Fasting glucagon-like peptide 1 concentration is associated with lower carbohydrate intake and increases with overeating.

PURPOSE: Glucagon-like peptide 1 (GLP-1) is an incretin hormone that appears to play a major role in the control of food intake. The aim of this investigation was to evaluate and quantify the association of circulating GLP-1 concentration with ad libitum total calorie and macronutrient intake. METHODS: One-hundred and fifteen individuals (72 men) aged 35 ± 10 years were admitted for an inpatient study investigating the determinants of energy intake. Ad libitum food intake was assessed during 3 days using a reproducible vending machine paradigm. Fasting plasma GLP-1 concentrations were measured on the morning of the first day and on the morning of the fourth day after ad libitum feeding. RESULTS: Plasma GLP-1 concentrations increased by 14% after 3 days of ad libitum food intake. Individuals overate on average 139 ± 45% of weight-maintaining energy needs. Fasting plasma GLP-1 on day 1 was negatively associated with carbohydrate intake (r = - 0.2, p = 0.03) and with daily energy intake from low fat-high simple sugar (r = - 0.22, p = 0.016). CONCLUSION: Higher plasma GLP-1 concentrations prior to ad libitum food intake were associated with lower carbohydrate intake and lower simple sugar ingestion, indicating a possible role of the GLP-1 in the reward pathway regulating simple sugar intake. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00342732.

Lower core body temperature and greater body fat are components of a human thrifty phenotype.

BACKGROUND/OBJECTIVES: In small studies, a thrifty human phenotype, defined by a greater 24-hour energy expenditure (EE) decrease with fasting, is associated with less weight loss during caloric restriction. In rodents, models of diet-induced obesity often have a phenotype including a reduced EE and decreased core body temperature. We assessed whether a thrifty human phenotype associates with differences in core body temperature or body composition. SUBJECTS/METHODS: Data for this cross-sectional analysis were obtained from 77 individuals participating in one of two normal physiology studies while housed on our clinical research unit. Twenty-four-hour EE using a whole-room indirect calorimeter and 24-h core body temperature were measured during 24 h each of fasting and 200% overfeeding with a diet consisting of 50% carbohydrates, 20% protein and 30% fat. Body composition was measured by dual X-ray absorptiometry. To account for the effects of body size on EE, changes in EE were expressed as a percentage change from 24-hour EE (%EE) during energy balance. RESULTS: A greater %EE decrease with fasting correlated with a smaller %EE increase with overfeeding (r=0.27, P=0.02). The %EE decrease with fasting was associated with both fat mass and abdominal fat mass, even after accounting for covariates (ß=-0.16 (95% CI: -0.26, -0.06) %EE per kg fat mass, P=0.003; ß=-0.0004 (-0.0007, -0.00004) %EE kg(-1) abdominal fat mass, P=0.03). In men, a greater %EE decrease in response to fasting was associated with a lower 24- h core body temperature, even after adjusting for covariates (ß=1.43 (0.72, 2.15) %EE per 0.1 °C, P=0.0003). CONCLUSIONS: Thrifty individuals, as defined by a larger EE decrease with fasting, were more likely to have greater overall and abdominal adiposity as well as lower core body temperature consistent with a more efficient metabolism.

Body composition and energy expenditure predict ad-libitum food and macronutrient intake in humans.

