Meal-induced Thermogenesis Research Articles

Exploring the physiological factors relating to energy balance in women with polycystic ovary syndrome: a scoping review.

Polycystic ovary syndrome (PCOS) occurs in 8%-13% of reproductive-aged women and is associated with reproductive, metabolic, and psychological dysfunction. Overweight and obesity are prevalent and exacerbate the features of PCOS. The aim of this review is to evaluate the extent of evidence examining the physiological factors affecting energy homeostasis, which may impact weight gain, weight loss, and weight maintenance in PCOS, and identify research gaps and recommendations for future research. Literature searches using MEDLINE, EMBASE, PsycInfo, AMED, CINAHL, and Cochrane Central Register of Controlled Trials were conducted up to June 22, 2022. Abstracts, non-English-language articles, and reviews were excluded. A total of n = 78 (n = 55 energy intake and n = 23 energy expenditure) primary research papers were included. Papers with multiple outcomes of interest were counted as separate studies. Energy-intake studies (n = 89) focussed on assessing food, nutrient, or supplements stimuli and were grouped into the outcomes of gastrointestinal appetite hormones (n = 43), adipokines (n = 34), subjective appetite (n = 9), functional brain imaging (n = 3), and neuropeptides (n = 0). Energy-expenditure studies (n = 29) were grouped into total energy expenditure (n = 1), resting energy expenditure (n = 15), meal-induced thermogenesis (n = 3), nutrient oxidation (n = 5), and metabolic flexibility (n = 5). Across both energy-intake and -expenditure papers, 60% of the studies compared outcome responses in women with PCOS with a control group. Results were inconsistent, with 57% reporting no differences and 43% reporting altered responses in PCOS compared with controls, including blunted appetite hormone responses, metabolic inflexibility, and reduced energy expenditure. The authors identified that there is inconsistent, yet preliminary, evidence of possible altered physiological factors, which may impact energy balance and weight management. Further work is needed to act on the identified clinical and research gaps to support women with PCOS and health professionals in informing and achieving realistic weight-management goals for women with PCOS. Systematic Review Registration: The protocol was prospectively registered on the Open Science Framework on February 16, 2021 (https://osf.io/9jnsm).

Adults with metabolically healthy overweight or obesity present more brown adipose tissue and higher thermogenesis than their metabolically unhealthy counterparts

There is a subset of individuals with overweight/obesity characterized by a lower risk of cardiometabolic complications, the so-called metabolically healthy overweight/obesity (MHOO) phenotype. Despite the relatively higher levels of subcutaneous adipose tissue and lower visceral adipose tissue observed in individuals with MHOO than individuals with metabolically unhealthy overweight/obesity (MUOO), little is known about the differences in brown adipose tissue (BAT). This study included 53 young adults (28 women) with a body mass index (BMI) ≥25kg/m2 which were classified as MHOO (n=34) or MUOO (n=19). BAT was assessed through a static 18F-FDG positron emission tomography/computed tomography scan after a 2-h personalized cooling protocol. Energy expenditure, skin temperature, and thermal perception were assessed during a standardized mixed meal test (3.5h) and a 1-h personalized cold exposure. Body composition was assessed by dual-energy x-ray absorptiometry, energy intake was determined during an ad libitum meal test and dietary recalls, and physical activity levels were determined by a wrist-worn accelerometer. Participants with MHOO presented higher BAT volume (+124%, P=0.008), SUVmean (+63%, P=0.001), and SUVpeak (+133%, P=0.003) than MUOO, despite having similar BAT mean radiodensity (P=0.354). In addition, individuals with MHOO exhibited marginally higher meal-induced thermogenesis (P=0.096) and cold-induced thermogenesis (+158%, P=0.050). Moreover, MHOO participants showed higher supraclavicular skin temperature than MUOO during the first hour of the postprandial period and during the cold exposure, while no statistically significant differences were observed in other skin temperature parameters. We observed no statistically significant differences between MHOO and MUOO in thermal perception, body composition, outdoor ambient temperature exposure, resting metabolic rate, energy intake, or physical activity levels. Adults with MHOO present higher BAT volume and activity than MUOO. The higher meal- and cold-induced thermogenesis and cold-induced supraclavicular skin temperature are compatible with a higher BAT activity. Overall, these results suggest that BAT presence and activity might be linked to a healthier phenotype in young adults with overweight or obesity. See acknowledgments section.

