obese adults show similar health benefits in response to lifestyle interventions at different ages is unknown. The study enrolled 25 obese men (body mass index: 31-39 kg/m²) in two arms according to age (30-40 and 60-70 yr old). Participants underwent an 8-wk intervention with moderate calorie restriction (∼20% below individual energy requirements) and supervised endurance training resulting in ∼5% weight loss. Body composition was measured using dual energy X-ray absorptiometry. Insulin sensitivity was assessed during a hypersinsulinemic-euglycemic clamp. Cardiometabolic profile was derived from blood parameters. Subcutaneous fat and vastus lateralis muscle biopsies were used for ex vivo analyses. Two-way repeated-measure ANOVA and linear mixed models were used to evaluate the response to lifestyle intervention and comparison between the two groups. Fat mass was decreased and bone mass was preserved in the two groups after intervention. Muscle mass decreased significantly in older obese men. Cardiovascular risk (Framingham risk score, plasma triglyceride, and cholesterol) and insulin sensitivity were greatly improved to a similar extent in the two age groups after intervention. Changes in adipose tissue and skeletal muscle transcriptomes were marginal. Analysis of the differential response to the lifestyle intervention showed tenuous differences between age groups. These data suggest that lifestyle intervention combining calorie restriction and exercise shows similar beneficial effects on cardiometabolic risk and insulin sensitivity in younger and older obese men. However, attention must be paid to potential loss of muscle mass in response to weight loss in older obese men.NEW & NOTEWORTHY Rise in obesity and aging worldwide are major trends of critical importance in public health. This study addresses a current challenge in obesity management. Do older obese adults respond differently to a lifestyle intervention composed of moderate calorie restriction and supervised physical activity than younger ones? The main conclusion of the study is that older and younger obese men similarly benefit from the intervention in terms of cardiometabolic risk.

Baseline Metabolic Variables Do Not Predict Weight Regain in Premenopausal Women

OBJECTIVE

The aim of this study was to investigate whether baseline (pre-weight loss) metabolic variables can predict weight regain.

METHODS

About 117 women with overweight completed a weight loss program to achieve BMI < 25 kg/m2 and were followed for 2 years. Resting metabolic rate, respiratory quotient, insulin sensitivity, and serum leptin concentration were measured pre-weight loss, while on energy balance, and as predictors of weight regain at 1 and 2 years. Rate and amount of weight loss also were examined as predictors, as these outcomes may reflect metabolic phenotype.

RESULTS

Average weight loss was 12 (SD 2.5) kg, and regain was 48% (SD 35%) and 80% (SD 52%) at 1 and 2 years, respectively. In regression modeling, metabolic variables (both pre-weight loss and changes with weight loss) did not predict weight regain. However, initial weight loss and time to achieve BMI < 25 were significant predictors of weight regain at 1 and 2 years, even after adjusting for confounders.

CONCLUSIONS

Baseline (pre-weight loss) resting metabolic rate, respiratory quotient, insulin sensitivity, and leptin did not predict weight regain. However, a larger and faster weight loss was associated with a lower weight regain. Understanding the mechanisms behind interindividual variation in magnitude and rate of weight loss is needed to ensure better weight loss maintenance.

OBEDIS Core Variables Project: European Expert Guidelines on a Minimal Core Set of Variables to Include in Randomized, Controlled Clinical Trials of Obesity Interventions

Heterogeneity of interindividual and intraindividual responses to interventions is often observed in randomized, controlled trials for obesity. To address the global epidemic of obesity and move toward more personalized treatment regimens, the global research community must come together to identify factors that may drive these heterogeneous responses to interventions. This project, called OBEDIS (OBEsity Diverse Interventions Sharing - focusing on dietary and other interventions), provides a set of European guidelines for a minimal set of variables to include in future clinical trials on obesity, regardless of the specific endpoints. Broad adoption of these guidelines will enable researchers to harmonize and merge data from multiple intervention studies, allowing stratification of patients according to precise phenotyping criteria which are measured using standardized methods. In this way, studies across Europe may be pooled for better prediction of individuals' responses to an intervention for obesity - ultimately leading to better patient care and improved obesity outcomes.

Low capacity to oxidize fat and body weight

For a given positive energy balance, a low capacity to oxidize fat could contribute to weight gain (low fat oxidation hypothesis). This hypothesis is based on the arguments that for a given stable diet and food quotient (FQ), the respiratory quotient (RQ) is higher in obesity prone (OP) than in obesity resistant individuals (OR) and that a high RQ predicts higher future weight gain. A review of 42 studies shows that there is no convincing experimental support to these arguments and thus for the low fat oxidation hypothesis. A power analysis also shows that this hypothesis might be impossible to experimentally confirm because very large numbers of subjects would be needed to reject the null hypotheses that the 24-h RQ is not different in OP and OR or that future weight gain is not different in individuals with a low and high 24-h RQ at baseline. A re-examination of the significance of the 24-hour and fasting RQ also shows that the assumption underlying the low fat oxidation hypothesis that a high RQ reflects a low capacity to oxidize fat is not valid: For a stable diet, the 24-h RQ entirely depends on FQ and energy balance, and the fasting RQ mainly depends on the FQ and energy balance and on the size of glycogen stores.

Physiological responses to leptin levels in lipodystrophy: a model for other hypoleptinemias?

Brown et al. report that two weeks of exogenous leptin administration to leptin-naive individuals with lipodystrophy resulted in increased energy expenditure and lipolysis, decreased ectopic liver fat, improved hepatic and peripheral insulin sensitivity, and attenuated dyslipidemia. Leptin withdrawal in individuals with lipodystrophy did not produce reciprocal effects on these phenotypes and resulted in significant improvements only in hepatic insulin sensitivity. This asymmetry in responses to leptin initiation and cessation is consistent with the other aspects of leptin biology that are dependent on the metabolic context in which this adipocyte-derived hormone functions.

Weight Gain and Impaired Glucose Metabolism in Women Are Predicted by Inefficient Subcutaneous Fat Cell Lipolysis

Adipocyte mobilization of fatty acids (lipolysis) is instrumental for energy expenditure. Lipolysis displays both spontaneous (basal) and hormone-stimulated activity. It is unknown if lipolysis is important for future body weight gain and associated disturbed glucose metabolism, and this was presently investigated in subcutaneous adipocytes from two female cohorts before and after ≥10-year follow-up. High basal and low stimulated lipolysis at baseline predicted future weight gain (odds ratios ≥4.6) as well as development of insulin resistance and impaired fasting glucose/type 2 diabetes (odds ratios ≥3.2). At baseline, weight gainers displayed lower adipose expression of several established lipolysis-regulating genes. Thus, inefficient lipolysis (high basal/low stimulated) involving altered gene expression is linked to future weight gain and impaired glucose metabolism and may constitute a treatment target. Finally, low stimulated lipolysis could be accurately estimated in vivo by simple clinical/biochemical measures and may be used to identify risk individuals for intensified preventive measures.

Energy Expenditure in Pregnant Women with Obesity Does Not Support Energy Intake Recommendations

OBJECTIVE

This study aimed to identify factors that may predispose women to excess gestational weight gain (GWG).

METHODS

Seventy-two healthy women with obesity (30 class I, 24 class II, 18 class III) expecting a singleton pregnancy were studied at 13 to 16 weeks gestation. Energy expenditure (EE) was measured during sleep (SleepEE, average EE from 0200-0500 hours) in a whole-room calorimeter, and total daily EE (TDEE) over 7 days using doubly labeled water. Glucose, insulin, thyroid hormones, and catecholamines were measured.

