Reliability of the measurement of postprandial thermogenesis in men of three levels of body fatness.

To determine the reliability of the measurement of postprandial thermogenesis by indirect calorimetry and to clarify further the relationship of obesity to thermogenesis in men, the thermic effect of a 720-kcal, mixed liquid meal was compared in 13 lean men (mean +/- SEM, 11.2% +/- 1.4% body fat), 10 average men (22.4% +/- 1.6% body fat), and 12 obese men (33.4% +/- 1.6% body fat) on two occasions. Resting metabolic rate (RMR) was measured for 3 hours: (1) in the fasted state, and (2) after a 720-kcal mixed liquid meal, on two occasions. The thermic effect of the meal, calculated as the postprandial energy expenditure minus the fasting RMR (kcal/3h), was greater for the lean and average men than for the obese men during both trials (P less than .001), but was only marginally different between the lean and average groups (P = .16). The mean values for the two trials were similar and the measurement of thermogenesis was highly reproducible with a reliability coefficient of r = .932 (P less than .001). Across all groups, thermogenesis correlated strongly with percent body fat (r = -.64, P less than .01), but within the average men, thermogenesis was uncorrelated with percent body fat (r = .09) but highly correlated with the glucose response to the meal (r = -.75, P less than .05). Thus, factors other than body fatness, such as insulin sensitivity, may determine thermogenesis within this heterogeneous middle group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermic effect of a meal over 3 and 6 hours in lean and obese men

Controversy regarding defective postprandial thermogenesis in obesity may partly be due to methodological factors such as duration of measurement. To clarify further the role of blunted thermogenesis in obesity, the thermic effect of food was compared in seven lean (mean +/- SEM, 15.7% +/- 1.5% body fat, by densitometry) and seven obese men (37.3% +/- 3% fat) over 3 and 6 hours. The groups were matched for age (35 +/- 2 and 33 +/- 2 years for the lean and obese groups; range, 25 to 39 years), fat-free mass (FFM), and aerobic fitness. Resting metabolic rate (RMR) was measured by indirect calorimetry for 6 hours on two mornings, in randomized order: (1) after a 720-kcal liquid mixed meal, which was 24% protein, 21% fat, and 55% carbohydrate; and (2) in the postabsorptive state. The thermic effect of food, calculated as postprandial minus postabsorptive RMR, was significantly greater for the lean than obese men for the first 3 hours of measurement (67 +/- 6 v 49 +/- 3 kcal/3 hours; P less than .01). During the second 3 hours, the thermic effect of food was marginally, but not significantly, greater for the lean than obese men (34 +/- 8 v 20 +/- 4 kcal/3 hours; P = .10, NS). Over the entire 6 hours, the thermic effect of food was significantly greater for the lean than obese men (100 +/- 12 v 69 +/- 5 kcal/6 hours; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of diet on energy expenditure and plasma norepinephrine in lean and obese Pima Indians

To assess whether thermogenesis or sympathetic nervous system (SNS) function might differ between lean and obese human subjects, studies of thermic and sympathetic responses to standard stimuli were undertaken in Pima Indians, an ethnic group with a high prevalence of obesity. Plasma levels of norepinephrine (NE) and energy expenditure at rest and in response to feeding, exercise, and graded infusions of NE were compared in five lean and five obese Indians during a period of weight maintenance (WM), after 3 weeks of overfeeding (OF) and, in the obese, also after 6 weeks of underfeeding (UF). Basal energy expenditure, when adjusted for fat free mass, was equivalent during WM and increased 3% with OF (P less than 0.01) in both groups. Thermic responses to exercise or a test meal did not differ in lean and obese and did not change with OF, while thermic responses to NE infusion fell during OF to a greater degree in obese than lean (P less than 0.05). A similar pattern (decreased effect in obese with OF) was also noted in the glycemic response to infused NE (P less than 0.05). Although not quantitatively different in lean and obese, the plasma NE concentration appeared to vary more in response to feeding or dietary alteration in the obese than lean, a finding that may reflect lower plasma clearance of NE in the obese. These studies, therefore, raise the possibility that overfeeding in obese Pima Indians may limit the contribution of sympathetically mediated thermogenesis to energy expenditure, though the implications of this for body weight regulation are speculative.     

