Dietary fat oxidation as a function of body fat

Effects of exercise conducted prior to phenylketonuria-type meal on appetite, satiety hormones and energy expenditure: a randomised cross-over trial

BACKGROUND/OBJECTIVES

Individuals with phenylketonuria (PKU) are at increased risk for obesity, possibly due to reduced satiety induced by a PKU diet that is low protein and high carbohydrate. It is unclear how exercise alters postprandial satiety after a PKU-like meal. The objective was to examine changes in postprandial satiety, satiety hormone concentrations, energy expenditure and substrate oxidation in response to acute treadmill exercise following a PKU-like meal.

SUBJECTS/METHODS

Sixteen males (mean age [±SD]: 26.5 ± 4.8 years; BMI: 23.7 ± 3.2 kg/m2) participated in a randomized cross-over trial with two conditions: exercise and control. Both trials involved consuming a PKU-like meal comprising naturally low-protein foods, a special low-protein food and a protein substitute. In the exercise trial, participants exercised at 60% of maximal oxygen uptake for 1 h before the meal; in the control trial, they rested. Satiety agents (peptide YY [PYY], glucagon-like peptide-1 [GLP-1] and growth differentiation factor-15 [GDF-15]), appetite, energy expenditure, fat oxidation and carbohydrate oxidation were measured.

RESULTS

Mean (±SE) appetite and postprandial PYY and GLP-1 concentrations were unaffected by exercise (P ≥ 0.279). However, GDF-15 was higher in the exercise trial (control: 288 ± 25 pg/mL vs. exercise: 322 ± 24 pg/mL; P = 0.002). Exercise increased fat oxidation (P = 0.013) and decreased carbohydrate oxidation post-meal (P = 0.022), with concomitantly lower RER (P = 0.005). Energy expenditure rose during exercise (P < 0.001), but no difference occurred postprandially (P = 0.543).

CONCLUSIONS

Acute exercise prior to a PKU-like meal does not affect postprandial GLP-1 and PYY concentrations compared to control but GDF-15 was increased and RER was reduced, potentially improving appetite regulation.

Stevioside Enhances the Anti-Adipogenic Effect and β-Oxidation by Activating AMPK in 3T3-L1 Cells and Epididymal Adipose Tissues of db/db Mice

Stevioside, the primary sweetener in stevia, is a glycoside with numerous beneficial biological activities. However, its anti-adipogenic effects on tissue differentiation and adipose tissues remain to be thoroughly investigated. In this study, the anti-adipogenic effects of stevioside during the differentiation of 3T3-L1 cells and epididymal adipose tissues of db/db mice were investigated by measuring the lipid droplets stained with Oil Red O and an immunoblot assay. Immunoblot analysis revealed that stevioside downregulated the expression of peroxisome proliferator-activated receptor-gamma (PPARγ), sterol regulatory element-binding protein-1c (SREBP-1c), CCAAT/enhancer-binding protein alpha (C/EBPα), and fatty acid synthase (FAS). Additionally, the protein expression of carnitine palmitoyltransferase 1 (CPT1), silent mating type information regulation 2 homolog 1 (SIRT1), and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) increased following treatment with stevioside. Furthermore, stevioside increased the phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC), both in vitro and in vivo. The activity of AMPK in stevioside-treated 3T3-L1 cells was further confirmed using agonists and antagonists of AMPK signaling. Our data indicate that stevioside ameliorates anti-adipogenic effects and promotes β-oxidation in adipocytes by activating AMPK-mediated signaling. The results of this study clearly demonstrated the inhibitory effect of stevioside on the differentiation of adipocytes and the reduction of lipid accumulation in the epididymal adipose tissues of db/db mice.

Key Causes and Contributors of Obesity: A Perspective

Obesity is a disease with several potential causes and contributors. This article provides a focused overview of key known causes of obesity and factors that contribute to obesity. Obesity ultimately results from impaired energy storage mechanisms, such as dysregulation of hunger, satiety, digestion, fat storage, and metabolic rate. In addition, myriad contributors promote its expression, including dietary factors, sleep quality and duration, psychological health and well-being, and tobacco cessation, among others. This article concludes with a discussion of the clinical relevance of causes and contributors in obesity prevention and treatment, which is paramount to providing effective, individualized clinical management.