RESULTS

Body composition explained 70% variability in SleepEE, and SleepEE accounted for 67% to 73% of TDEE. Though there was no evidence of consistent low metabolism, there was considerable variability. Low SleepEE was associated with insulin resistance and low triiodothyronine concentrations (both P = 0.01). Physical activity level was 1.47 ± 0.02. For women with SleepEE within 100 kcal/d of their predicted EE, TDEE was significantly less than the estimate (2,530 ± 91 vs. 2,939 kcal/d; P < 0.001) provided from the most recent gestational energy requirement model.

CONCLUSIONS

Pregnant women with obesity are inactive, possibly predisposing them to excess GWG. Current energy requirement models overestimate activity and may promote excess GWG in women with obesity. Furthermore, the observed large interindividual variability in basal metabolism may be important to consider when assessing the risk for excess GWG.

Influence of segmental body composition and adiposity hormones on resting metabolic rate and substrate utilization in overweight and obese adults

PURPOSE

Low resting metabolic rate (RMR) and high carbohydrate reliance at rest are associated with weight gain, but are highly variable in obese individuals. This study determined the relationship of total and segmental body composition and adiposity hormones with RMR and respiratory exchange ratio (RER) in overweight and obese adults.

METHODS

In 49 men (n = 23) and premenopausal women (n = 26) [mean ± SD; age = 35.0 ± 8.9 years; body mass index (BMI) = 33.6 ± 5.2 kg·m^-2; percent body fat (%fat) = 40.0 ± 8.0%], RMR and RER were evaluated using indirect calorimetry. Total and segmental body composition [fat mass (FM), percent fat (%fat), lean mass (LM), visceral adipose tissue (VAT)] were estimated using dual-energy X-ray absorptiometry. Fasted blood and saliva samples were analyzed for insulin, leptin, estradiol, and cortisol.

RESULTS

In men (M) and women (W), RMR significantly correlated (p < 0.05) with FM (M: R = 0.535; W: R = 0.784) and LM (M: R = 0.645; W: R = 0.867). Of the segmental measures, trunk LM (M: R = 0.593; W: R = 0.879; p < 0.05) and leg LM (M: R = 0.664; W: R = 0.821; p < 0.05) had the strongest correlations with RMR. In men, but not women, RER significantly correlated with FM (R = 0.449; p = 0.032), trunk FM (R = 0.501; p = 0.015), and VAT (R = 0.456; p = 0.029). In men, RMR positively correlated with cortisol (R = 0.430, p = 0.040) and estradiol (R = 0.649, p = 0.001) and RER positively correlated with insulin (R = 0.525, p = 0.010). In women, RMR positively correlated with insulin (R = 0.570, p = 0.006), but RER was not significantly correlated with hormones (p > 0.05).

CONCLUSIONS

Segmental evaluation of body composition, specifically in the lower extremities and abdomen, may be an effective and efficient way to evaluate metabolic status. Sex-specific evaluations are also imperative.

In Vitro lipolysis is associated with whole-body lipid oxidation and weight gain in humans

OBJECTIVE

To assess the association of adipocyte size with cellular lipolysis and between cellular lipolysis and whole-body lipid oxidation. This study also assessed the association between adipocyte size and cellular lipolysis with weight and fat mass gain.

METHODS

Subjects had assessment of percent body fat (%fat) and adipose tissue biopsy for in vitro lipolysis (n = 325), and a subset of subjects had measurement of whole-body lipid oxidation (n = 112). A subset of subjects (n = 243) returned for repeated measurements of body weight and composition (mean follow-up 8.2 ± 5.5 years).

RESULTS

In vitro lipolysis (r = 0.47, P < 0.0001) and adipocyte size (r = 0.49, P < 0.0001) were strongly associated with %fat. In vitro lipolysis (P = 0.04) but not adipocyte size (P = 0.44) was associated with whole-body fat oxidation. Adipocyte size was not associated with rate of percent weight gain (P = 0.20) but was negatively associated with rate of percent fat mass gain (P = 0.01). In vitro lipolysis was negatively associated with rate of percent weight gain (P = 0.02) and had a marginal negative association with rate of percent fat mass gain (P = 0.08).

CONCLUSIONS

These results indicate inherent characteristics of adipocytes, including size and lipolytic activity, may be important determinants of whole-body lipid oxidation and subsequent weight gain.

Issues in Continuous 24-h Core Body Temperature Monitoring in Humans Using an Ingestible Capsule Telemetric Sensor

BACKGROUND

There is increasing interest in the use of pill-sized ingestible capsule telemetric sensors for assessing core body temperature (Tc) as a potential indicator of variability in metabolic efficiency and thrifty metabolic traits. The aim of this study was to investigate the feasibility and accuracy of measuring Tc using the CorTemp^® system.

METHODS

Tc was measured over an average of 20 h in 27 human subjects, with measurements of energy expenditure made in the overnight fasted state at rest, during standardized low-intensity physical activity and after a 600 kcal mixed meal. Validation of accuracy of the capsule sensors was made ex vivo against mercury and electronic thermometers across the physiological range (35-40°C) in morning and afternoon of 2 or 3 consecutive days. Comparisons between capsule sensors and thermometers were made using Bland-Altman analysis. Systematic bias, error, and temperature drift over time were assessed.

RESULTS

The circadian Tc profile classically reported in free-living humans was confirmed. Significant increases in Tc (+0.2°C) were found in response to low-power cycling at 40-50 W (~3-4 METs), but no changes in Tc were detectable during low-level isometric leg press exercise (<2 METs) or during the peak postprandial thermogenesis induced by the 600 kcal meal. Issues of particular interest include fast "turbo" gut transit with expulsion time of <15 h after capsule ingestion in one out of every five subjects and sudden erratic readings in teletransmission of Tc. Furthermore, ex vivo validation revealed a substantial mean bias (exceeding ±0.5°C) between the Tc capsule readings and mercury or electronic thermometers in half of the capsules. When examined over 2 or 3 days, the initial bias (small or large) drifted in excess of ±0.5°C in one out of every four capsules.

CONCLUSION

Since Tc is regulated within a very narrow range in the healthy homeotherm's body (within 1°C), physiological investigations of Tc require great accuracy and precision (better than 0.1°C). Although ingestible capsule methodology appears of great interest for non-invasively monitoring the transit gut temperature, new technology requires a reduction in the inherent error of measurement and elimination of temperature drift and warrants more interlaboratory investigation on the above factors.

Metabolic characterization of overweight and obese adults

OBJECTIVES

Traditional evaluations of metabolic health may overlook underlying dysfunction in individuals who show no signs of insulin resistance or dyslipidemia. The purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional cardiometabolic variables. A secondary purpose was to evaluate differences between overweight/obese and male/female cohorts, respectively.

METHODS

Forty-nine overweight and obese adults (Mean ± SD; Age = 35.0 ± 8.9 yrs; Body mass index = 33.6 ± 5.2 kg·m-2; Percent body fat [%fat] = 36.7 ± 7.9%) were characterized. Body composition (fat mass [FM], lean mass [LM], %fat) was calculated using a 4-compartment model; visceral adipose tissue (VAT) was quantified using B-mode ultrasound. Resting metabolic rate (RMR) and respiratory exchange ratio (RER) were evaluated using indirect calorimetry. Fasted blood and saliva samples were analyzed for total cholesterol (TC), high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglycerides (TRG), glucose (GLUC), insulin, leptin, estradiol, and cortisol.

