Factors influencing the composition of the weight lost by obese patients on a reducing diet

Development and validation of prognostic models to estimate body weight loss in overweight and obese people

Introduction

Background: predicting weight loss outcomes from information collected from subjects before they start a weight management program is an objective strongly pursued by scientists who study energy balance. Objective: to develop and validate two prognostic models for the estimation of final body weight after a six-month intervention period. Material and methods: the present work was developed following the TRIPOD standard to report prognostic multivariable prediction models. A multivariable linear regression analysis was applied to 70 % of participants to identify the most relevant variables and develop the best prognostic model for body weight estimation. Then, 30 % of the remaining sample was used to validate the model. The study involved a 6-month intervention based on 25-30 % caloric restriction and exercise. A total of 239 volunteers who had participated in the PRONAF study, aged 18 to 50 years, with overweight or obesity (body mass index: 25-34.9 kg/m2), were enrolled. Body composition was estimated by dual-energy X-ray absorptiometry (DXA) and by hand-to-foot bioelectrical impedance (BIA) analysis. Results: prognostic models were developed and validated with a high correlation (0.954 and 0.951 for DXA and BIA, respectively), with the paired t-tests showing no significant differences between estimated and measured body weights. The mean difference, standard error, and 95 % confidence interval of the DXA model were 0.067 ± 0.547 (-1.036-1.170), and those of the BIA model were -0.105 ± 0.511 (-1.134-0.924). Conclusions: the models developed in this work make it possible to calculate the final BW of any participant engaged in an intervention like the one employed in this study based only on baseline body composition variables.

Thermogenic and metabolic antiobesity drugs: rationale and opportunities

Antiobesity drugs that target peripheral metabolism may avoid some of the problems that have been encountered with centrally acting anorectic drugs. Moreover, if they cause weight loss by increasing fat oxidation, they not only address a cause of obesity but also should promote loss of fat rather than lean tissue and improve insulin sensitivity. Weight loss may be slow but more sustained than with anorectic drugs, and thermogenesis may be insufficient to cause any discomfort. Some thermogenic approaches are the activation of adrenergic, thyroid hormone or growth hormone receptors and the inhibition of glucocorticoid receptors; the modulation of transcription factors [e.g. peroxisome proliferator-activated receptor delta (PPARdelta) activators] or enzymes [e.g. glutamine fructose-6-phosphate amidotransferase (GFAT) inhibitors] that promote mitochondrial biogenesis, and the modulation of transcription factors (PPAR alpha activators) or enzymes (AMP-activated protein kinase) that promote fatty acid oxidation. More surprisingly, studies on genetically modified animals and with enzyme inhibitors suggest that inhibitors of fatty acid synthesis [e.g. ATP citrate lyase, fatty acid synthase, acetyl-CoA carboxylase (ACC)], fatty acid interconversion [stearoyl-CoA desaturase (SCD)] and triglyceride synthesis (e.g. acyl-CoA : diacylglycerol acyltransferase) may all be thermogenic. Some targets have been validated only by deleting genes in the whole animal. In these cases, it is possible that deletion of the protein in the brain is responsible for the effect on adiposity, and therefore a centrally penetrant drug would be required. Moreover, whilst a genetically modified mouse may display resistance to obesity in response to a high fat diet, it requires a tool compound to demonstrate that a drug might actually cause weight loss. Even then, it is possible that differences between rodents and humans, such as the greater thermogenic capacity of rodents, may give a misleading impression of the potential of a drug.

Increasing the protein content in a carbohydrate-free diet enhances fat loss during 35% but not 75% energy restriction in rats