Resting metabolic rate and postprandial thermogenesis in polycystic ovarian syndrome

To determine whether the high frequency of obesity in women with polycystic ovary syndrome (PCO) is related to a defect in energy expenditure, resting metabolic rate (RMR) and the thermic response to a standard meal were compared in 10 obese PCO women, nine obese but otherwise normal women, and 11 lean women. All groups were matched with respect to age and fat-free mass and the two obese groups were matched for degree of obesity. RMR was measured by indirect calorimetry for 3 h on two days: (1) in the postabsorptive state; and (2) after a 720 kcal (3014 kJ) liquid mixed meal. The thermic effect of food, calculated as 3 h postprandial minus fasting RMR, was significantly greater for the lean [52.9 +/- 5.5 kcal/3 h (221 +/- 23 kJ/3 h)] than the obese [17.2 +/- 5.1 kcal/3 h (72 +/- 21 kJ/3 h)] and the PCO women [22.8 +/- 5.2 kcal/3 h (95 +/- 22 kJ/3)], P less than 0.001). The thermic effect of food was negatively related to percent body fat (r = -0.694, P less than 0.001). Resting metabolic rate did not differ significantly among the three groups, and was strongly related to fat-free mass (r = 0.687, P less than 0.001). These results confirm previous reports of blunted thermogenesis in obese individuals, but provide no evidence of altered resting metabolic rate or postprandial thermogenesis in women with PCO compared with normal women of similar degree of obesity.     

Thermic effect of food at rest and following swim exercise in trained college men and women

The calorigenic effect of a liquid meal was studied in 8 (5 male, 3 female) lean, trained swimmers to assess the effect of swim exercise on dietary-induced thermogenesis. Metabolic rate was measured by indirect calorimetry under 3 conditions: (A) 4 h postexercise in the postabsorptive state; (B) 4 h of rest in the postprandial state, and (C) 4 h postexercise in the postprandial state. At 20 min postexercise metabolic rate had increased 22% over RMR; however, by 40 min postexercise it had returned to the preexercise level. Following both conditions B and C oxygen consumption (VO2) remained significantly elevated for 3 h. The mean rise in caloric expenditure was 24.8 kcal/h when exercise preceded the meal, compared to 20.2 kcal/h when exercise was not performed. This difference of approximately 18 kcal/4 h, although of negligible importance in short-term energy balance, could be significant in long-term energy regulation, and thus contribute to body weight control.     

The effect of exercise training on beta-adrenergic stimulation of fat metabolism in obese men

OBJECTIVE: To investigate the in vivo effect of exercise training at high and low intensity on beta-adrenergic stimulated fat metabolism in obese men at rest. METHOD: Twenty-three obese, healthy subjects were randomly divided in a low-intensity exercise training program (40% VO(2max), n=7), a high-intensity exercise training program (70% VO(2max); n=8), or a non-exercising control group (n=8). The exercise training program lasted for 12 weeks with a training frequency of 3 times per week. Before and after the intervention body composition and maximal aerobic capacity were measured as well as fat metabolism at rest and during beta-adrenergic stimulation by isoprenaline. For comparison, six lean subjects served as a control group. They participated in a low-intensity exercise training program and underwent the same measurements as the obese subjects. RESULTS: Relative fat oxidation decreased significantly during infusion of an increasing dose of isoprenaline in the obese low-intensity and high-intensity exercise training groups as well as in the lean group (P<0.01). Exercise training failed to influence the effect of beta-adrenergic stimulation on relative fat oxidation in obese men at both intensities and in lean men. In addition, beta-adrenergic-mediated lipolysis did not seem to be different after low intensity exercise training in lean and obese men. Lipolysis might be increased after high-intensity exercise training in obese men. CONCLUSION: Low- and high-intensity exercise training in obese men failed to affect beta-adrenergic mediated relative fat oxidation in vivo. beta-Adrenergic-mediated lipolysis might be increased in obese men after HI exercise training only. The effect of low-intensity exercise training on beta-adrenergic-mediated fat metabolism was similar in lean and obese men. International Journal of Obesity (2001) 25, 16-23     

Meal-induced thermogenesis and obesity: is a fat meal a risk factor for fat gain in children?