RESULTS

The prevalence of individuals with two or more cardiometabolic risk factors increased from 13%, using traditional risk factors (GLUC, TRG, HDL), to 80% when non-traditional metabolic factors (VAT, LM, RMR, RER, TC, LDL, HOMA-IR) were considered. Between overweight/obese, there were no significant differences in %fat (p = 0.152), VAT (p = 0.959), RER (p = 0.493), lipids/GLUC (p > 0.05), insulin (p = 0.143), leptin (p = 0.053), or cortisol (p = 0.063); obese had higher FM, LM, RMR, and estradiol (p < 0.01). Males had greater LM, RMR, and TRG (p < 0.01); females had greater %fat, and leptin (p < 0.001). There were no significant sex differences in RER, estradiol, insulin, or cortisol (p > 0.05).

CONCLUSIONS

Evaluating metabolic health beyond BMI and traditional cardiometabolic risk factors can give significant insights into metabolic status. Due to high variability in metabolic health in overweight and obese adults and inherent sex differences, implementation of body composition and visceral fat measures in the clinical setting can improve early identification and approaches to disease prevention.

Voluntary Running Aids to Maintain High Body Temperature in Rats Bred for High Aerobic Capacity

The production of heat, i.e., thermogenesis, is a significant component of the metabolic rate, which in turn affects weight gain and health. Thermogenesis is linked to physical activity (PA) level. However, it is not known whether intrinsic exercise capacity, aging, and long-term voluntary running affect core body temperature. Here we use rat models selectively bred to differ in maximal treadmill endurance running capacity (Low capacity runners, LCR and High capacity Runners, HCR), that as adults are divergent for aerobic exercise capacity, aging, and metabolic disease risk to study the connection between PA and body temperature. Ten high capacity runner (HCR) and ten low capacity runner (LCR) female rats were studied between 9 and 21 months of age. Rectal body temperature of HCR and LCR rats was measured before and after 1-year voluntary running/control intervention to explore the effects of aging and PA. Also, we determined whether injected glucose and spontaneous activity affect the body temperature differently between LCR and HCR rats at 9 vs. 21 months of age. HCRs had on average 1.3°C higher body temperature than LCRs (p < 0.001). Aging decreased the body temperature level of HCRs to similar levels with LCRs. The opportunity to run voluntarily had a significant impact on the body temperature of HCRs (p < 0.001) allowing them to maintain body temperature at a similar level as when at younger age. Compared to LCRs, HCRs were spontaneously more active, had higher relative gastrocnemius muscle mass and higher UCP2, PGC-1α, cyt c, and OXPHOS levels in the skeletal muscle (p < 0.050). These results suggest that higher PA level together with greater relative muscle mass and higher mitochondrial content/function contribute to the accumulation of heat in the HCRs. Interestingly, neither aging nor voluntary training had a significant impact on core body temperature of LCRs. However, glucose injection resulted in a lowering of the body temperature of LCRs (p < 0.050), but not that of HCRs. In conclusion, rats born with high intrinsic capacity for aerobic exercise and better health have higher body temperature compared to rats born with low exercise capacity and disease risk. Voluntary running allowed HCRs to maintain high body temperature during aging, which suggests that high PA level was crucial in maintaining the high body temperature of HCRs.

A Human Thrifty Phenotype Associated With Less Weight Loss During Caloric Restriction

Successful weight loss is variable for reasons not fully elucidated. Whether effective weight loss results from smaller reductions in energy expenditure during caloric restriction is not known. We analyzed whether obese individuals with a "thrifty" phenotype, that is, greater reductions in 24-h energy expenditure during fasting and smaller increases with overfeeding, lose less weight during caloric restriction than those with a "spendthrift" phenotype. During a weight-maintaining period, 24-h energy expenditure responses to fasting and 200% overfeeding were measured in a whole-room indirect calorimeter. Volunteers then underwent 6 weeks of 50% caloric restriction. We calculated the daily energy deficit (kilocalories per day) during caloric restriction, incorporating energy intake and waste, energy expenditure, and daily activity. We found that a smaller reduction in 24-h energy expenditure during fasting and a larger response to overfeeding predicted more weight loss over 6 weeks, even after accounting for age, sex, race, and baseline weight, as well as a greater rate of energy deficit accumulation. The success of dietary weight loss efforts is influenced by the energy expenditure response to caloric restriction. Greater decreases in energy expenditure during caloric restriction predict less weight loss, indicating the presence of thrifty and spendthrift phenotypes in obese humans.

Drug development strategies for the treatment of obesity: how to ensure efficacy, safety, and sustainable weight loss

The prevalence of obesity has increased worldwide, and approximately 25%-35% of the adult population is obese in some countries. The excess of body fat is associated with adverse health consequences. Considering the limited efficacy of diet and exercise in the current obese population and the use of bariatric surgery only for morbid obesity, it appears that drug therapy is the only available method to address the problem on a large scale. Currently, pharmacological obesity treatment options are limited. However, new antiobesity drugs acting through central nervous system pathways or the peripheral adiposity signals and gastrointestinal tract are under clinical development. One of the most promising approaches is the use of peptides that influence the peripheral satiety signals and brain-gut axis such as GLP-1 analogs. However, considering that any antiobesity drug may affect one or several of the systems that control food intake and energy expenditure, it is unlikely that a single pharmacological agent will be effective as a striking obesity treatment. Thus, future strategies to treat obesity will need to be directed at sustainable weight loss to ensure maximal safety. This strategy will probably require the coadministration of medications that act through different mechanisms.

Metabolic determinants of body weight after cats were fed a low-carbohydrate high-protein diet or a high-carbohydrate low-protein diet ad libitum for 8 wk

Overweight and obese conditions are common in cats and are associated with the development of a number of diseases. Knowledge of metabolic determinants and predictors of weight gain may enable better preventative strategies for obesity in cats. Lean, healthy cats were fed either a low-carbohydrate high-protein diet (n 16) or a high-carbohydrate low-protein (n 16) diet ad libitum for 8 wk. Potential determinants and predictors of final body weight assessed were body fat and lean masses, energy required for maintenance, energy requirements above maintenance for each kilogram of weight gain, insulin sensitivity index, fasting, mean 24-h and peak plasma glucose, insulin, and leptin concentrations, and fasting and mean 24-h serum adiponectin concentrations. In cats fed the low-carbohydrate high-protein diet, after adjusting for initial body weight, those with higher energy requirements for weight gain and higher fasting glucose concentration had higher final body weights (P ≤ 0.01). Predicted final body weights using initial body weight, fasting glucose and mean 24-h insulin concentrations (partial R(2) 37.3%) were imprecise. An equation using just initial body weight and fasting glucose concentration would be of more practical value, but was marginally less precise. In cats fed the high-carbohydrate low-protein diet, those with lower fasting leptin concentration initially had higher final body weights (P = 0.01). Predicted final body weights using initial body weight, energy requirements for maintenance, total body fat percentage and fasting leptin concentration (partial R(2) 39.2%) were reasonably precise. Further studies are warranted to confirm these findings and to improve the precision of predicted final body weights.

Adipokines - removing road blocks to obesity and diabetes therapy

Prevention of obesity and therapeutic weight loss interventions have provided only limited long term success. Therefore there is an urgent need to develop novel pharmacological treatment strategies, which target mechanisms underlying positive energy balance, excessive fat accumulation and adverse fat distribution. Adipokines may have potential for future pharmacological treatment strategies of obesity and metabolic diseases, because they are involved in the regulation of appetite and satiety, energy expenditure, endothelial function, blood pressure, insulin sensitivity, adipogenesis, fat distribution and insulin secretion and others. There are important road blocks on the way from an adipokine candidate to the clinical use a therapeutic compound. Such road blocks include an incomplete understanding of the mechanism of action, resistance to a specific adipokine, side effects of the adipokine and others. This review focuses on the potential of selected adipokines as therapeutic tools or targets and discusses important road blocks, which currently prevent their clinical use.