Secretin: An Old Hormone with a Burning Secret

Most theories of meal-induced thermogenesis involve a gut-brain-brown adipose tissue axis driving sympathetic nervous system-mediated thermogenesis. Li etal. demonstrate that secretin released by the gut after a meal binds to abundant receptors in brown adipose tissue to stimulate thermogenesis, inhibiting food intake and thereby suggesting a novel role for secretin regulating satiety.

Effect of macronutrient composition on meal-induced thermogenesis in adolescents with obesity.

Manipulation of meal macronutrient may be a useful way to modulate meal-induced thermogenesis (MIT) to induce increases in energy expenditure. The objective of this study was to examine in adolescents with obesity and of healthy weight and the effect of a high protein and high carbohydrate meal on MIT. An acute cross-over study with adolescents aged 11-19years was undertaken. Participants consumed in random order, a high 79% carbohydrate (HCHO), and a high 55% protein (HP) meal (adjusted to 25% of energy requirements). MIT and subjective appetite were assessed for 4h postprandial and an ad libitum lunch served. Data calculated as total AUC and expressed as mean ± SEM. Thirteen adolescents with obesity (mean BMI z score 2.3 ± 0.1) and 13 healthy weight (BMI z score 0.0 ± 0.2) participated. Mean MIT (% of energy intake) was greater after the HP (8.19 ± 0.709%) compared with the HCHO meal (4.36 ± 0.480%) (p < 0.001). The HP compared with the HCHO meal promoted greater fullness (12,994 ± 1208 vs 11,186 ± 1220mm/4h) (p = 0.016) and decreased hunger (8868 ± 1315 vs 10984mm ± 1438mm/4h) (p = 0.007). These effects observed were independent of body weight. High protein meals can increase MIT and fullness and reduce hunger compared with high carbohydrate meals in adolescents with obesity. Future research is warranted to determine if MIT can be targeted through manipulation of dietary choices to support weight management strategies. This study is registered with the Australian New Zealand Clinical Trials Registry (ANZCTR). Trial ID: ACTRN12612001066875.

No effect of saturated fatty acid chain length on meal-induced thermogenesis in overweight men

Monounsaturated (MUFA) fatty acids have been shown to induce greater meal-induced thermogenesis (MIT) than saturated fatty acids (SFA) in some studies, however, the effect of SFA chain length has not been examined. We hypothesized that a meal rich in short- to medium-chain SFA would elicit a greater MIT than one rich in long-chain SFA, and that MIT responses would be comparable between the short- to medium-chain SFA and the MUFA rich meal. A 3-arm crossover study was conducted with healthy overweight men, aged 18 to 40 years. Participants consumed either an iso-energetic (3780 ± 4.3 kJ), high fat (45%) meal rich in short-/medium-chain SFA (SMCSFA) (2-12 carbons); long-chain SFA (LCSFA) (14-24 carbons), and MUFA. MIT, fat oxidation, triglyceride and subjective appetite were measured for 6 hours post-prandial. Data were analyzed as total area under the curve and compared using a one-way repeated-measures ANOVA. The mean BMI of participants (n =13) was 29.3 ± 0.6 kg/m2 and mean age 23.8±1.4 years. MIT was not different between the meals: MUFA (204.2 ± 20.5 kJ/6 h), SMCSFA (192.6 ± 21.8 kJ/6 h), LCSFA (198.1 ± 21.5 kJ/6 h) (P = .888). Fat oxidation, plasma triglyceride, and hunger and fullness were similar after each meal (P > .05 all values). This study demonstrated that in healthy overweight men, SFA chain length, and fatty acid saturation have no acute differential effect on MIT, fat oxidation, triglyceride, or subjective appetite responses.