Diet composition, in particular fat intake, has been suggested to be a risk factor for obesity in humans. Several mechanisms may contribute to explain the impact of fat intake on fat gain. One factor may be the low thermogenesis induced by a mixed meal rich in fat. In a group of 11 girls (10.1 +/- 0.3 yr), 6 obese (body mass index, 25.6 +/- 0.6 kg/m(2)), and 5 nonobese (body mass index, 19 +/- 1.6 kg/m(2)), we tested the hypothesis that a mixed meal rich in fat can elicit energy saving compared with an isocaloric and isoproteic meal rich in carbohydrate. The postabsorptive resting energy expenditure and the thermic effect of a meal (TEM) after a low fat (LF; 20% fat, 68% carbohydrate, and 12% protein) or an isocaloric (2500 kJ or 600 Cal) and isoproteic high fat (HF; 48% fat, 40% carbohydrate, and 12% protein) meal were measured by indirect calorimetry. Each girl repeated the test with a different, randomly assigned menu (HF or LF) 1 week after the first test. TEM, expressed as a percentage of energy intake was significantly higher after a LF meal than after a HF meal (6.5 +/- 0.7% vs. 4.3 +/- 0.4%; P < 0.01). The postprandial respiratory quotient (RQ) was significantly higher after a LF meal than after a HF meal (0.86 +/- 0.013 vs. 0.83 +/- 0.014; P < 0.001). The HF low carbohydrate meal induced a significantly lower increase in carbohydrate oxidation than the LF meal (20.3 +/- 6.2 vs. 61.3 +/- 7.8 mg/min; P < 0.001). On the contrary, fat oxidation was significantly higher after a HF meal than after a LF meal (-1.3 +/- 2.4 vs. -15.1 +/- 3.6 mg/min; P < 0.01). However, the postprandial fat storage was 8-fold higher after a HF meal than after a LF meal (17.2 +/- 1.7 vs. 1.9 +/- 1.8 g; P < 0.001). These results suggest that a high fat meal is able to induce lower thermogenesis and a higher positive fat balance than an isocaloric and isoproteic low fat meal. Therefore, diet composition per se must be taken into account among the various risk factors that induce obesity in children.     

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.     

Effect of impaired glucose tolerance and type II diabetes on resting metabolic rate and thermic response to a glucose meal in obese women

We examined the hypothesis that patients with impaired glucose tolerance or type II diabetes mellitus have reduced glucose-induced thermogenesis and that this perpetuates obesity in them by reducing energy expenditure. The thermic response after a 75-g glucose meal for 150 minutes was significantly lower in five obese women with diabetes (7.18 +/- 1.8 kcal) and five other obese women with impaired glucose tolerance (6.4 +/- 0.8 kcal) than in five obese women with normal glucose tolerance (16.7 +/- 2.4 kcal) and five lean healthy control subjects (14.0 +/- 2.2 kcal, P less than 0.05). However, obese women with diabetes or impaired glucose tolerance had a significantly higher resting metabolic rate (RMR) (307.0 +/- 9.7 mL O2/min) than predicted for them on the basis of their age, body weight, and total body potassium (274.8 +/- 8.0 mL O2/min, p less than 0.01). The predicted RMR in obese women with normal glucose tolerance test (GTT) (286.0 +/- 5.0 mL O2/min) was not different from their observed RMR (272.0 +/- 6.0). Thus the total energy expenditure during the meal of obese women with diabetes (254 +/- 32 kcal/150 min) and obese women with impaired glucose tolerance (221 +/- 5 kcal/150 min) was higher than that of obese women with normal glucose tolerance (201 +/- 9 kcal/150 min). All three obese groups had a higher total energy expenditure than the lean group (158 +/- 4 kcal/150 min, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Postprandial thermogenesis in leanness and anorexia nervosa.