The influence of oral water load on energy expenditure and sympatho-vagal balance in obese and normal weight women

INTRODUCTION

Oral water load may increase the energy expenditure (EE) by stimulation of sympathetic dependent thermogenesis. Thus, drinking of water may be helpful in weight reduction. The aim of the study is to assess the influence of water load on energy expenditure and sympathetic activity in obese and normal weight women.

MATERIAL AND METHODS

Forty-five women were included. Energy expenditure was measured twice, in the morning and after oral water load, by the indirect calorimetric method. The heart rate variability parameters low frequency (LF), high frequency (HF), LF/HF index, standard deviation of normal RR intervals (SDNN) and root mean square difference among successive RR normal intervals (rMSSD) were used for the indirect assessment of the sympatho-vagal balance.

RESULTS

Resting energy expenditure (REE) was significantly higher in obese than in normal weight women (1529 ±396 kcal/day vs. 1198 ±373 kcal/day; p = 0.02). In both study groups after water load EE increased significantly (by 20% and by 12%, corresponding to 8.6 kcal/h and 5.2 kcal/h respectively), while, LF/HF index increased simultaneously. The increase of energy expenditure (EE) did not exceed the energetic cost of water heating, from room to body temperature - 15 kcal/1000 ml. There was no correlation between changes of energy expenditure (EE) and heart rate variability (HRV) parameters.

CONCLUSIONS

The increase of EE induced by water load is mostly related to the heating of the consumed water to body temperature. The assessment of autonomic balance by means of standard HRV indices had been found insufficient for detection of actually operating mechanisms.

Efficiency of Walking and Stepping: Relationship to Body Fatness

OBJECTIVE

To determine energetic efficiency of walking and stepping in a heterogeneous normal adult population and its association with body fatness and to assess within- and between-individual variations.

RESEARCH METHODS AND PROCEDURES

Using a combination of a whole-room indirect calorimeter and a large precision force platform, we simultaneously measured minute-by-minute energy expenditure (EE) and mechanical work during walking and stepping in healthy adult men (n = 60) and women (n = 85). Efficiency was calculated as a ratio (percentage) of mechanical work and EE of activity. Efficiency of walking and stepping performed at various intensities was compared for reproducibility within the same day (morning and afternoon) and correlated with a subject's characteristics.

RESULTS

The efficiency of walking was negatively correlated with body fatness in both men and women at 0.9 to 1.2 m/s but positively correlated with body fatness in men and not correlated in women at the slowest speed tested (0.6 m/s). Efficiency of walking and stepping of various intensities was reproducible during the same day. Compared at similar EE levels, walking was more efficient than stepping (26% to 27% vs. 18% to 22%, p < 0.01). Women were significantly (p < 0.01) more efficient than men during stepping. Age, sex, body mass, fat-free mass, fitness (maximal oxygen uptake), height, and speed variations contributed to the between-subject differences in efficiency.

DISCUSSION

Obese individuals were less efficient than lean individuals during normal-speed walking. Significant interindividual variations in efficiency of walking and stepping may be attributed to habituation and physical characteristics such as age, sex, and fitness level.

Factors predicting nongenetic variability in body weight gain induced by a high-fat diet in inbred C57BL/6J mice

Inbred C57BL/6J mice displayed large individual variations in weight gain when fed a high-fat diet (HFD). The objective of this study was to examine whether this predominantly nongenetic variability could be predicted by relevant baseline features and to explore whether variations in these significant features were influenced during pregnancy and/or lactation. Fat mass (FM), fat-free mass (FFM), food intake (FI), resting metabolic rate (RMR), physical activity (PA), and body temperature (T(b)) were all evaluated at baseline in 60 mice (aged 10-12 weeks) before HFD feeding. Regression analyses showed that baseline FM was a strong positive predictor of weight gain between 4 and 16 weeks of HFD. Baseline PA was negatively associated with weight gain at week 8, 12, and 16, and baseline FFM had a positive effect at week 12 and 16. In a second experiment, 40 female mice were mated and litter sizes (LS) were manipulated on day 3 of lactation. Weaning weight and postweaning growth rate (GR) had positive impacts on FM and FFM at age 9 weeks (FM, P = 0.001; FFM, P < 0.001: n = 97). Lactation LS had a negative effect on weaning weight and a positive effect on postweaning GR. In conclusion, our results show that obesity induced by HFD was associated with a higher baseline FM, a higher baseline FFM and a lower baseline PA level before the exposure of HFD. Two of these traits (FM and FFM) were influenced by lactation LS via weaning weight and postweaning GR.

Selective estrogen receptor modulator promotes weight loss in ovariectomized female rhesus monkeys (Macaca mulatta) by decreasing food intake and increasing activity

The effect of hormone replacement therapy (HRT) on body weight in postmenopausal women is controversial, with studies reporting an increase, a decrease, and no change in body weight. To examine estrogen receptor actions on body weight, we investigated the effects of treatment with a selective estrogen receptor modulator (SERM) on body weight, food intake, and activity and metabolic rate in a nonhuman primate model. Eighteen ovariectomized female rhesus monkeys were treated with a nonsteroidal SERM (GSK232802A, 5 mg/kg po) for 3 mo. GSK232802A decreased lutenizing hormone (P < 0.0001) and follicle-stimulating hormone levels (P < 0.0001), consistent with the estrogenic action of the compound. GSK232802A treatment produced a small but sustained weight loss (4.6 ± 1.0%, P < 0.0001) and reduced adiposity (P < 0.0001), which was due at least in part to a suppression of food intake (3.6 ± 3.7%, P < 0.0001). Physical activity increased during the 3rd mo of treatment (P = 0.04). Baseline activity level and the change in activity due to treatment were correlated, with the most sedentary individuals exhibiting increased physical activity during the 1st mo of treatment (P = 0.02). Metabolic rate did not change (P = 0.58). These results indicate that GSK232802A treatment reduces body weight and adiposity in ovariectomized nonhuman primates by suppressing food intake and increasing activity, particularly in the most sedentary individuals. These findings suggest that SERM treatment may counteract weight gain in postmenopausal women.

The search for compounds that stimulate thermogenesis in obesity management: from pharmaceuticals to functional food ingredients

The concept of managing obesity through the stimulation of thermogenesis is currently a focus of considerable attention by the pharmaceutical, nutraceutical and functional food industries. This paper first reviews the landmark discoveries that have fuelled the search for thermogenic anti-obesity products that range from single-target drugs to multi-target functional foods. It subsequently analyses the thermogenic and fat-oxidizing potentials of a wide array of bioactive food ingredients which are categorized under methylxanthines, polyphenols, capsaicinoids/capsinoids, minerals, proteins/amino acids, carbohydrates/sugars and fats/fatty acids. The main outcome of this analysis is that the compounds or combination of compounds with thermogenic and fat-oxidizing potentials are those that possess both sympathomimetic stimulatory activity and acetyl-coA carboxylase inhibitory property, and are capable of targeting both skeletal muscle and brown adipose tissue. The thermogenic potentials of products so far tested in humans range from marginal to modest, i.e. 2-5% above daily energy expenditure. With an increasing number of bioactive food ingredients awaiting screening in humans, there is hope that this thermogenic potential could be safely increased to 10-15% above daily energy expenditure - which would have clinically significant impact on weight management, particularly in the prevention of obesity and in improving the long-term prognosis of post-slimming weight maintenance.