Whole-grain pasta reduces appetite and meal-induced thermogenesis acutely: a pilot study

In epidemiological studies, the intake of foods rich in dietary fiber is associated with a reduced risk of developing overweight and type 2 diabetes. This work aims to identify acute strategies to regulate appetite and improve glucose control by using different pasta meals. Hence, 4 different isocaloric lunch meals, consisting of (i) refined-grain pasta (RG+T), (ii) whole-grain pasta (WG+T), (iii) lemon juice-supplemented refined-grain pasta (LRG+T), and (iv) refined-grain pasta with legumes (RG+L), were administered to 8 healthy participants in a crossover design. On the test days, participants underwent baseline measurements, including appetite sensation, blood sample, and resting energy expenditure (EE), after which the test lunch was served. Subjective appetite was assessed and a blood sample was taken each hour for 240 min, and postprandial EE was measured for 3 h. In repeated-measures analysis of covariance (ANCOVA), postprandial fullness (p = 0.001) increased and hunger (p = 0.038) decreased. WG+T had a lower EE than did both LGR+T (p = 0.02) and RG+L (p < 0.001). Likewise, meal-induced thermogenesis was lower for WG+T compared with RG+L (58 ± 81 kJ vs 248 ± 188 kJ; p < 0.05). Plasma glucose (p = 0.001) was lower for RG+T, and triacylglycerols (p = 0.02) increased for LRG+T; however, insulin, C-peptide, and ghrelin were comparable in all other meals. In conclusion, our study indicates that acute consumption of whole-grain pasta may promote fullness and reduce hunger, lowering postprandial thermogenesis, and adding lemon juice to the pasta or legumes does not appear to affect appetite. However, none of pasta meal alterations improved the postprandial metabolic profile.

Reduced Insulin Sensitivity in Adults With Pseudohypoparathyroidism Type 1a

Disruption of the Gsα maternal allele leads to severe obesity and insulin resistance in mice and early-onset obesity in patients with pseudohypoparathyroidism (PHP) type 1a. However, insulin resistance and glucose metabolism have not been systematically characterized in patients with PHP1a. In a cross-sectional, case-control study, we examined insulin sensitivity, β-cell function, energy expenditure (EE), and sympathetic nervous system activity in adults with PHP1a. PHP1a patients (n = 8) and healthy control subjects (n = 24) matched for age (41 ± 7 vs 41 ± 7 years [mean ± SD]), gender, and percent body fat. Insulin sensitivity (SI), acute insulin response to glucose, and disposition index were assessed during a frequently sampled iv glucose tolerance test. Oral glucose insulin sensitivity (OGIS) was measured during a mixed meal. EE was measured using whole-room indirect calorimetry. Body composition was assessed via dual-energy x-ray absorptiometry and sympathetic nervous system activity by measuring 24-hour urinary catecholamine concentrations. PHP1a patients were less insulin-sensitive than their matched controls based upon SI and OGIS. Nondiabetic PHP1a patients tended to have a lower SI (P = .09) and reduced OGIS (P = .03). Disposition index, a composite measure of β-cell function, also tended to be lower in patients (P = .07). Total caloric intake, resting EE, total EE, meal-induced thermogenesis, and 24-hour urinary catecholamine concentrations were not significantly different between the groups. Adults with PHP-1a have reduced insulin sensitivity compared with their matched controls that may contribute to the pathogenesis of glucose intolerance and diabetes in these patients.

Metabolic Responses During Postprandial Exercise

To examine metabolic interaction between meal and exercise, 10 men and 10 women completed three trials: (1) exercise (E), (2) consumption of a meal (M), and (3) consumption of a meal followed by exercise (M+E). All trials commenced after an overnight fast and were preceded by a rest period in which resting metabolic rate (RMR) was determined. The meal contained 721 kilocalories composed of 41%, 36%, and 23% of carbohydrate, lipids, and protein, respectively. Exercise protocol consisted of three continuous 10-minute cycling at 50%, 60%, and 70% VO2peak. Measurement began 60 min after the start of the meal and included VO2 that was used to determine meal-induced thermogenesis (MIT). VO2 was greater (p < .05) in M+E than in E at 50% and 60% VO2peak. MIT was higher (p < .05) during exercise at 50% VO2peak than at rest. It appears that postprandial exercise of mild intensities can potentiate MIT, thereby provoking a greater increase in energy expenditure.