Resting energy expenditure (REE) and postprandial thermogenesis (PPT) after the ingestion of a mixed test meal (3.56 MJ, 850 kcal) were determined in 7 anorectic patients, 7 very lean women and 8 control women. REE is absolute value was sharply decreased in the anorectics, but did not significantly differ between the very lean and the control subjects. On the other hand, when adjusted for body weight, REE only tended (p = 0.18) to be lower in the anorectics in comparison to the control women. PPT was similar in the anorectics (187.2 +/- 24.6 kJ/4 h) and the controls (200.7 +/- 16.8 kJ/4 h), but lower in the lean subjects (137.5 +/- 20.0 kJ/4h: p less than 0.05) than in the other two groups. The present study shows that the thermic response to the ingestion of a mixed test meal was not decreased in undernourished anorectic patients whereas it was significantly reduced in very lean healthy women.     

Lower excess postexercise oxygen consumption and altered growth hormone and cortisol responses to exercise in obese men

CONTEXT: Obesity is associated with altered patterns of substrate utilization at rest and during exercise. OBJECTIVE: The relationship between obesity and fat oxidation during recovery from exercise was examined. HYPOTHESIS: The postexercise shift toward fat oxidation is blunted in the obese state, reflected by higher respiratory exchange ratio (RER), blunted GH, and increased cortisol values compared with lean controls. DESIGN: Each subject completed two 160-min protocols (baseline and exercise). During baseline, subjects rested for 160 min; during exercise, they completed 30 min of cycling at ventilatory threshold, followed by 130 min of rest. SETTING: This study was performed at the University of Alberta. SUBJECTS: Healthy untrained (maximal oxygen consumption, <45 ml/kg.min or <3.35 liter/min) lean (<16% body fat; n = 6) and obese (>25% body fat; n = 7) men, aged 30-39 yr, were studied. MAIN OUTCOME MEASURES: RER, GH, cortisol, oxygen consumption, heart rate, tympanic temperature, and lactate were obtained during both protocols at matched time intervals and analyzed by repeated measures ANOVA. RESULTS: During baseline, there were no differences detected between lean and obese groups for any of the measured variables. In contrast, during exercise, peak GH levels were blunted (P < 0.05) and cortisol levels were elevated (P < 0.05) in the obese compared with the lean subjects, but RER values were similar in the two groups. The differences in GH and cortisol persisted during the postexercise period accompanied by higher RER values (P < 0.05) and reduced total oxygen consumption (P < 0.05) in the obese group. CONCLUSION: These findings indicate that exercise-induced fat oxidation is diminished in obese men.     

An exercise intervention without weight loss decreases circulating interleukin-6 in lean and obese men with and without type 2 diabetes mellitus

Obesity and type 2 diabetes mellitus (T2DM) have been associated with a state of chronic low-grade inflammation. We examined the effect of exercise without weight loss on circulating inflammatory biomarkers in previously sedentary lean men and obese men with and without T2DM. Middle-aged men (8 lean, 8 obese, and 8 obese with T2DM) performed 60 minutes of aerobic exercise 5 times per week for 12 weeks without a reduction in body weight. Subjects underwent a hyperinsulinemic-euglycemic clamp before and after the 12-week exercise program to assess insulin sensitivity. Circulating interleukin-6 (IL-6), plasminogen activator inhibitor-1 (PAI-1), and C-reactive protein concentrations were measured by sandwich enzyme-linked immunosorbent assay before and after the exercise intervention. Body fat was measured using magnetic resonance imaging, and waist circumference was recorded for each subject pre- and postexercise intervention. Waist circumference and plasma IL-6 concentrations were significantly lower (P < .05) after exercise training despite no change in body weight or insulin sensitivity. There were no correlations between insulin sensitivity and IL-6. Fasting plasma PAI-1 concentration was significantly lower in the lean group compared with the obese group both pre- and postexercise intervention (P < .05). There were no changes in C-reactive protein or PAI-1 concentrations after exercise training. A 12-week exercise intervention led to reductions in waist circumference and fasting IL-6 concentrations in previously sedentary lean and obese men with or without T2DM, demonstrating significant changes in clinically relevant diabetes-related parameters despite no change in body weight.     