Body weight, not insulin sensitivity or secretion, may predict spontaneous weight changes in nondiabetic and prediabetic subjects: the RISC study

OBJECTIVE

Previous studies have found that high insulin sensitivity predicts weight gain; this association has not been confirmed. Our aim was to systematically analyze metabolic predictors of spontaneous weight changes.

RESEARCH DESIGN AND METHODS

In 561 women and 467 men from the Relationship Between Insulin Sensitivity and Cardiovascular Disease (RISC) cohort (mean age 44 years, BMI range 19-44 kg/m(2), 9% impaired glucose tolerance) followed up for 3 years, we measured insulin sensitivity (by a euglycemic clamp) and β-cell function (by modeling of the C-peptide response to oral glucose and by acute insulin response to intravenous glucose).

RESULTS

Insulin sensitivity was similar in weight gainers (top 20% of the distribution of BMI changes), weight losers (bottom 20%), and weight stable subjects across quartiles of baseline BMI. By multiple logistic or linear regression analyses controlling for center, age, sex, and baseline BMI, neither insulin sensitivity nor any β-cell function parameter showed an independent association with weight gain; this was true in normal glucose tolerance, impaired glucose tolerance, and whether subjects progressed to dysglycemia or not. Baseline BMI was significantly higher in gainers (26.1 ± 4.1 kg/m(2)) and losers (26.6 ± 3.7 kg/m(2)) than in weight stable subjects (24.8 ± 3.8 kg/m(2), P<0.0001 for both gainers and losers). Baseline waist circumference (or equivalently, BMI or weight) was a positive, independent predictor of both weight gain and weight loss (odds ratio 1.48 [95% CI 1.12-1.97]) in men and (1.67 [1.28-2.12]) in women. In men only, better insulin sensitivity was an additional independent predictor of weight loss.

CONCLUSIONS

Neither insulin sensitivity nor insulin secretion predicts spontaneous weight gain. Individuals who have attained a higher weight are prone to either gaining or losing weight regardless of their glucose tolerance.

Poor prediction of resting energy expenditure in obese women by established equations

The objective of the study was to evaluate the accuracy of established prediction equations that calculate resting energy expenditure (REE) in obese women. This was a cross-sectional study. In 273 mildly to severely obese women (age, 41.7 +/- 13.2 years; body mass index, 42.8 +/- 7.0 kg/m(2)), REE was measured by indirect calorimetry (mREE), along with fat mass (FM) and fat-free mass (FFM) by bioelectrical impedance analysis. Eleven established equations were used to predict REE (pREE), with 9 equations basing on the anthropometric parameters body weight and height and 2 equations including body composition parameters (FM, FFM). All equations provided pREE values that significantly correlated with mREE (r > 0.66, P < .001), although 8 equations systematically underestimated mREE (P < .05). Of note, even the best equation was not able to accurately predict mREE with a deviation of less than +/-10% in more than 70% of the tested women. Furthermore, equations using body composition data were not superior in predicting REE as compared with equations exclusively including anthropometric variables. Multiple linear regression analyses revealed 2 new equations--one including body weight and age and another including FM, FFM, and age--that explained 56.9% and 57.2%, respectively, of variance in mREE. However, when these 2 new equations were applied to an independent sample of 33 obese women, they also provided an accurate prediction (+/-10%) of mREE in only 56.7% and 60.6%, respectively, of the women. Data show that an accurate prediction of REE is not feasible using established equations in obese women. Equations that include body composition parameters as assessed by bioelectrical impedance analysis do not increase the accuracy of prediction. Based on our results, we conclude that calculating REE by standard prediction equations does not represent a reliable alternative to indirect calorimetry for the assessment of REE in obese women.

Obesity is a sign - over-eating is a symptom: an aetiological framework for the assessment and management of obesity

Obesity is characterized by the accumulation of excess body fat and can be conceptualized as the physical manifestation of chronic energy excess. Using the analogy of oedema, the consequence of positive fluid balance or fluid retention, obesity can be seen as the consequence of positive energy balance or calorie 'retention'. Just as the assessment of oedema requires a comprehensive assessment of factors related to fluid balance, the assessment of obesity requires a systematic assessment of factors potentially affecting energy intake, metabolism and expenditure. Rather than just identifying and describing a behaviour ('this patient eats too much'), clinicians should seek to identify the determinants of this behaviour ('why, does this patient eat too much?'). This paper provides an aetiological framework for the systematic assessment of the socio-cultural, biomedical, psychological and iatrogenic factors that influence energy input, metabolism and expenditure. The paper discusses factors that affect metabolism (age, sex, genetics, neuroendocrine factors, sarcopenia, metabolically active fat, medications, prior weight loss), energy intake (socio-cultural factors, mindless eating, physical hunger, emotional eating, mental health, medications) and activity (socio-cultural factors, physical and emotional barriers, medications). It is expected that the clinical application of this framework can help clinicians systematically assess, identify and thereby address the aetiological determinants of positive energy balance resulting in more effective obesity prevention and management.

Prospective association between fasting NEFA and type 2 diabetes: impact of post-load glucose

AIMS/HYPOTHESIS

Elevated fasting NEFAs are thought to promote type 2 diabetes. Three prospective studies support this concept, showing increased diabetes risk associated with fasting NEFA. However, these prospective associations may be confounded by strong cross-sectional correlations between fasting NEFA and metabolic predictors of diabetes. To examine this assumption, we used cohort data from the Insulin Resistance Atherosclerosis Study (IRAS).

METHODS

Within the IRAS cohort (n = 902, 145 incident cases), we examined nine metabolic variables for their confounding effect on the fasting NEFA-diabetes association: 2 h glucose; fasting plasma glucose; body mass index; waist circumference; waist-to-hip ratio; weight; insulin sensitivity (S (I)); fasting insulin; and acute insulin response. We compared odds ratios for fasting NEFA (log( e ) transformed and adjusted for age, sex, ethnicity and clinic) before and after inclusion of each metabolic variable into a logistic regression model.

RESULTS

Three variables (2 h glucose, BMI and S (I)) cross-sectionally correlated with fasting NEFA (r > or = 0.1, p < 0.05). Unadjusted for metabolic predictors, fasting NEFA levels were positively associated with diabetes risk: OR 1.37 (95% CI 0.87-2.15) per unit on a log scale. All metabolic variables except AIR showed confounding. Inclusion of 2 h glucose reversed the positive association (OR 0.50 [95% CI 0.30-0.82]), whereas other predictors reduced the association to the null. The final model included the variables correlated with baseline fasting NEFA (2 h glucose, BMI and S (I)) and the demographic variables resulting in OR 0.47 (95% CI 0.27-0.81).

CONCLUSIONS/INTERPRETATION

Our results indicate that 2 h glucose strongly confounds the prospective association between fasting NEFA and diabetes; carefully adjusted fasting NEFA levels are inversely associated with diabetes risk.