The purpose of the present study was to test the influence of the amount of protein in a carbohydrate-free diet during a weight reducing program using severe (75%) or more moderate (35%) energy restriction in rats. In Expt. 1, 3 groups (n = 6) consumed ad libitum a high-carbohydrate, low-fat diet [P21C69L10 containing 21% of energy as protein (P21), 69% carbohydrate (C69) and 10% lipids (L10)], a high-carbohydrate, high-fat diet (P21C34L45), or a carbohydrate-free, high-fat, high-protein diet (P55L45). In Expt. 2, 7 groups (n = 7) were studied. For 20 d, groups 1-4 consumed ad libitum diets containing macronutrients at the proportions indicated in their designations [P14C56L30 (control diet), P30L70, P50L50, and P90L10]. Groups 5-7 were pair-fed the same diets at the level of the spontaneous intake of the P90L10 group on the previous day (35% energy restriction). In Expt. 3, 5 groups (n = 7) were fed 1 of the following diets for 20 d. Group 1 consumed the control diet (P14C56L30) ad libitum. Groups 2-5 were energy restricted to 25% of the daily energy intake of group 1 with diets varying in their protein and lipid concentrations (P14C56L30, P50L50, P70L30, and P90L10). A high-fat content in the diet devoid of carbohydrate did not increase energy intake and body adiposity and neither body weight nor body composition was significantly affected by the protein to lipid ratio when energy restriction was 75%; however, a protein content > 50% preserved lean body mass at the expense of fat mass when energy restriction was 35%. Our results show that the absence of carbohydrates from the diet induces a low energy intake and the preferential deposition of protein.

Weight loss and body-composition changes in men and women infected with HIV

BACKGROUND

The nature of body-composition changes in HIV-associated weight loss is unclear.

OBJECTIVE

We examined the relation between the initial percentage of body fat and the composition of weight loss in men and women with HIV infection.

DESIGN

HIV-positive adults were seen at semiannual clinic visits, at which time weight, fat, and fat-free mass were determined. The unit of analysis was the person-interval.

RESULTS

Five hundred fifty-one persons contributed 2266 intervals of data, of which 311 (14%) were intervals in which weight loss was >/= 5% of initial (start of interval) weight. Of these, 208 (67%) intervals met the criteria for analysis (123 from men and 85 from women). Loss of fat-free mass was dependent on the initial percentage of body fat in the men with < 32% body fat. A plot of the initial percentage of body fat compared with loss of fat-free mass (kg) suggested a nonlinear relation over the range of body fat examined. There was no clear relation between the initial percentage of body fat and loss of fat-free mass in the women.

CONCLUSIONS

In men with HIV-associated weight loss, the weight lost as fat-free mass depends on the initial percentage of body fat at low levels of body fat but appears to be independent of initial percentage of body fat at high levels of body fat. In women with HIV-associated weight loss who have normal-to-high body fat stores, loss of fat-free mass is independent of the initial percentage of body fat.

Sexual dimorphism in the energy content of weight change

BACKGROUND

The energy content of weight change is assumed to be sex- and age-neutral at 3,500 kcal/pound or 32.2 MJ/kg.

OBJECTIVES

As sexual dimorphism in body composition generally exists in mammals, the primary hypothesis advanced and tested was that the energy content of weight change differs between men and women.

DESIGN

The energy content of 129 adult men and 287 women was measured by neutron activation analysis. Cross-sectional energy content prediction models were developed and then evaluated in two longitudinal samples: one that used the same methods in 26 obese women losing weight; and the other a compilation of 18 previously reported weight change-body composition studies.

RESULTS

Multiple regression modeling identified weight, sex, age and height as total energy content predictor variables with significant sex x weight (P<0.001) and age x weight (P<0.001) interactions; total model r(2) and s.e.e. were 0.89 and 107.3 MJ, respectively. The model's predictive value was supported in both longitudinal evaluation samples. Model calculations using characteristics of representative adults gaining or losing weight suggested that the energy content of weight change in women (approximately 30.1-32.2 MJ/kg) is near to the classical value of 32.2 MJ/kg and that in men the value is substantially lower, approximately 21.8-23.8 MJ/kg. The predicted energy content of weight change increases by about 10% in older (age approximately 70 y) vs younger (approximately 35 y) men and women.

CONCLUSIONS

Sexual dimorphism and age-dependency appears to exist in the estimated energy content of weight change and these observations have important clinical and research implications.