BACKGROUND: Obesity is the result of chronic positive energy balance. The mechanisms underlying the regulation of energy homeostasis and food intake are not understood. Despite large increases in fat mass (FM), recent evidence indicates that fat-free mass (FFM) rather than FM is positively associated with intake in humans. METHODS: In 184 humans (73 females/111 males; age 34.5±8.8 years; percentage body fat: 31.6±8.1%), we investigated the relationship of FFM index (FFMI, kg m(-2)), FM index (FMI, kg m(-2)); and 24-h energy expenditure (EE, n=127) with ad-libitum food intake using a 3-day vending machine paradigm. Mean daily calories (CAL) and macronutrient intake (PRO, CHO, FAT) were determined and used to calculate the relative caloric contribution of each (%PRO, %CHO, %FAT) and percent of caloric intake over weight maintaining energy needs (%WMENs). RESULTS: FFMI was positively associated with CAL (P<0.0001), PRO (P=0.0001), CHO (P=0.0075) and FAT (P<0.0001). This remained significant after adjusting for FMI. Total EE predicted CAL and macronutrient intake (all P<0.0001). FMI was positively associated with CAL (P=0.019), PRO (P=0.025) and FAT (P=0.0008). In models with both FFMI and FMI, FMI was negatively associated with CAL (P=0.019) and PRO (P=0.033). Both FFMI and FMI were negatively associated with %CHO and positively associated with %FAT (all P<0.001). EE and FFMI (adjusted for FMI) were positively (EE P=0.0085; FFMI P=0.0018) and FMI negatively (P=0.0018; adjusted for FFMI) associated with %WMEN. CONCLUSION: Food and macronutrient intake are predicted by FFMI and to a lesser degree by FMI. FFM and FM may have opposing effects on energy homeostasis.

Sustained increase in dietary oleic acid oxidation following morning exercise.

OBJECTIVE: We have previously reported that prior exercise increases the oxidation of dietary monounsaturated fat in comparison to rest when the fat is given in a mixed meal 30 min following the completion of exercise. In this study, we determined whether the increase in dietary fat oxidation after exercise persisted when the time between exercise and fatty acid administration was lengthened. DESIGN: Six female subjects (age=24+/-0.1 y, BMI=21+/-1 kg/m2) were recruited for a total of six visits each. During three visits, a stationary cycle exercise session (1250 kJ) was performed at 65% VO2 peak in a whole-body calorimeter; while during three other visits, exercise was replaced with rest. Subjects received [1-13C]oleate and [d31]palmitate with a different meal at each visit: breakfast, lunch, and dinner. RESULTS: Dietary oleate oxidation following prior rest did not differ between dose times and was 36+/-3, 42+/-5, and 42+/-3% for the 13 h following breakfast, lunch, and dinner. Prior exercise resulted in greater oleate oxidation following all dose times than prior rest (P<0.01) being 52+/-4, 64+/-3, and 53+/-3% for the breakfast, lunch, and dinner dose. The oxidation was significantly greater following lunch than the other dose times (P<0.05). Prior exercise (1250 kJ) did not result in greater oxidation of palmitate; however, oxidation following prior exercise increased with later dose times (13+/-2, 23+/-2, and 23+/-3% for breakfast, lunch, and dinner; P<0.05) and following rest (18+/-2, 22+/-2, and 27+/-2% for breakfast, lunch, and dinner; P<0.005). CONCLUSIONS: The increase in oleate oxidation when administered after early morning exercise was found to persist for all three meals of the day, with the greatest effect occurring for the lunch meal. Palmitate oxidation, while apparently resistant to the effects of 1250 kJ of prior exercise, increases when administered later in the day, suggesting a diurnal variation in the oxidation of dietary fatty acids. These results demonstrate that prior exercise selectively alters the partitioning of dietary fatty acids. Furthermore, these findings demonstrate additional benefits of substituting monounsaturated for saturated fatty acids in the diet.

Pattern and cost of weight gain in previously obese women.