Methodological considerations for meal-induced thermogenesis: measurement duration and reproducibility

Meal-induced thermogenesis (MIT) research findings have been highly inconsistent, in part, due to the variety of durations and protocols used to measure MIT. In the present study, we aimed to determine the following: (1) the proportion of a 6h MIT response completed at 3, 4 and 5h; (2) the associations between the shorter durations and the 6h measures; (3) whether shorter durations improved the reproducibility of the measurement. MIT was measured in response to a 2410kJ mixed composition meal in ten individuals (five males and five females) on two occasions. Energy expenditure was measured continuously for 6h post-meal using indirect calorimetry, and MIT was calculated as the increase in energy expenditure above the pre-meal RMR. On average, 76, 89 and 96% of the 6h MIT response was completed within 3, 4 and 5h, respectively, and MIT at each of these time points was strongly correlated with the 6h MIT response (range for correlations, r 0·990-0·998; P<0·01). The between-day CV for the 6h measurement was 33%, but it was significantly lower after 3h of measurement (CV 26%; P=0·02). Despite variability in the total MIT between days, the proportion of MIT that was completed at 3, 4 and 5h was reproducible (mean CV: 5%). While 6h are typically required to measure the complete MIT response, the 3h measures provide sufficient information about the magnitude of the MIT response and may be applicable for testing individuals on repeated occasions.

Leucine balance, metabolic and satiety responses to a leucinerich meal in healthy elderly women

Many older adults experience a decline of appetite and may not meet their protein needs; a strategy to optimize protein retention is thus essential. Leucine has anabolic potential by stimulating protein synthesis via mRNA translation and insulin secretion. Postprandial responses to leucine‐rich versus isonitrogenous mixed meals were assessed in 9 healthy older women (70.1±2 y, BMI 23.7±2.7 kg/m2) by double‐blinded, randomized, crossover studies. Test meals provided 0.6 g protein and 16.0 kcal/kg LBM, once with added leucine (0.07 g/kg LBM), once without.ResultsFive‐hour whole‐body postprandial leucine oxidation response, measured by constant infusion of [1‐13C]leucine and enrichment of plasma 13C‐KIC and expired 13CO2 was further increased with meal+leucine. Yet, the resulting balance (intake‐oxidation) was greater (18.1±1.4 vs. without 11.3±1.3 mmol/5h, p&lt;0.001) suggesting more protein retention. Serum insulin and C‐peptide AUC were greater post meal+leucine, indicating more secretion. Plasma glucose excursions and free fatty acids suppression did not differ between meals. Addition of leucine had no effect on meal‐induced thermogenesis, satiety and gut peptide responses (GLP‐1, PYY 3–36, ghrelin). This study shows the anabolic potential of a leucine‐rich mixed meal in older women, a dietary strategy that may be used to promote protein anabolism without affecting appetite. (Funded by CIHR)

Effect of Honey versus Sucrose on Appetite, Appetite-Regulating Hormones, and Postmeal Thermogenesis

Objective: Increased per capita consumption of sweeteners may be responsible in part for the rising prevalence of obesity in the United States. Recent studies suggest that consumption of honey is not associated with this same obesogenic effect and may have beneficial effects neuro on body weight. The purpose of this study was to evaluate whether the meal-induced responses of ghrelin and peptide YY3-36 (PYY3-36) and/or meal-induced thermogenesis differ following a honey- versus a sucrose-containing meal.Methods: In a double-blind randomly assigned study, appetite hormones (ghrelin, PYY3-36, leptin) and glycemic and thermic responses were evaluated following isoglucidic ∼450 kcal honey- or sucrose-containing breakfasts in 14 healthy, nonobese women (22 ± 3 y). Blood samples and hunger ratings were obtained at baseline and every 30 minutes for 240 minutes following the meal. Meal-induced thermogenesis was measured by indirect calorimetry. Ad libitum food intake was evaluated from a free-choice meal following the test meal.Results: Honey consumption delayed the postprandial ghrelin response (p = 0.037), enhanced the total PYY (p = 0.007) response, and blunted the glucose response (p = 0.039) compared with consumption of the sucrose-containing meal. Meal-induced insulin response, hunger ratings, thermogenesis, and subsequent ad libitum food intake, however, did not differ (p > 0.10) between diet treatments.Conclusions: Alterations in meal-induced responses of ghrelin and PYY3-36 but not meal-induced thermogenesis may be responsible in part for the potential “obesity protective” effect(s) of honey consumption. A blunted glycemic response may be beneficial for reducing glucose intolerance. Further research is required to determine if these findings hold true for obese individuals, for males, or with habitual consumption.