Biochemical risk factors for development of obesity in first-episode schizophrenia

Obesity is a serious health issue for many patients with schizophrenia. There is a lack of predictors for and understanding of the development of obesity in the early phase of the illness. Therefore we investigated a set of routine biochemistry variables in blood as predictors of the development of obesity and weight gain over 5 years in an observational cohort study of patients with first-episode schizophrenia (n=59). Twelve percent of the patients were obese at baseline and 37% were obese at the 5-year follow-up. The mean body mass index (BMI) change over 5 years was a 4.1 kg/m(2) increase (4.5 SD). Obesity was predicted by baseline hemoglobin levels (odds ratio per standard deviation [OR/SD] 3.3, 95% confidence interval [CI] 1.4 to 7.5), red blood cell count (OR/SD 2.6, 95% CI 1.2 to 5.5), hematocrit (OR/SD 2.8, 95% CI 1.3 to 5.9), gamma-glutamyltransferase (OR/SD 2.8, 95% CI 1.2-6.3) and creatinine (OR/SD 3.1, 95% CI 1.2 to 8.0). After adjustment for baseline BMI, the associations were attenuated for gamma-glutamyltransferase and creatinine. Low baseline BMI was associated with a greater BMI increase. The major conclusion is that easily available routine biochemistry markers can be useful in predicting the development of obesity in first-episode schizophrenia. The mechanisms underlying the observed associations are unknown, but the predictors identified in this study could signify dehydration or insulin resistance. These observations open a new window to future research on the mechanisms underlying the development of obesity in schizophrenia.

Do mechanical gait parameters explain the higher metabolic cost of walking in obese adolescents?

Net metabolic cost of walking normalized by body mass ( CW·BM−1; in J·kg−1·m−1) is greater in obese than in normal-weight individuals, and biomechanical differences could be responsible for this greater net metabolic cost. We hypothesized that, in obese individuals, greater mediolateral body center of mass (COM) displacement and lower recovery of mechanical energy could induce an increase in the external mechanical work required to lift and accelerate the COM and thus in net CW·BM−1. Body composition and standing metabolic rate were measured in 23 obese and 10 normal-weight adolescents. Metabolic and mechanical energy costs were assessed while walking along an outdoor track at four speeds (0.75–1.50 m/s). Three-dimensional COM accelerations were measured by means of a tri-axial accelerometer and gyroscope and integrated twice to obtain COM velocities, displacements, and fluctuations in potential and kinetic energies. Last, external mechanical work (J·kg−1·m−1), mediolateral COM displacement, and the mechanical energy recovery of the inverted pendulum were calculated. Net CW·BM−1 was 25% higher in obese than in normal-weight subjects on average across speeds, and net CW·BM−67 (J·kg−0.67·m−1) was significantly related to percent body fat ( r2 = 0.46). However, recovery of mechanical energy and the external work performed (J·kg−1·m−1) were similar in the two groups. The mediolateral displacement was greater in obese subjects and significantly related to percent body fat ( r2 = 0.64). The mediolateral COM displacement, likely due to greater step width, was significantly related to net CW·BM−67 ( r2 = 0.49). In conclusion, we speculate that the greater net CW·BM−67 in obese subjects may be partially explained by the greater step-to-step transition costs associated with wide gait during walking.

Beta3-adrenoceptor function and long-term changes in body weight

BACKGROUND

The endogenous factors contributing to long-term changes in body weight are not known but the regulation of energy metabolism by different beta-adrenoceptors (beta(1)-AR, beta(2)-AR, beta(3)-AR) or alpha-adrenoceptors (alpha(2)-AR) may play a role.

METHODS

In a prospective study, we investigated beta-AR and alpha(2)-AR subtype function in subcutaneous fat cells of 85 healthy, non-obese women by using a standardized bioassay of lipolysis. Of these 73 were re-investigated on an average 10 years later to compare baseline function of beta(1)-AR, beta(2)-AR, beta(3)-AR and alpha(2)-AR with longitudinal weight changes.

RESULTS

Weight change over time was normally distributed ranging from-4 kg/m(2) to +6 kg/m(2) in body mass index. Long-term changes in body weight correlated inversely with beta(3)-AR function at base line (r=0.5, P=0.001). Those with low beta(3)-AR function gained weight, whereas the opposite was observed with those who had a high beta(3)-AR function. Nineteen percent of weight changes could be explained by beta(3)-AR status. No relationship with weight changes was observed as regards the function of alpha(2)-AR, beta(1)-AR or beta(2)-AR function.

CONCLUSIONS

Beta(3)-ARs are important for long-term changes in body weight putting energy metabolism in adipose tissue in frontline among endogenous factors that regulate body weight in adulthood.

L-carnitine supplementation and physical exercise restore age-associated decline in some mitochondrial functions in the rat

In mammals, during the aging process, an atrophy of the muscle fibers, an increase in body fat mass, and a decrease in skeletal muscle oxidative capacities occur. Compounds and activities that interact with lipid oxidative metabolism may be useful in limiting damages that occur in aging muscle. In this study, we evaluated the effect of L-carnitine and physical exercise on several parameters related to muscle physiology. We described that supplementing old rats with L-carnitine at 30 mg/kg body weight for 12 weeks (a) allowed the restoration of L-carnitine level in muscle cells, (b) restored muscle oxidative activity in the soleus, and (c) induced positive changes in body composition: a decrease in abdominal fat mass and an increase in muscle capabilities without any change in food intake. Moderate physical exercise was also effective in (a) limiting fat mass gain and (b) inducing an increase in the capacities of the soleus to oxidize fatty acids.

Gene-nutrient and gene-physical activity summary--genetics viewpoint

The workshop reviewed the literature indicating that natural alleles influence a substantial percentage of responses to nutrition and exercise in both humans and animal models. Human genetic studies provide evidence that body weight response to over- and underfeeding and to exercise is associated with specific genes. Studies in animal models, primarily rodents, prove the genetic control of responsiveness to diet and exercise and provide the tools to examine specific mechanisms. Limitations of the animal literature include lack of studies of allelic contributions to weight loss in response to diet restriction and data on evidence-based diets.Discussion of the relative merits of sample size constraints vs. precision of phenotype measures in human genetic studies concluded that imprecise measures such as body weight and body mass index identify different genes than will specific measures of fat mass. Validation and limitations of whole genome association studies in humans was discussed, as was the role of animal models in discovery and mechanistic studies of gene/nutrition/exercise interactions.The workshop concluded that genetics has a substantial impact on responses to both diet and exercise. However, current knowledge does not allow individual diet and exercise recommendations. New resources and technologies, including cost-effective phenotyping for humans and whole genome sequencing in both humans and rodents, are needed.

Thrifty genes for obesity, an attractive but flawed idea, and an alternative perspective: the 'drifty gene' hypothesis

Almost 50 years ago Neel proposed a hypothesis to explain the prevalence of obesity and diabetes in modern society--the 'thrifty gene' hypothesis. The fundamental basis of the hypothesis was that, in our early evolutionary history, genes, that promoted efficient fat deposition would have been advantageous because they allowed their holders to survive at periods of famine. In modern society, such genes are disadvantageous because they promote fat deposition in preparation for a famine that never comes, and the result is widespread obesity and diabetes. In recent years I, and others, have questioned some of the fundamental assumptions of this hypothesis--particularly focusing on whether differential survival of lean against obese in famines provides sufficient selective pressure for the spread of so-called 'thrifty genes'. These arguments have been criticized because famines not only affect survival but also fecundity, and obese people would be expected to sustain fecundity longer in the face of food shortages. In this paper, I show that the reduced fecundity argument is flawed because famines are almost universally followed by periods of enhanced fecundity, which offsets the decline observed during the famine itself. The net effect of famines on fecundity is consequently insufficient to rescue the thrifty gene idea. Elsewhere, I have suggested an alternative scenario that subsections of the population have a genetic predisposition to obesity due to an absence of selection, combined with genetic drift. The scenario presented earlier was based on evidence from prehistory concerning the release of our ancestors from heavy predation pressure around 2 million years ago. I suggest here that this is one of a number of potential scenarios based on random genetic drift that may explain the specific aetiology of the obesity epidemic. Together, these alternatives, based on central notion that genetic drift rather than positive selection was a dominant factor, may be called the 'drifty gene' hypothesis.