Cell-Specific "Competition for Calories" Drives Asymmetric Nutrient-Energy Partitioning, Obesity, and Metabolic Diseases in Human and Non-human Animals

The mammalian body is a complex physiologic “ecosystem” in which cells compete for calories (i.e., nutrient-energy). Axiomatically, cell-types with competitive advantages acquire a greater number of consumed calories, and when possible, increase in size and/or number. Thus, it is logical and parsimonious to posit that obesity is the competitive advantages of fat-cells (adipocytes) driving a disproportionate acquisition and storage of nutrient-energy. Accordingly, we introduce two conceptual frameworks. Asymmetric Nutrient-Energy Partitioning describes the context-dependent, cell-specific competition for calories that determines the partitioning of nutrient-energy to oxidation, anabolism, and/or storage; and Effective Caloric Intake which describes the number of calories available to constrain energy-intake via the inhibition of the sensorimotor appetitive cells in the liver and brain that govern ingestive behaviors. Inherent in these frameworks is the independence and dissociation of the energetic demands of metabolism and the neuro-muscular pathways that initiate ingestive behaviors and energy intake. As we demonstrate, if the sensorimotor cells suffer relative caloric deprivation via asymmetric competition from other cell-types (e.g., skeletal muscle- or fat-cells), energy-intake is increased to compensate for both real and merely apparent deficits in energy-homeostasis (i.e., true and false signals, respectively). Thus, we posit that the chronic positive energy balance (i.e., over-nutrition) that leads to obesity and metabolic diseases is engendered by apparent deficits (i.e., false signals) driven by the asymmetric inter-cellular competition for calories and concomitant differential partitioning of nutrient-energy to storage. These frameworks, in concert with our previous theoretic work, the Maternal Resources Hypothesis, provide a parsimonious and rigorous explanation for the rapid rise in the global prevalence of increased body and fat mass, and associated metabolic dysfunctions in humans and other mammals inclusive of companion, domesticated, laboratory, and feral animals.

Perspective: A Historical and Scientific Perspective of Sugar and Its Relation with Obesity and Diabetes

Fructose-containing added sugars, such as sucrose and high-fructose corn syrup, have been experimentally, epidemiologically, and clinically shown to be involved in the current epidemics of obesity and diabetes. Here we track this history of intake of sugar as it relates to these epidemics. Key experimental studies that have identified mechanisms by which fructose causes obesity and diabetes are reviewed, as well as the evidence that the uricase mutation that occurred in the mid-Miocene in ancestral humans acted as a "thrifty gene" that increases our susceptibility for fructose-associated obesity today. We briefly review recent evidence that obesity can also be induced by nondietary sources of fructose, such as from the metabolism of glucose (from high-glycemic carbohydrates) through the polyol pathway. These studies suggest that fructose-induced obesity is driven by engagement of a "fat switch" and provide novel insights into new approaches for the prevention and treatment of these important diseases.

Daily stressors, past depression, and metabolic responses to high-fat meals: a novel path to obesity

BACKGROUND

Depression and stress promote obesity. This study addressed the impact of daily stressors and a history of major depressive disorder (MDD) on obesity-related metabolic responses to high-fat meals.

METHODS

This double-blind, randomized, crossover study included serial assessments of resting energy expenditure (REE), fat and carbohydrate oxidation, triglycerides, cortisol, insulin, and glucose before and after two high-fat meals. During two separate 9.5-hour admissions, 58 healthy women (38 breast cancer survivors and 20 demographically similar control subjects), mean age 53.1 years, received either a high saturated fat meal or a high oleic sunflower oil meal. Prior day stressors were assessed by the Daily Inventory of Stressful Events.

RESULTS

Greater numbers of stressors were associated with lower postmeal REE (p = .008), lower fat oxidation (p = .04), and higher insulin (p = .01), with nonsignificant effects for cortisol and glucose. Women with prior MDD had higher cortisol (p = .008) and higher fat oxidation (p = .004), without significant effects for REE, insulin, and glucose. Women with a depression history who also had more stressors had a higher peak triglyceride response than other participants (p = .01). The only difference between meals was higher postprandial glucose following sunflower oil compared with saturated fat (p = .03).

CONCLUSIONS

The cumulative 6-hour difference between one prior day stressor and no stressors translates into 435 kJ, a difference that could add almost 11 pounds per year. These findings illustrate how stress and depression alter metabolic responses to high-fat meals in ways that promote obesity.