Meal-induced thermogenesis and macronutrient oxidation in lean and obese women after consumption of carbohydrate-rich and fat-rich meals

Objective To examine differences in meal-induced thermogenesis and macronutrient oxidation between lean and obese women after consumption of two different isocaloric meals, one rich in carbohydrate (CHO) and one rich in fat. Methods A total of 19 lean and 22 obese women were studied on two occasions, 1 wk apart. In one visit they consumed a CHO-rich meal and in the other visit a fat-rich meal. The two meals were isocaloric and were given in random order. Resting energy expenditure and macronutrient oxidation rates were measured and calculated in the fasting state and every hour for 3 h after meal consumption. Results Meal-induced thermogenesis was not different between lean and obese subjects after the CHO-rich ( P = 0.89) or fat-rich ( P = 0.32) meal, but it was significantly higher after the CHO-rich compared with the fat-rich meal in the lean and the obese individuals ( P < 0.05). Protein oxidation rate increased slightly but significantly after the test meals in both groups ( P < 0.01). Fat oxidation rate decreased after consumption of the CHO-rich meal ( P < 0.001), whereas it increased after consumption of the fat-rich meal in both groups ( P < 0.01). CHO oxidation rate increased in both groups after consumption of the CHO-rich meal ( P < 0.001). Oxidation rates of protein, fat, and CHO during the experiment were not significantly different between lean and obese participants. Conclusion Meal-induced thermogenesis and macronutrient oxidation rates were not significantly different between lean and obese women after consumption of a CHO-rich or a fat-rich meal.

Simple Exercise Recovery Index for Sympathetic Overactivity Is Linked to Insulin Resistance

Exercise HR recovery (HRR) has proven an effective clinical means to assess parasympathetic dysfunction linked to all-cause mortality, but an analogous functional assessment for sympathetic dysfunction has not been developed. We investigated whether exercise recovery provides additional cardiorespiratory information, beyond the initial HRR period, to index sympathetic overactivity associated with insulin resistance. Young people (N = 20) with diverse percent body fat (9%-52%) were studied using fasting, oral glucose tolerance test (OGTT), and high-carbohydrate meal measurements. Participants also completed a graded fitness test (oxygen consumption peak test on cycle ergometer) after which HR and oxygen consumption (V x O2) measurements were continued for 3 min into recovery. The first, rapid phase of exercise recovery was used as the clinical measurement for parasympathetic control (HRR = HR2 min - HRmax). The second, initial plateau phase of exercise recovery was used to calculate a novel functional index for sympathetic overactivity (the plateau value for the ratio of HR normalized for V x O2 (HR/V x O2 plat)). As expected, parasympathetic function (HRR) was within the normal range in these young people (-58 +/- 2 bpm). The index for sympathetic overactivity varied over a wide range from 9 to 34 bpm/(mL x kg x min(-1)), with obese adolescents having values in the highest 25th percentile. We found that this simple index was correlated to both the OGTT-derived whole-body insulin sensitivity index (r = -0.74, P < 0.001) and Homeostasis Assessment Model for Insulin Resistance (r = 0.76, P < 0.001), independent of percent body fat and parasympathetic function. Meal-induced thermogenesis was also associated with HR/V x O2 plat (r = -0.64, P < 0.01) but not with HRR. In young individuals, recovery from intense exercise may provide a simple means to quantify both parasympathetic and sympathetic function. The exercise recovery index for sympathetic overactivity was linked to insulin resistance.

Effect on 24-h energy expenditure of a moderate-fat diet high in monounsaturated fatty acids compared with that of a low-fat, carbohydrate-rich diet: a 6-mo controlled dietary intervention trial