Diet-induced thermogenesis and substrate oxidation are not different between lean and obese women after two different isocaloric meals, one rich in protein and one rich in fat

Reduction in diet-induced thermogenesis (DIT) may promote weight gain and maintenance. Data on differences in DIT and macronutrient oxidation between lean and obese subjects are conflicting. In this study, we sought for differences in DIT and macronutrient oxidation between lean and obese women after consumption of 2 different isocaloric meals, one rich in protein and one rich in fat. Fifteen lean and 15 obese women were studied on 2 occasions, 1 week apart. In one visit, they consumed a protein-rich meal; in the other visit, a fat-rich meal. The 2 meals were isocaloric ( approximately 2026 kJ each), of equal volume, and given in random order. Resting energy expenditure and macronutrient oxidation rates were measured and calculated in the fasting state and every 1 hour for 3 hours after meal consumption. Diet-induced thermogenesis was not significantly different between lean and obese subjects after consumption of either the protein-rich (P = .59) or the fat-rich meal (P = .68). Diet-induced thermogenesis was significantly higher (by almost 3-fold) after consumption of the protein-rich meal in comparison with the fat-rich meal in both study groups. In addition, no significant differences in macronutrient oxidation rates were found between lean and obese women after the test meals. The results indicate that DIT is higher after protein intake than after fat intake in both lean and obese participants; however, DIT and macronutrient oxidation rate are not different between lean and obese subjects after consumption of either a protein-rich or a fat-rich meal. Over the long term, a low DIT after regular or frequent fat intake may contribute to the development and maintenance of obesity.     

The effect of a high-carbohydrate meal on postprandial thermogenesis and sympathetic nervous system activity in boys with a recent onset of obesity

The purpose of the present study was to investigate the thermic effect of food (TEF) and sympathetic nervous system (SNS) activity in obese boys. Ten obese (9.2+/-0.4 years) and 13 lean boys (8.8+/-0.4 years) were examined for energy expenditure and fat oxidation measured via indirect calorimetry for 3 hours after a high-carbohydrate (HC; 70% carbohydrate, 20% fat, and 10% protein) or a high-fat (HF; 20% carbohydrate, 70% fat, and 10% protein) meal served on 2 different days at random. The activity of the SNS was assessed by means of a power spectral analysis of the heart rate variability. The TEF, expressed as a percentage of the consumed energy, was significantly lower in obese boys than in lean boys after the HC meal; however, such a difference was not observed after the HF meal. Multiple regression analysis revealed that obesity was a significant variable contributing to the variances in the TEF induced by the HC meal. Moreover, after the HC meal, the boys with a recent onset of obesity (duration, <3 years) manifested a lower TEF as well as a reduced very low frequency component of the heart rate variability, an index of thermoregulatory SNS functions, compared with the remaining obese and lean boys. In conclusion, obese boys possessed normal metabolic and sympathetic responses to the HF meal but showed a diminished thermogenic response to the HC meal, especially during the early phase of obesity.     

Thermic effects of food and exercise in lean and obese women

The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P < 0.005). Exercise potentiated the thermic effect of food for the lean women but not for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P < 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.     

Acute exercise improves postprandial cardiovascular risk factors in overweight and obese individuals