beta(3)-Adrenoceptor agonists: potential, pitfalls and progress

beta(3)-Adrenoceptor agonists are very effective thermogenic anti-obesity and insulin-sensitising agents in rodents. Their main sites of action are white and brown adipose tissue, and muscle. beta(3)-Adrenoceptor mRNA levels are lower in human than in rodent adipose tissue, and adult humans have little brown adipose tissue. Nevertheless, beta(3)-adrenoceptors are expressed in human white as well as brown adipose tissue and in skeletal muscle, and they play a role in the regulation of energy balance and glucose homeostasis. It is difficult to identify beta(3)-adrenoceptor agonist drugs because the pharmacology of both beta(3)- and beta(1)-adrenoceptors can vary; near absolute selectivity is needed to avoid beta(1/2)-adrenoceptor-mediated side effects and selective agonists tend to have poor oral bioavailability. All weight loss is lipid and lean may actually increase, so reducing weight loss relative to energy loss. beta(3)-adrenoceptor agonists have a more rapid insulin-sensitising than anti-obesity effect, possibly because stimulation of lipid oxidation rapidly lowers intracellular long-chain fatty acyl CoA and diacylglycerol levels. This may deactivate those protein kinase C isoenzymes that inhibit insulin signalling.

Weight and body composition in a cohort of HIV-positive men and women

OBJECTIVE

At issue is whether weight loss in HIV infection is a cachectic process, characterised by loss of lean body mass with conservation of fat, or a process of starvation. We present data on body composition from 516 persons at different stages of HIV infection as determined by CD4 counts.

DESIGN

Cross-sectional analyses of body composition in relation to CD4 count.

SETTING

The baseline data from a prospective cohort study of outcomes in HIV/AIDS in relation to nutritional status in Boston, Massachusetts, USA.

SUBJECTS

: The first 516 subjects with HIV/AIDS to enroll in the study.

RESULTS

Differences in weight in relation to CD4 counts were present only at CD4 counts of 600 or less (slope below : 1.9 kg per 100 CD4 cells, On average, 68% of the difference in weight over CD4 counts was fat (slope: 1.3 kg fat per 100 CD4 cells,

CONCLUSIONS

This cross-sectional analysis suggests that weight loss consists principally of fat loss in those persons with adequate fat stores. This observation will need to be confirmed in longitudinal analyses.

Caloric restriction mimetics: physical activity and body composition changes

As the only paradigm that has consistently increased life span and inhibited the onset and/or progression of disease, dietary restriction has multiple effects on a variety of organ systems. In this brief review, the goal of the panel was to attempt to understand the role of changes in physical activity and body composition as possible modulators of the life span in experimental animals and humans. We focus on whether changes in exercise behavior and body composition produce similar changes as those found in dietary restriction and whether these changes can be used to either replace or enhance the beneficial effects of dietary restriction. The complexity of the two stimuli is emphasized in our report, with suggestions offered on how to better interpret existing research. Our panel briefly examines evidence in experimental animals and humans about the specific contributions of each of these factors to altering life span and age-related pathologies. We also discuss additional animal studies and/or human intervention studies that could be performed to clarify these issues. Finally, we provide suggested avenues for future research in this area of changes in physical activity and body composition as dietary restriction mimetics.

Effect of age on protein conservation during very-low-energy diet in obese Sprague-Dawley rats

OBJECTIVE

To examine the effect of age on body protein losses occurring during severe energy restriction in obesity.

RESEARCH METHODS AND PROCEDURES

Weanling (young) Sprague-Dawley rats (YR) were fed a high fat (35% energy) diet (HFD) until mean body weight approached that of a group of chow-fed retired breeder (aged) rats (AR). Both groups were then fed HFD for an additional 2 weeks, after which selected controls from YR and AR groups were killed for baseline carcass analysis. Remaining rats were fed a very-low-energy diet (VLED, 33% kcal of HFD) for 3 weeks and then killed for carcass analysis.

RESULTS

YR had greater fat stores before VLED, and lost proportionately more fat and less protein during VLED than did AR. Weight loss composition during VLED was 66.7% fat, 11.1% protein, and 22.2% water in YR, and 39.4% fat, 26.2% protein, and 34.3% water in AR. Greater YR fat loss during VLED (70.6+/-30.4 vs. 32.6+/-29.1 g in AR; mean+/-SD) was paralleled by significantly larger decreases in epididymal and retroperitoneal fat pad weights, mean adipocyte size, and lipoprotein lipase activity. Greater protein loss in AR (21.6+/-13.9 g vs. 11.8+/-10.7 g in YR) coincided with larger decreases in visceral organ weights and serum thyroxine and triiodothyronine. Energy expenditure changes during VLED were similar between groups.

DISCUSSION

Dietary obese young rats appear better able than aged rats to conserve body protein while losing body fat during severe energy restriction.