Background:Dietary fat has a lower thermogenic effect than does carbohydrate. A moderate-fat diet, high in monounsaturated fatty acids (MUFA diet), may decrease energy expenditure (EE) and thereby induce weight gain.Objective:We aimed to compare changes in 24-h EE and substrate oxidation after a 6-mo controlled dietary intervention with either a MUFA or a low-fat (LF) diet.Design:Twenty-seven overweight [body mass index (in kg/m2): 28.1 ± 0.4] nondiabetic subjects aged 18–36 y followed an 8-wk low-calorie diet and a 2-wk weight-stabilizing diet and then were randomly assigned to a MUFA (n= 12) or LF (n= 15) diet for 6 mo. Substrate oxidation and 24-h EE were measured by whole-body indirect calorimetry. The first measurement (0 mo) was taken during the weight-stabilizing diet, and the second measurement was taken after the 6-mo intervention.Results:A tendency was seen toward a lower 24-h EE with the MUFA than with the LF diet (P= 0.0675), but this trend did not remain after adjustment for the initial loses of fat mass and fat-free mass (P= 0.2963). Meal-induced thermogenesis was significantly (P< 0.05) lower with the MUFA than with the LF diet, but no time × treatment interaction was found. A significant (P= 0.0456) treatment × time interaction was found for spontaneous physical activity.Conclusion:Despite a slightly lower meal-induced thermogenesis, the MUFA diet had an effect on 24-h EE that was not significantly different from that of the LF diet after a 6-mo controlled dietary intervention.

Differential effects of high-fat and high-carbohydrate isoenergetic meals on cardiac autonomic nervous system activity in lean and obese women

Food ingestion can influence autonomic nervous system activity. This study compares the effects of 2 different isoenergetic meals on sympathetic nervous system (SNS) activity, assessed by heart rate variability (HRV) and plasma norepinephrine (NE) levels, in lean and obese women. Fifteen lean and 15 obese healthy women were examined on 2 occasions: after a carbohydrate (CHO)-rich and after a fat-rich test meal. Measurements of blood pressure, heart rate, resting energy expenditure, plasma glucose, lipids, insulin, leptin, and NE, as well as spectral analysis of the HRV, were performed at baseline and every 1 hour for 3 hours after meals. At baseline, obese women had higher SNS activity than lean controls (higher values of low-to-high frequency ratio [LF/HF], 1.52 ± 0.31 v 0.78 ± 0.13, P = .04; and plasma NE levels, 405.6 ± 197.9 v 240.5 ± 95.8 pg/mL, P < .0001). After the CHO-rich meal a greater increase in LF/HF and in plasma NE levels was observed in lean, compared to obese women (1.21 ± 0.6 v 0.32 ± 0.06, P = .04; and 102.9 ± 35.4 v 38.7 ± 12.3 pg/mL, P = .01, respectively), while no differences were observed after the fat-rich meal. Meal-induced thermogenesis was higher after the CHO-rich as compared to the fat-rich meal and was comparable between lean and obese women. Changes in HRV were not associated with the thermogenic response to the test meals. In conclusion, consumption of a CHO-rich meal causes greater cardiac SNS activation in lean than in obese women, while fat ingestion does not result in any appreciable change in either group. SNS activation does not appear to influence the thermic effect of the food in either lean or obese women.

Invited review: Aging and energy balance.

Humans over 70 yr of age often lose weight. This appears to be due to a physiological anorexia of aging as well as a loss of lean mass (sarcopenia) and, to a lesser extent, fat mass. The causes of the physiological anorexia of aging include changes in taste and smell and a decrease in adaptive relaxation of the fundus of the stomach, which leads to more rapid antral filling and early satiation. In addition, basal and stimulated levels of the satiating hormone, cholecystokinin, are increased. In men, the decline in testosterone leads to an increase in leptin and a loss of lean mass. Although resting metabolic rate declines with aging, this is mainly due to the decline in lean body mass. Energy metabolism is also decreased due to a decline in Na+-K+-ATPase activity, decreased muscle protein turnover, and possibly changes in mitochondrial membrane protein permeability. Physical energy expenditure declines with aging. Meal-induced thermogenesis shows a delay to peak, possibly due to a delay in gastric emptying. Inadequate data are available on the effect of aging in humans on other energy-producing mechanisms such as adaptive thermogenesis. These physiological changes place older men and women at major risk of developing pathological weight loss when they develop disease states, especially those associated with cytokine elaboration.

Energy restriction with protein restriction increases basal metabolism and meal-induced thermogenesis in rats.