Relevance of animal models to human eating disorders and obesity

BACKGROUND AND RATIONALE

This review addresses the role animal models play in contributing to our knowledge about the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN) and obesity.

OBJECTIVES

Explore the usefulness of animal models in complex biobehavioral familial conditions, such as AN, BN, and obesity, that involve interactions among genetic, physiologic, psychological, and cultural factors.

RESULTS AND CONCLUSIONS

The most promising animal model to mimic AN is the activity-based anorexia rodent model leading to pathological weight loss. The paradigm incorporates reward elements of the drive for activity in the presence of an appetite and allows the use of genetically modified animals. For BN, the sham-feeding preparation in rodents equipped with a gastric fistula appears to be best suited to reproduce the postprandial emesis and the defects in satiety. Animal models that incorporate genes linked to behavior and mood may clarify biobehavioral processes underlying AN and BN. By contrast, a relative abundance of animal models has contributed to our understanding of human obesity. Both environmental and genetic determinants of obesity have been modeled in rodents. Here, we consider single gene mutant obesity models, along with models of obesigenic environmental conditions. The contributions of animal models to obesity research are illustrated by their utility for identifying genes linked to human obesity, for elucidating the pathways that regulate body weight and for the identification of potential therapeutic targets. The utility of these models may be further improved by exploring the impact of experimental manipulations on the behavioral determinants of energy balance.

Reduced capacity for fatty acid oxidation in rats with inherited susceptibility to diet-induced obesity

High-fat, energy-dense diets promote weight gain and obesity in humans and other animals, but the mechanisms underlying such diet-induced obesity remain elusive. To determine whether a reduced capacity to oxidize fat is involved in the etiology of diet-induced obesity, we examined different measures of fatty acid oxidation in rats selectively bred for susceptibility (DIO) or resistance (DR) to dietary obesity before and after they were fed a high-fat diet and became obese. DIO rats eating a low-fat diet oxidized less dietary fatty acid in vivo and had lower levels of plasma ketone bodies during fasting compared with DR rats. Lean DIO rats fed a low-fat diet showed reduced liver messenger RNA expression of CD36, which transports fatty acids across cell membranes, and long-chain acyl-coenzyme A dehydrogenase (ACADL), which catalyzes the first step in the mitochondrial beta-oxidation of fatty acids. The deficit in CD36 and ACADL messenger RNA expression was also seen in obese DIO rats that had been eating a high-fat diet and, in addition, was accompanied by reduced expression of liver carnitine palmitoyl transferase I, the enzyme that mediates transport of long-chain fatty acids into mitochondria. No differences were found in the expression of liver enzymes involved in fat synthesis; however, in muscle, DIO rats fed the low-fat, but not high-fat, diet showed greater expression of diacylglycerol O-acyltransferase 1 and lipoprotein lipase than did DR rats. Expression of muscle enzymes involved in fatty acid oxidation was similar in the 2 groups. These findings provide a metabolic mechanism for the development of diet-induced obesity and thus suggest potential targets for intervention strategies to treat or prevent it.

Metabolic and behavioral predictors of weight gain in Hispanic children: the Viva la Familia Study

BACKGROUND

Despite the high prevalence of overweight among Hispanic children in the United States, definitive predictors of weight gain have not been identified in this population.

OBJECTIVE

The study objective was to test sociodemographic, metabolic, and behavioral predictors of 1-y weight gains in a large cohort of Hispanic children studied longitudinally.

DESIGN

Subjects (n = 879) were siblings from 319 Hispanic families enrolled in the Viva la Familia Study. Families were required to have at least one overweight child aged 4-19 y. One-year changes in weight and body composition by dual-energy X-ray absorptiometry were measured. Data were from parental interviews, birth certificates, multiple-pass 24-h dietary recalls, 3-d accelerometry, 24-h respiration calorimetry, measurements of eating in the absence of hunger, and measurement of fasting blood biochemistry indexes by radioimmunoassay. Generalized estimating equations and principal component analysis were applied.

RESULTS

Weight gain increased with age (P = 0.001), peaking at approximately 10 y of age in girls and approximately 11 y of age in boys. Mean (+/-SD) weight gain was significantly higher in overweight (7.5 +/- 3.7 kg/y) than in nonoverweight (4.4 +/- 2.4 kg/y) children and in boys than in girls. When adjusted for age, age squared, sex, and Tanner stage, the final model indicated a child's body mass index (BMI; kg/m2) status, maternal BMI, energy expenditure (total energy expenditure, basal metabolic rate, and sleeping metabolic rate), and fasting blood biochemistry indexes (total triiodothyronine, insulin, leptin, and ghrelin) as independent, positive predictors of weight gain (P = 0.01-0.001).

CONCLUSION

Knowledge of the metabolic and behavioral predictors of weight gain in Hispanic children will inform prevention and treatment efforts to address this serious public health problem in the United States.

BMR variability in women of different weight

BACKGROUND & AIMS

Non-exercise activity thermogenesis (NEAT) and substrate oxidation are significant components of Energy Balance; their regulation may be modulated according to nutritional status and their impairment has been advocated as a factor facilitating the development of excess body fat.

METHODS

In this study body composition, resting metabolic rate (RMR), fidgeting as a component of NEAT and respiratory quotient (RQ), an index of preferential substrate oxidation, have been evaluated in 80 young women: 20 restrictive anorexia nervosa (rAN: BMI 15.1+/-1.6 kg/m(2)); 20 constitutional leanness (CL: BMI 17.2+/-1.0); 20 obese patients (Ob: BMI 43.8+/-10.0) and 20 controls (CTR: BMI 21.7+/-2.4).

RESULTS

Fat free mass, fat mass and RMR progressively increased from rAN to Ob (p < 0.05). Fidgeting was higher in CL (67.2+/-27.2 kcal; p < 0.05) than in the other groups. Lipid oxidation, evaluated with RQ showed a negative correlation with fidgeting in CL (r=-0.433; p<0.05) and positive in Ob (r=0.572; p<0.05) and in rAN (r=0.434; p<0.05).

CONCLUSION

Our findings support the regulatory function of NEAT, its protective role to prevent excess body fat accumulation and its positive relation with fat oxidation in CL.

Differences in postprandial responses to fat and carbohydrate loads in habitual high and low fat consumers (phenotypes)

The present study investigated metabolic responses to fat and carbohydrate ingestion in lean male individuals consuming an habitual diet high or low in fat. Twelve high-fat phenotypes (HF) and twelve low-fat phenotypes (LF) participated in the study. Energy intake and macronutrient intake variables were assessed using a food frequency questionnaire. Resting (RMR) and postprandial metabolic rate and substrate oxidation (respiratory quotient; RQ) were measured by indirect calorimetry. HF had a significantly higher RMR and higher resting heart rate than LF. These variables remained higher in HF following the macronutrient challenge. In all subjects the carbohydrate load increased metabolic rate and heart rate significantly more than the fat load. Fat oxidation (indicated by a low RQ) was significantly higher in HF than in LF following the fat load; the ability to oxidise a high carbohydrate load did not differ between the groups. Lean male subjects consuming a diet high in fat were associated with increased energy expenditure at rest and a relatively higher fat oxidation in response to a high fat load; these observations may be partly responsible for maintaining energy balance on a high-fat (high-energy) diet. In contrast, a low consumer of fat is associated with relatively lower energy expenditure at rest and lower fat oxidation, which has implications for weight gain if high-fat foods or meals are periodically introduced to the diet.