ObjectivesThe effects of 30 min of exercise on postprandial lipaemia in the overweight and obese are unknown as previous studies have only investigated bouts of at least 60 min in lean, healthy individuals. The aim of this study was to investigate whether a single 30-min bout of resistance, aerobic or combined exercise at moderate-intensity would decrease postprandial lipaemia, glucose and insulin levels as well as increase resting energy expenditure and increase fat oxidation following a high fat meal consumed 14 h after the exercise bout, in overweight and obese individuals compared to no exercise. We also compared the effects of the different exercise modalities.MethodsThis study was a randomized cross-over design which examined the postprandial effects of 30 min of different types of exercise in the evening prior to a breakfast meal in overweight and obese men and women. Participants were randomized on four occasions, each one-week apart, to each condition; either no exercise, aerobic exercise, resistance exercise or a combination of aerobic exercise and resistance exercise.ResultsAn acute bout of combination training did not have any significant effect on postprandial measurements compared to no exercise. However, aerobic exercise significantly reduced postprandial triglyceride levels by 8% compared to no exercise (p = 0.02) and resistance exercise decreased postprandial insulin levels by 30% compared to aerobic exercise (p = 0.01).ConclusionThese results indicate that a single moderate-intensity 30 min bout of aerobic or resistance exercise improves risk factors associated with cardiovascular disease in overweight and obese individuals.     

Effects of prior moderate exercise on postprandial metabolism and vascular function in lean and centrally obese men

OBJECTIVES: We investigated whether a session of prior exercise could ameliorate postprandial endothelial dysfunction. BACKGROUND: Endothelial function is impaired after fat ingestion, and this may be related to rises in triglyceride concentrations. Exercise reduces postprandial triglyceride concentrations. METHODS: Ten lean (waist <90 cm) and 10 centrally obese (waist >100 cm) middle-aged men each underwent two oral fat tolerance tests (blood taken fasting and for 8 h after a high-fat meal containing 80 g fat and 70 g carbohydrate). On the afternoon before one test, subjects performed a 90-min treadmill walk (exercise); no exercise was performed before the control test. Endothelium-dependent and -independent microvascular function was assessed using laser Doppler imaging in the fasted state and at two hourly intervals during the 8-h postprandial period. RESULTS: Exercise reduced both fasting and postprandial triglyceride concentrations by 25% in both the lean and centrally obese groups (p < 0.0005). For all subjects taken together, exercise improved fasting endothelium-dependent function by 25% (p < 0.05), and, although there was a significant postprandial decrease in both endothelium-dependent and -independent function in both the control and exercise trials (p < 0.01), postprandial endothelium-dependent and -independent function were 15% and 20% higher, respectively, in the exercise trial than the control trial (both p < 0.05). CONCLUSIONS: A session of prior exercise improves fasting and postprandial vascular function in middle-aged men. This may be one mechanism by which exercise influences cardiovascular risk.     

Long-term effects of low-intensity exercise training on fat metabolism in weight-reduced obese men

The aim of the present study was to investigate the effect of long-term continuation of low-intensity exercise training on weight maintenance, substrate metabolism, and beta-adrenergic-mediated fat oxidation in weight-reduced obese men. Preceding this part of the study, subjects lost 15 +/- 6 kg of body weight by energy restriction with or without low-intensity exercise training. Twenty-nine subjects (diet group, n = 15; diet + exercise group, n = 14) participated in the follow-up study of 40 weeks in which the former diet + exercise group continued their exercise training program. Pre- and postfollow-up, measurements of body weight, body composition, maximal aerobic capacity and substrate oxidation during rest, exercise, and recovery with or without infusion of the beta-adrenergic antagonist, propranolol (PRP), were performed. Over the follow-up period, body weight, fat mass, and fat free mass increased in both groups (P <.0001) without differences between groups. Attendance at exercise training sessions was negatively correlated with regain of body weight (r = -.6, P <.05). Relative fat oxidation, energy expenditure, and beta-adrenergic-mediated fat oxidation during rest, exercise, and recovery were maintained over the follow-up period in both groups. Continuation of low-intensity exercise training after weight reduction did not limit regain of body weight, unless exercise training was frequently performed. Relative (beta-adrenergic-mediated) fat oxidation and energy expenditure were maintained at postdiet level whether or not low-intensity exercise training was performed during follow-up.     