The childhood obesity epidemic as a result of nongenetic evolution: the maternal resources hypothesis

Over the past century, socioenvironmental evolution (eg, reduced pathogenic load, decreased physical activity, and improved nutrition) led to cumulative increments in maternal energy resources (ie, body mass and adiposity) and decrements in energy expenditure and metabolic control. These decrements reduced the competition between maternal and fetal energy demands and increased the availability of energy substrates to the intrauterine milieu. This perturbation of mother-conceptus energy partitioning stimulated fetal pancreatic β-cell and adipocyte hyperplasia, thereby inducing an enduring competitive dominance of adipocytes over other tissues in the acquisition and sequestering of nutrient energy via intensified insulin secretion and hyperplastic adiposity. At menarche, the competitive dominance of adipocytes was further amplified via hormone-induced adipocyte hyperplasia and weight-induced decrements in physical activity. These metabolic and behavioral effects were propagated progressively when obese, inactive, metabolically compromised women produced progressively larger, more inactive, metabolically compromised children. Consequently, the evolution of human energy metabolism was markedly altered. This phenotypic evolution was exacerbated by increments in the use of cesarean sections, which allowed both the larger fetuses and the metabolically compromised mothers who produced them to survive and reproduce. Thus, natural selection was iatrogenically rendered artificial selection, and the frequency of obese, inactive, metabolically compromised phenotypes increased in the global population. By the late 20th century, a metabolic tipping point was reached at which the postprandial insulin response was so intense, the relative number of adipocytes so large, and inactivity so pervasive that the competitive dominance of adipocytes in the sequestering of nutrient energy was inevitable and obesity was unavoidable.

High fat diets are associated with higher abdominal adiposity regardless of physical activity in adolescents; the HELENA study

BACKGROUND & AIMS

Failure to attain fat balance may contribute to obesity development even without excessive energy intake. The objective of this study was to examine the associations of dietary macronutrient distribution with abdominal adiposity in adolescents and to evaluate whether these relationships were attenuated by physical activity.

METHODS

A total of 224 Spanish adolescents (51% females, 14.9 ± 1.2 years) were included in the study. Abdominal adiposity in three regions, truncal and total body fat mass (FM) and lean mass (LM) were measured by dual-energy X-ray absorptiometry and thereafter FM index (FMI = FM/height(2)) and FMI/LMI ratio were calculated. The energy derived from fat intake was assessed by two non-consecutive 24 h recalls. Total physical activity (PA) and time spent in moderate-to-vigorous PA (MVPA) and vigorous PA were objectively measured by accelerometry.

RESULTS

We observed that the percent of energy derived from fat intake was significantly associated with FMI and FMI/LMI ratio (Ps = 0.001) and greater amounts of truncal (P = 0.001) and abdominal adiposity in the three regions regardless of age, sex and height (all P ≤ 0.005). The strength of the relationships was not substantially altered by further adjustment for PA, vigorous PA or moderate-to-vigorous PA (Ps ≤ 0.005).

CONCLUSIONS

The percent of energy derived from dietary fat intake is strongly and linearly associated with total, truncal and abdominal adiposity independently of PA in adolescents. These observations implicate the amount of dietary fat intake as a specific risk factor in the excess of abdominal adiposity in adolescence.

The effects of short-term overfeeding on energy expenditure and nutrient oxidation in obesity-prone and obesity-resistant individuals

Objective

The roles that energy expenditure (EE) and nutrient oxidation play in a predisposition for weight gain in humans remains unclear.

Subjects

We measured EE and respiratory exchange ratio (RER) in non-obese obesity prone (OP; n=22) and obesity resistant (OR; n=30) men and women following a eucaloric diet and after 3 days of overfeeding (1.4x basal energy).

Results

Twenty four hour EE, adjusted for fat free mass and sex, measured while consuming a eucaloric diet was not different between OP and OR subjects (2367 ± 80 vs. 2285 ± 98 kcals; p=0.53). Following overfeeding, EE increased in both OP and OR (OP: 2506 ± 63.7, p<0.01; OR: 2386 ± 99 kcals, p<0.05). Overfeeding resulted in an increase in 24h RER (OP: 0.857 ± 0.01 to 0.893 ± 0.01, p=0.01; OR: 0.852 ± 0.01 to 0.886 ± 0.01, p=0.005), with no difference between groups in either the eucaloric or overfeeding conditions (p>0.05). Nighttime RER (~10pm-6:30am) did not change with overfeeding in OR (0.823 ± 0.02 vs. 0.837 ± 0.01, p=0.29), but increased significantly in OP subjects (0.798 ± 0.15 to 0.839 ± 0.15, p<0.05), suggesting that fat oxidation during the night was down-regulated to a greater extent in OP subjects following a brief period of overfeeding, as compared to OR subjects who appeared to maintain their usual rate of fat oxidation. Protein oxidation increased significantly in both OP (p<0.001) and OR (p<0.01) with overfeeding, with no differences between OP and OR.