We previously observed an increased sympathetic nervous system (SNS) activity that was partly responsible for a defect in the insulin secretion response to glucose after postweaning protein-energy restriction (PER) in female rats. These results, together with other data on low-protein feeding, suggested that a low protein-to-energy ratio (P/E) in the diet could stimulate energy expenditure (EE), but direct measurements of EE have never been reported under conditions of PER. The goal of the present study was thus to quantify the changes induced by PER to body composition, the various parameters of EE, and plasma triiodothyronine levels. PER induced severe growth retardation, but the subcutaneous white and interscapular brown adipose tissue masses were preserved. Basal metabolism, meal-induced thermogenesis, and triiodothyronine levels were increased, but substrate utilization by the working muscles was unaffected. Meal-induced thermogenesis was increased by spontaneous activity in PER rats only. These results suggest that rats adapt to a low P/E in the diet by burning part of their excess nonprotein energy and storing the remaining excess in subcutaneous adipose tissue.

Obesity in children and adolescents worldwide: current views and future directions--Working Group Report of the First World Congress of Pediatric Gastroenterology, Hepatology, and Nutrition.

Obesity in children and adolescents worldwide: current views and future directions--Working Group Report of the First World Congress of Pediatric Gastroenterology, Hepatology, and Nutrition.

Adrenalectomy abolishes the food-induced hypothalamic serotonin release in both normal and monosodium glutamate-obese rats

Corticosteroids influence energy homeostasis through centrally-mediated stimulation of energy intake and inhibition of expenditure, while central serotonin (5-HT) has opposite effects. Both serotonergic dysfunction and high glucocorticoid levels may be relevant in obesity. The neurotoxin monosodium glutamate (MSG) induces a non-hyperphagic and hypometabolic obesity with hypercorticosteronemia. We investigated the influence of corticosterone levels on the serotonergic system of MSG-obese and control rats. Applying microdialysis, we found a similar feeding-induced stimulation of serotonin release in the lateral hypothalamus (LH) in sham-adrenalectomized control and MSG rats. The concomitant serum corticosterone variations were markedly distinct between them, in that an increase occurred in the control group, while the initially high levels of the MSG rats decreased with feeding. It is suggested that this lowering of corticosterone prevented a higher serotonergic activation, which would lead to a higher meal-induced thermogenesis and a better adequation of the caloric intake to a low metabolism. Adrenalectomy completely abolished the feeding-evoked serotonergic stimulation in both groups. This observation demonstrates that glucocorticoids are necessary for food intake to acutely stimulate 5-HT release and indicates that serotonergic activity in the LH is not likely to participate in the adrenalectomy-induced attenuation of the MSG-obesity.

Postprandial Thermogenesis Is Increased 100% on a High-Protein, Low-Fat Diet versus a High-Carbohydrate, Low-Fat Diet in Healthy, Young Women

Objective: The recent literature suggests that high-protein, low-fat diets promote a greater degree of weight loss compared to high-carbohydrate, low-fat diets, but the mechanism of this enhanced weight loss is unclear. This study compared the acute, energy-cost of meal-induced thermogenesis on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet.Methods: Ten healthy, normal weight, non-smoking female volunteers aged 19-22 years were recruited from a campus population. Using a randomized, cross-over design, subjects consumed the high-protein and the high-carbohydrate diets for one day each, and testing was separated by a 28- or 56-day interval. Control diets were consumed for two days prior to each test day. On test day, the resting energy expenditure, the non-protein respiratory quotient and body temperature were measured following a 10-hour fast and at 2.5-hour post breakfast, lunch and dinner. Fasting blood samples were collected test day and the next morning, and complete 24-hour urine samples were collected the day of testing.Results: Postprandial thermogenesis at 2.5 hours post-meal averaged about twofold higher on the high protein diet versus the high carbohydrate diet, and differences were significant after the breakfast and the dinner meals (p < 0.05). Body temperature was slightly higher on the high protein diet (p = 0.08 after the dinner meal). Changes in the respiratory quotient post-meals did not differ by diet, and there was no difference in 24-hour glomerular filtration rates by diet. Nitrogen balance was significantly greater on the high-protein diet compared to the high-carbohydrate diet (7.6 ± 0.9 and −0.4 ± 0.5 gN/day, p < 0.05), and at 24-hour post-intervention, fasting plasma urea nitrogen concentrations were raised on the high protein diet versus the high-carbohydrate diet (13.9 ± 0.9 and 11.2 ± 1.0 mg/dL respectively, p < 0.05).Conclusions: These data indicate an added energy-cost associated with high-protein, low-fat diets and may help explain the efficacy of such diets for weight loss.