Postprandial thermogenesis is reduced in polycystic ovary syndrome and is associated with increased insulin resistance

OBJECTIVE: In order to investigate the possible causes and effects of obesity in polycystic ovary syndrome resting energy expenditure, postprandial thermogenesis and insulin resistance were measured in 14 polycystic ovary syndrome subjects and in 14 controls. DESIGN: A cross-sectional study of a selected group of patients was performed. PATIENTS: Seven of the PCOS subjects were obese and seven lean. Controls were individually matched for age, race, weight, body mass index (BMI) lean body mass and percentage fat. The obese, but not lean, polycystic ovary syndrome subjects had a greater waist:hip ratio than controls (median (range) obese PCOS 0.865 (0.823-0.960) vs obese control 0.804 (0.823-0.940), P less than 0.025). MEASUREMENTS: Metabolic rate was measured by continuous indirect calorimetry and insulin sensitivity was assessed by a short insulin tolerance test. RESULTS: The resting energy expenditure (REE) was similar in PCOS subjects and controls (median (range), 6796 (5489-7774) vs 6833 (4893-8492) kJ/day). REE correlated with LBM in the PCOS group (r = 0.83, P less than 0.00) and the control group (r = 0.82, P less than 0.001). Postprandial thermogenesis was reduced in polycystic ovary syndrome (obese: median 45.4 (range 33.6-100.0) vs 86.5 (67.2-109.2) kJ (P less than 0.05); lean: 79.4 (73.5-108.4) vs 89.9 (76.0-109.2) kJ (P less than 0.05). Fasting insulin (9.7 +/- 3.6 vs 4.4 +/- 0.8 mU/l, P less than 0.05) and postprandial incremental insulin rise (163 +/- 31 vs 116 +/- 15 mU/l, P less than 0.025) were higher in polycystic ovary syndrome. Insulin sensitivity was reduced in polycystic ovary syndrome (obese: median 136 (range 92-169) vs 173 (109-225) mumol/l/min (P less than 0.05); lean: 161 (138-225) vs 194 (161-253) mumol/l/min (P less than 0.05)). The reduction in insulin sensitivity correlated with the reduced postprandial thermogenesis in the polycystic ovary syndrome group (r = 0.75, P less than 0.01). CONCLUSION: These results confirm previous reports of hyperinsulinaemia and insulin resistance in polycystic ovary syndrome. Furthermore, polycystic ovary syndrome subjects have a reduced postprandial thermogenesis which is related statistically to the reduced insulin sensitivity. The decreased postprandial thermogenesis may predispose women with polycystic ovary syndrome to weight gain.     

Short-term weight loss and exercise training effects on glucose-induced thermogenesis in obese adolescent males during hypocaloric feeding

Our purpose was to examine the effect of short-term weight loss and exercise training on the thermic effect of a glucose load in lean and obese adolescents. Nine obese (age 14.3 +/- 0.3 years, mean +/- s.e.m.) boys were examined during the first (Ob-pre) and sixth (Ob-post) week of caloric restriction (1300-1500 kcal/day, 5441-6279 kJ/day) and aerobic exercise conditioning (walk/jog/swim/calisthenics), and compared to age-matched lean controls (Con). A 100-g oral glucose tolerance test (OGTT) was administered while simultaneously measuring energy expenditure by indirect calorimetry every 30 min for 3 h. Posttest results revealed a decrease in body weight and body fatness in obese boys, but not to the level of that in lean controls (P less than 0.01). The thermic effect of glucose, calculated as the area under the response curve for three hours in excess of resting metabolic rate, was similar in Ob-pre and Con (0.77 +/- 0.14 vs. 0.57 +/- 0.28 kcal/kg lbm/3h), but decreased in Ob-post (0.29 +/- 0.08 kcal/kg lbm/3h, P less than 0.01). The area under the response curve for glucose was elevated in Ob-pre (328.1 +/- 12.2 mg/dl/3h) compared to Con (270.4 +/- 21.4 mg/dl/3h). The insulin response was similar in Ob-pre and Con (120.4 +/- 11.3 vs 125.6 +/- 12.4 mU/ml/3h), but decreased in Ob-post (89.6 +/- 15.1 mU/ml/3h, P less than 0.05). Thus, the improvement in peripheral insulin sensitivity with short-term exercise and weight loss was unaccompanied by favorable alterations in carbohydrate-induced thermogenesis in obese adolescents.