Conclusion

These results support the idea that overfeeding a mixed diet results in increases in EE and RER, but these increases in EE and RER are likely not responsible for obesity resistance. Adaptive responses to overfeeding that occur during the night may play a role in opposing weight gain.

Treatment of genetically obese mice with the iminosugar N-(5-adamantane-1-yl-methoxy-pentyl)-deoxynojirimycin reduces body weight by decreasing food intake and increasing fat oxidation

Obesity and its associated conditions such as type 2 diabetes mellitus are major causes of morbidity and mortality. The iminosugar N-(5-adamantane-1-yl-methoxy-pentyl)-deoxynojirimycin (AMP-DNM) improves insulin sensitivity in rodent models of insulin resistance and type 2 diabetes mellitus. In the current study, we characterized the impact of AMP-DNM on substrate oxidation patterns, food intake, and body weight gain in obese mice. Eight ob/ob mice treated with 100 mg/(kg d) AMP-DNM mixed in the food and 8 control ob/ob mice were placed in metabolic cages during the first, third, and fifth week of the experiment for measurement of substrate oxidation rates, energy expenditure, activity, and food intake. Mice were killed after 6 weeks of treatment. Initiation of treatment with AMP-DNM resulted in a rapid increase in fat oxidation by 129% (P = .05), a decrease in carbohydrate oxidation by 35% (P = .01), and a reduction in food intake by approximately 26% (P < .01) compared with control mice. Treatment with AMP-DNM decreased hepatic triglyceride content by 66% (P < .01) and, in line with the elevated fat oxidation rates, increased hepatic carnitine palmitoyl transferase 1a expression. Treatment with AMP-DNM increased plasma levels of the appetite-regulating peptide YY compared with control mice. Treatment with AMP-DNM rapidly reduces food intake and increases fat oxidation, resulting in improvement of the obese phenotype. These features of AMP-DNM, together with its insulin-sensitizing capacity, make it an attractive candidate drug for the treatment of obesity and its associated metabolic derangements.

The relationship between substrate metabolism, exercise and appetite control: does glycogen availability influence the motivation to eat, energy intake or food choice?

The way in which metabolic fuels are utilized can alter the expression of behaviour in the interests of regulating energy balance and fuel availability. This is consistent with the notion that the regulation of appetite is a psychobiological process, in which physiological mediators act as drivers of behaviour. The glycogenostatic theory suggests that glycogen availability is central in eliciting negative feedback signals to restore energy homeostasis. Due to its limited storage capacity, carbohydrate availability is tightly regulated and its restoration is a high metabolic priority following depletion. It has been proposed that such depletion may act as a biological cue to stimulate compensatory energy intake in an effort to restore availability. Due to the increased energy demand, aerobic exercise may act as a biological cue to trigger compensatory eating as a result of perturbations to muscle and liver glycogen stores. However, studies manipulating glycogen availability over short-term periods (1-3 days) using exercise, diet or both have often produced equivocal findings. There is limited but growing evidence to suggest that carbohydrate balance is involved in the short-term regulation of food intake, with a negative carbohydrate balance having been shown to predict greater ad libitum feeding. Furthermore, a negative carbohydrate balance has been shown to be predictive of weight gain. However, further research is needed to support these findings as the current research in this area is limited. In addition, the specific neural or hormonal signal through which carbohydrate availability could regulate energy intake is at present unknown. Identification of this signal or pathway is imperative if a casual relationship is to be established. Without this, the possibility remains that the associations found between carbohydrate balance and food intake are incidental.

The use of human tissues and cells in biomedical research: the unusual suspects

There are compelling reasons to search for alternatives to the use of animals in medical and pharmaceutical research. Aside from the obvious animal welfare issues, both the well-established differences between animal models and humans, and the inherent inter-individual variability in human biological responses, indicate that human-based alternatives are urgently required. However, any such alternative must out-perform the animal-based alternative, otherwise there will be little or no uptake and adoption by end-users. Data obtained from inbred animal models is often highly reproducible, and is therefore attractive to researchers in the fields of biomedical and pharmaceutical research. The inter-individual variability observed during human volunteer and human tissue-based studies is often considered to be problematic, and has been highlighted further with the advent of the 'omics' technologies, which generate large biological datasets. However, the variability in both baseline data and response to pharmacological or toxicological challenge observed in human tissues potentially contains a veritable gold mine of information, which may be critical for the advancement of drug discovery.