Serial measurements of body composition in obese subjects during a very-low-energy diet (VLED) comparing bioelectrical impedance with hydrodensitometry

Bioelectrical impedance analysis (BIA) is a convenient, inexpensive, and noninvasive technique for measuring body composition. BIA has been strongly correlated with total body water (TBW) and also has been validated against hydrodensitometry (HD). The accuracy and clinical utility of BIA and HD during periods of substantial weight loss remain controversial. We measured body composition in moderately and severely obese patients serially using both methods during a very-low-energy diet (VLED). Mean initial weight in these patients was 116 (+/-30) kg (range, 74-196 kg). Mean weight loss was 24 (+/-13) kg with a decrease in fat mass (FM) by HD of kg (p < 0.001) and a decrease in fat-free mass (FFM) of 3.6 kg (p < 0.05). Loss of FFM is best predicted by the rate (kg/wk) of weight loss (r2 = 0.86, p < 0.0001). FFM, as predicted from BIA equations, was highly correlated with FFM as estimated by HD during all testing sessions (r = 0.92-0.98). Although highly correlated, BIA overestimated FFM relative to HD and this difference appeared to be more pronounced for taller patients with greater truncal obesity. Although the discrepancy was no greater during weight-loss treatment, the level of disagreement was considerable. Therefore, the two methods cannot be used interchangeably to monitor relative changes in body composition in patients with obesity during treatment with VLED. The discrepancy between BIA and HD may be caused by body mass distribution considerations and by perturbations in TBW which affect the hydration quotient for FFM (BIA) and/or which affect the density constants for FFM and FM (HD).

Changes in the body composition of cats during weight reduction by controlled dietary energy restriction

Thirteen overweight domestic short-haired cats were fed a commercial low calorie diet for 18 weeks at an energy intake to lose weight; they lost an average of 18.1 per cent of their starting weight. An evaluation of their body composition by dual energy x-ray absorptiometry before and after the study suggested that most of the weight lost was composed of fat. The cats' lean bodyweight did not change significantly, but increased as a proportion of total bodyweight.

Effects of weight loss by diet alone or combined with aerobic exercise on body composition in older obese men

The effects of weight loss induced by hypocaloric diet (HD) alone or combined with aerobic exercise (AEX+HD) on body composition were compared in 61 sedentary obese men aged 60.6 +/- 1.0 years (mean +/- SEM). Twenty-three subjects in the AEX+HD intervention and 28 subjects in the HD intervention lost a similar amount of body weight (range, 3 to 22 kg). Fifteen men underwent no intervention and served as controls (CON). All groups were of similar body composition at baseline. The HD group decreased caloric intake for 10 months, whereas the AEX+HD group combined HD with AEX (3 times per week) for 10 months. The HD and AEX+HD groups had significant and comparable reductions in body weight (9.3 +/- 0.8 v 8.1 +/- 0.6 kg), fat mass (6.8 +/- 0.5 v 6.7 +/- 0.5 kg), and fat-free mass (2.1 +/- 0.3 v 1.3 +/- 0.3 kg; all P < .05). None of the variables changed significantly in the CON group. Regression lines depicting the relationship between the loss in fat-free mass and the decrease in body weight did not differ significantly in either slope or intercept between the treatment groups. These results suggest that in older obese men, hypocaloric dieting combined with AEX training does not attenuate the loss in fat-free mass that occurs during weight loss by hypocaloric dieting alone.

Protein sparing during treatment of obesity: ketogenic versus nonketogenic very low calorie diet

Although it is generally agreed that both ketogenic and nonketogenic very low calorie diets promote weight reduction, there is no consensus on a preference of one diet over the other in regard to protein sparing. In the present study, we compared the effects of isocaloric (600 kcal/d) and isonitrogenous (8 g nitrogen/d) ketogenic (low carbohydrate) and nonketogenic diets on parameters of protein and amino acid metabolism, in 16 morbidly obese women maintained on these diets for 4 weeks while confined to a metabolic ward. Cumulative urinary nitrogen excretion (g/4 wk) was significantly (P less than .01) greater (248 +/- 6 v 207 +/- 12, mean +/- SEM, n = 8), and cumulative nitrogen balance significantly (P less than .02) more negative (-50.4 +/- 4.4 v -18.8 +/- 5.7), during treatment with the ketogenic than with the nonketogenic diet. Plasma leucine concentration (mumol/L) was significantly higher (P less than .05) during treatment with the ketogenic than with the nonketogenic diet at day 14 (210 +/- 17 v 150 +/- 8), but not at day 28 (174 +/- 9 v 148 +/- 8). Whole-body rates of leucine oxidation (mmol/h) were significantly higher (P less than .05) during treatment with the ketogenic than with the nonketogenic diet at day 14 (1.29 +/- 0.20 v 0.92 +/- 0.10) and at day 28 (1.00 +/- 0.16 v 0.75 +/- 0.10). Conversely, proteolysis, as measured by leucine turnover rate and urinary excretion of 3-methylhistidine, was not significantly different between the diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Management strategies for weight control. Eating, exercise and behaviour