Cost-effective measures to prevent obesity: epidemiological basis and appropriate target groups

Cost-effective prevention strategies to prevent weight gain and the development of obesity should be based on appropriate knowledge of the determinants of weight gain. The body of evidence on the dietary determinants of weight gain is, however, fragmentary at best, partly because inappropriate research methods are used to study the determinants of obesity under normal circumstances. Evidence from studies using experimental diets have shortcomings because of their short duration and selection of highly-motivated subjects and because the outcomes can be easily influenced by the choice of foods to be used in the intervention. Of the observational studies, many have severe methodological shortcomings, e.g. ecological studies, cross-sectional surveys and classical cohort studies in which the baseline diet is linked to subsequent weight development over long periods of time. Longitudinal studies with repeated measurements in which changes in diet and physical activity are linked to changes in weight are probably the most informative, but these studies are relatively rare. There is a great interest in interventions that are effective and efficient for the prevention of obesity. Many countries and research funding agencies seem to show a strong tendency to develop interventions for children and adolescents exclusively. It can be easily shown, however, that intervention programmes are much more likely to be cost-effective in older adults than in children, which indicates that adults should not be neglected as target populations for obesity prevention. Obesity prevention should follow a life-course approach, as currently recommended for non-communicable diseases in general by the WHO.

Metabolic and physiological effects of ingesting extracts of bitter orange, green tea and guarana at rest and during treadmill walking in overweight males

OBJECTIVE

This study examined the acute effects of ingesting a widely used commercial formula containing extracts of bitter orange, green tea and guarana (Gx) on the metabolic rate and substrate utilisation in overweight, adult males at rest (study 1) and during treadmill walking (study 2).

SUBJECTS

Two different groups of 10 sedentary males with more than 20% body fat participated in studies 1 and 2.

DESIGN

In each study, subjects participated in two experimental trials during which they were given two 500 mg capsules containing either Gx or a placebo (P) in a counterbalanced double-blind manner. Doses of the main active ingredients were 6 mg of synephrine, 150 mg caffeine and 150 mg catechin polyphenols.

MEASUREMENTS

In study 1, subjects completed 7 h supine rest with baseline measures taken during the first hour, with expired gases, blood pressure, heart rate and venous blood being collected every 30 min for the remaining 6 h following ingestion of Gx or P. In study 2, subjects exercised for 60 min at 60% heart rate reserve following ingestion of Gx or P 1 h previously. Venous blood samples were collected twice at rest and at 5, 10, 15, 20, 30, 40, 50 and 60 min, with expired gas measurements taken at 4, 9, 14, 19, 29, 39, 49 and 59 min. In both studies, venous blood was analysed for NEFA, glycerol, glucose and lactate concentrations, while expired gases were used to calculate ATP production from carbohydrate and NEFA, as well as the total substrate utilised.

RESULTS AND CONCLUSION

The results did not show any significant effect of Gx ingestion on total ATP utilisation during 6 h rest or during 60 min treadmill walking. Changes were observed in the relative contributions of CHO and NEFA oxidation to ATP production in both studies, such that there was an increase in ATP production from CHO and a decrease from NEFA. The increase in CHO oxidation was shown to be as high as 30% at rest.

Differences in short-term metabolic responses to a lipid load in lean (resistant) vs obese (susceptible) young male subjects with habitual high-fat consumption

OBJECTIVE

To determine the role of macronutrients oxidation ability in the postprandial response to a high lipid load in the mechanisms conferring resistance or susceptibility to obesity.

SUBJECTS AND DESIGN

Nine lean and nine obese young male subjects with habitual similar high-fat intake (>40 % of energy) and comparable physical activity were selected and categorized as 'resistant', those who remained lean (body mass index (BMI) <25 kg/m2), and 'susceptible', those who were obese (BMI>30 kg/m2). Fasting blood samples were taken for the evaluation of blood metabolic and hormonal variables. Resting metabolic rate (RMR) and substrates oxidation were measured by indirect calorimetry, in the fasting state and every 30 min for 3 h after a rich lipid meal (fat 94.7%) supplied to cover the 50% of the volunteers energy requirements. The study was performed at the Metabolic Unit of the University of Navarra.

RESULTS

Fasting RMR and lipid oxidation were higher in obese-susceptible subjects. However, similar values were found in both groups after adjustment for fat mass and free fat mass. The cumulative postprandial fat oxidation was also similar in both groups (despite having different tissue metabolic activity), whereas cumulative carbohydrate oxidation was lower in the obese-susceptible group. The thermic effect of food (% of dietary induced thermogenesis) was lower (P<0.05) in the susceptible-obese subjects. The energy and fat balance were more positive in the obesity-susceptible individuals after the high fat load, who also showed higher fasting homeostatic model assessment index, low-density lipoprotein-cholesterol and triacylglyceride levels, hyperleptinemia and hypoadiponectinemia.

CONCLUSION

Lean-resistant individuals came closer to achieving fat balance than obese-susceptible subjects. These metabolic and hormonal differences are probably genetically determined.

Substrate-energy metabolism and metabolic risk factors for cardiovascular disease in relation to fetal growth and adult body composition

The effect of fetal programming on intermediary metabolism is uncertain. Therefore, we examined whether fetal programming affects oxidative and nonoxidative macronutrient metabolism and the prevalence of the metabolic syndrome in adult life. Healthy older men, aged 64-72 years, with either a lower birth weight (LBW, <or=25th %ile; n = 16) or higher birth weight (HBW, >or=75th %ile; n = 13) had measurements of 1) net oxidative metabolism using indirect calorimetry before and for 6 h after a mixed meal (3,720 kJ) and 2) postprandial oxidation of exogenous [13C]palmitic acid. Body composition was measured using dual-energy X-ray absorptiometry. After adjustment for current weight and height, the LBW group had a lower resting energy expenditure (REE) in the preprandial (4.01 vs. 4.54 kJ/min, P = 0.015) and postprandial state (4.60 vs. 5.20 kJ/min, P = 0.004), and less fat-free mass than the HBW group. The BW category was a significant, independent, and better predictor of REE than weight plus height. There were no significant differences between groups in net oxidative and nonoxidative macronutrient (protein, fat, carbohydrate) metabolism (or of exogenous [13C]palmitate) or in the prevalence of the metabolic syndrome, which was present almost twice as commonly in the LBW than in the HBW group. The study suggests that fetal programming affects both pre- and postprandial EE in older life by mechanisms that are at least partly related to the mass of the fat-free body. BW was found to be a significant predictor of REE that was independent of adult weight plus height.

Energy metabolism and oxidative stress: impact on the metabolic syndrome and the aging process

Aging can be defined as a progressive decline in the ability of the organism to resist stress, damage, and disease. Although there are currently over 300 theories to explain the aging phenomenon, it is still not well understood why organisms age and why the aging process can vary so much in speed and quality from individual to individual. The oxidative stress hypothesis is one of the prevailing theories of aging. This theory states that free radicals produced during cellular respiration damage lipids, proteins, and DNA thereby accelerating the aging process and increasing disease risk. Under normal conditions, the electron transport chain is the primary producer of the superoxide anion, which is precursor to other highly reactive species such as hydrogen peroxide and the hydroxyl radical. Oxidative stress accumulates when prooxidants overwhelm the antioxidant defense mechanisms. This is dependent on a number of factors including free radical production, susceptibility of tissue to stress, and strength of the defense and repair system. Oxidative stress has been implicated in a number of chronic disease states usually grouped under the umbrella of the metabolic syndrome and is thought to contribute to the aging process. It has been hypothesized that the production of free radicals is dependent on resting metabolic rate and this may have an impact on the aging process. However, other factors, such as mitochondrial function, may be important in the production of free radicals and the subsequent effect on aging and disease states.