Weight gain is common among postobese individuals, providing an opportunity to address the cost of weight regain on energy expenditure. We investigated the energy cost of weight regain over 1 yr in 28 women [age 39.5 +/- 1.3 (SE) yr; body mass index 24.2 +/- 0.5 kg/m(2)] with recent weight loss (>12 kg). Body composition, total energy expenditure (TEE) using doubly labeled water, resting metabolic rate (RMR), and thermic effect of a meal (TEM) were assessed at 0 and 12 mo. Metabolizable energy intake (MEI) was calculated from TEE and change in body composition. Fourteen women had a weight gain of 13.2 +/- 2.1 kg. Twelve-month cumulative excess MEI, calculated as the intake in excess of TEE at month 0, was 749 +/- 149 MJ. Of this, 462 +/- 83 MJ (62%) were stored as accrued tissue, and 287 +/- 72 MJ (38%) was increased TEE. Expressed per kilogram of body weight gain, the energy cost of weight gain was calculated to be 54.8 +/- 4.6 MJ/kg. Interestingly, weight regain time courses fell into three distinct patterns, possibly requiring varying countermeasures.

Validation of deuterium labeled fatty acids for the measurement of dietary fat oxidation: a method for measuring fat-oxidation in free-living subjects.

BACKGROUND: Fatty acid oxidation has frequently been measured using (13)C or (14)C labeled fatty acids. While providing valuable data, the breath test method is hindered by the need for a controlled environment to measure VCO(2) and collect frequent breath samples. Additionally, the CO(2) breath tests require the use of (13)C- or (14)C-acetate to correct for isotope exchange in the TCA cycle. We validated d(31)-palmitic acid for measuring dietary fat oxidation. When oxidized, the deuterium appears as water and mixes with the body water pool providing a cumulative record of fat oxidation. METHODS: The recovery of deuterium from d(31)-palmitic acid at 10 h post-dose was compared to that of (13)CO(2) from [1-(13)C]-palmitic acid in nine subjects (body mass index (BMI)=23.6+/-2.8; percentage body fat (%BF)=22.6+/-5.3; mean+/-s.d.). Subjects were studied at rest. [1-(13)C]-acetate (2 mg/kg) was dosed in a liquid breakfast. On a second day, [1-(13)C]-palmitic acid (10 mg/kg) and d(31)-palmitic acid (15 mg/kg) were dosed with the same liquid breakfast. RESULTS: Recovery of (13)CO(2) from [1-(13)C]-acetate at 10 h post-dose was 53.7+/-10.4%. Recovery of d(31)-palmitic acid was 13.2+/-7.7% (mean+/-s.d.) and [1-(13)C]-palmitic acid recovery was 6.4+/-3.6%. When the (13)C data was corrected for [1-(13)C]-acetate (Na salt) recovery, the mean difference in percentage recovery between the two tracers was 0.5+/-2.8% and cumulative recoveries through 10 h post-dose were highly correlated (y=1.045x - 0.47; r(2)=0.88, P<0.0002). Our data shows both labels to be equivalent in their ability to measure dietary fat oxidation in resting subjects. CONCLUSIONS: The use of deuterium labeled palmitic acid eliminates the need for rigid control over the subjects' environment. Frequent sampling and measurement of VCO(2) are not needed for accurate calculation of percentage recovery of the deuterium label. In addition, the deuterium label has a decreased potential for isotopic exchange compared to (13)C or (14)C, so a recovery correction factor is probably not required.

The role of exercise in the treatment of obesity.

The prevalence of obesity in the USA has increased dramatically in the past decade. This foreshadows an increase in the rates of morbidity and mortality from obesity-related diseases and increases in the number of individuals undergoing weight-loss therapy. Although exercise has long been recommended for inclusion in such therapy, the present review has found that it has had little or no effect on weight loss per se when the exercise is limited to the typically prescribed 3-5 h/wk of moderate or vigorous activity. However, further review has shown that exercise helps to preserve and at times even increase fat-free mass during weight loss. At the same time, fat loss is generally increased. Neither type nor amount of exercise appears to have much effect during treatment, with the possible exception of resistance training, which is associated with the best outcome for fat-free mass. The most important role of exercise, however, is in the maintenance of the weight loss. In this respect, the volume of exercise seems to be important because several lines of evidence have indicated that exercise must expend roughly 2500 kcal/wk to maintain weight loss. Studies of weight maintenance, however, have generally not included randomized controls; thus, further research is required to solidify these conclusions.