Obesity is a major health and social problem worldwide for which no single satisfactory treatment exists. Because of the prevalence of the disease, numerous therapeutic strategies have been attempted--often unsuccessfully. Weight loss programmes based on dietary restriction of caloric intake and nutritional education, exercise, surgical (gastroplasty, gastric bypass) and procedural (gastric balloon, waist cord, jaw wiring, liposuction) intervention and pharmacotherapy (appetite suppressants, thermogenic agents, bulking agents) used alone or in combination, have produced weight loss in the short to medium term; however, weight is generally regained on discontinuation of treatment. Behaviour modification programmes appear to offer the highest success rate in the long term. Weight loss is not rapid, although losses of 10 to 15 kg have been achieved after 6 months, and this may be increased when behaviour modification therapy is combined with more aggressive treatments such as severe caloric restriction or jaw wiring. Behaviour modification is particularly beneficial in special patient groups such as the obese elderly, children or adolescents, and disabled patients. Thus, although it appears that each of the treatments developed for the management of obese patients has its place, the cornerstone of therapy for most patients remains a programme of dietary restriction, combined with exercise and behaviour modification.

Energy expenditure in obesity in fasting and postprandial state

Resting metabolic rate (RMR) was determined in 10 obese and 10 nonobese women after an overnight fast and for 3 h after the ingestion of an 800-kcal liquid meal. In the fasting state, absolute energy expenditure in the obese (4.8 +/- 0.2 kJ/min) was 25% greater than in the nonobese (P less than 0.005), but was comparable with the nonobese when expressed in relation to body surface area or lean body mass and was reduced by 20% when expressed per kilogram body weight3/4 (P less than 0.005). Meal ingestion resulted in a 14-16% increase in RMR (postprandial thermogenesis) that was similar in the two groups, so that absolute energy expenditure in the obese remained 22-25% higher than in the nonobese throughout the postprandial period. The estimated overall (fasting and postprandial) increase in resting caloric expenditure in the obese as compared with the nonobese was 350-375 kcal/day.

The effect of meal frequency and protein concentration on the composition of the weight lost by obese subjects

1. Nitrogen balance, weight loss and resting metabolic rate were measured in thirty-eight obese inpatients on 3.4 MJ (800 kcal)/d diets over 3 weeks. 2. All subjects were fed on 13% protein-energy in three meals/d for the first week. 3. In weeks 2 or 3, using a cross-over design, ten subjects were fed on 15 or 10% protein-energy as three meals/d; fourteen subjects were fed on five or one meal/d with 13% protein-energy; and fourteen subjects were fed on 15% protein-energy as five meals/d or 10% protein-energy as one meal/d. 4. N loss was least on the high-protein week and frequent-meal week: the largest difference was found when these effects were combined (P less than 0.001). 5. When protein-energy was held constant at 13% N loss decreased significantly (P less than 0.01) between week 2 and 3, but when the protein-energy was manipulated there was no significant N conservation in the third week. This suggests that the protein:energy value is more important than meal frequency in the preservation of lean tissue. 6. Weight loss was also least on the 'high-protein' week and 'frequent-meal' week, but this result reached significance only when the effects were combined (P less than 0.05). 7. Resting metabolic rate decreased with time but was not significantly altered by the dietary regimens. 8. Therefore, during the first 3 weeks at an intake of 3.4 MJ/d, a diet with a high-protein concentration, fed as frequent small meals, is associated with better preservation of lean tissue than an isoenergetic diet with lower-protein concentration fed as fewer meals. There was no evidence that meal frequency or protein concentration affect the rate of fat loss.