Influence of aerobic capacity, body composition, and thyroid hormones on the age-related decline in resting metabolic rate.

It has been suggested that changes in fat-free weight may not fully explain the decline of resting metabolic rate (RMR) that occurs with aging. We therefore examined the hypothesis that a reduction in maximal aerobic capacity (VO2max) may partially explain the lower RMR in older men, after accounting for differences in fat-free weight and fat weight. We also considered differences in energy intake and plasma thyroid hormones as possible modulators of the age-related decline in RMR in men. Three-hundred healthy men (aged 17 to 78 years) were characterized for: (1) RMR (kcal/min) from indirect calorimetry; (2) body composition from underwater weighing; (3) maximal aerobic capacity from a test of VO2max; (4) plasma thyroid hormones (total triiodothyronine [T3], free T3, total thyroxine [T4], and free T4); and (5) estimated energy intake (kcal/d) from a 3-day food diary. A curvilinear decline of RMR with age was found (P less than .01), in which no relationship was found in men less than 40 years of age (r = .10, slope = 0.002 kcal/min/yr), whereas in men older than 40 years, RMR was negatively related to age (r = -.52, slope = -0.008 kcal/min/yr). After statistical control for differences in fat-free weight and fat weight, a negative relationship between age and RMR persisted (partial r = -.30, P less than .01). It was only after control for fat-free weight, fat weight, and VO2max (partial r = -.10, P greater than .05) that no association between age and RMR was noted.(ABSTRACT TRUNCATED AT 250 WORDS)     

Total energy expenditure and energy requirements in healthy elderly persons.

To investigate energy requirements in healthy elderly subjects, we assessed the association of total energy expenditure (TEE) with resting metabolic rate (RMR), physical activity, body composition, and energy intake in 13 individuals (aged 56 to 78 years, six women and seven men). Free-living TEE was measured using doubly labeled water, RMR was measured by respiratory gas analysis, and energy expenditure of physical activity (EEPA) was derived from the difference between TEE and RMR, assuming the thermic response to feeding contributes 10% of TEE. Fat mass (FM) and fat-free mass (FFM) were obtained from underwater weighing, VO2max was determined from a bicycle test to exhaustion, energy intake was obtained from a 3-day food diary, and leisure time activity (LTA) was determined by structured interview. TEE was 2,406 +/- 438 kcal/d (range, 1,856 to 3,200 kcal/d, or 1.25 to 2.11 times RMR) and was related to VO2max (r = .79, P = .001), LTA (r = .74, P = .004), FFM (r = .69, P = .009), and FM (r = -.64, P = .018). The association between TEE and VO2max persisted after adjustment for FFM (partial r = .58, P = .036). EEPA was related to LTA (r = .83, P less than .0001) and FM (r = -.58, P = .039). Energy intake underestimated TEE by 31% +/- 18% in women and by 12% +/- 11% in men. Using stepwise regression, TEE was best predicted by VO2max and LTA (total adjusted r2 = .86). We conclude the following: (1) TEE varies greatly within healthy elderly subjects due to variations in physical activity; (2) VO2max has an important role in predicting energy requirements in older individuals; and (3) healthy older individuals underreport energy intake.     

The satiating effect of dietary protein is unrelated to postprandial ghrelin secretion

CONTEXT: Increasing dietary protein relative to carbohydrate and fat enhances weight loss, at least in part by increasing satiety. The mechanism for this is unclear. OBJECTIVE: The objective of this study was to compare the effects of isocaloric test meals with differing protein to fat ratios on fasting and postprandial ghrelin, insulin, glucose, appetite, and energy expenditure before and after weight loss on the respective dietary patterns. DESIGN: The study design was a randomized parallel design of 12 wk of weight loss (6 MJ/d) and 4 wk of weight maintenance (7.3 MJ/d) with meals administered at wk 0 and 16. SETTING: The study was performed at an out-patient research clinic. PATIENTS AND OTHER PARTICIPANTS: Fifty-seven overweight (body mass index, 33.8 +/- 3.5 kg/m2) hyperinsulinemic men (n = 25) and women (n = 32) were studied. Interventions: High-protein/low-fat (34% protein/29% fat) or standard protein/high-fat (18% protein/45% fat) diets/meals were given. MAIN OUTCOME MEASURES: The main outcome measures were weight loss and fasting and postprandial ghrelin, insulin, glucose, appetite, and energy expenditure before and after weight loss. RESULTS: Weight loss (9.2 +/- 0.7 kg) and improvements in fasting and postprandial insulin and glucose occurred independently of diet composition. At wk 0 and 16, subjects wanted less to eat after the high-protein/low-fat than the standard protein/high-fat meal (P = 0.02). Fasting ghrelin increased (157.5 +/- 3.4 pg/ml or 46.6 +/- 1.0 pmol/liter; P < 0.001), and the postprandial ghrelin response improved with weight loss (P = 0.043) independently of diet composition. Postprandial hunger decreased with weight loss (P = 0.018) and was predicted by changes in fasting and postprandial ghrelin (r2 = 0.246; P = 0.004). Lean mass was the best predictor of fasting (r2 = 0.182; P = 0.003) and postprandial ghrelin (r2 = 0.096; P = 0.039) levels. CONCLUSIONS: Exchanging protein for fat produced similar weight loss and improvements in metabolic parameters and ghrelin homeostasis. The reduced appetite observed with increased dietary protein appears not to be mediated by ghrelin homeostasis.     

Postabsorptive resting metabolic rate and thermic effect of food in relation to body composition and adipose tissue distribution

One hundred thirty subjects were studied to investigate relationships between the body composition and fat distribution as evaluated by computed tomography and the resting metabolic rate (RMR) as evaluated by indirect calorimetry: 82 premenopausal women (age, 18 to 52 years; body mass index [BMI], 27 to 52 kg/m2), 27 postmenopausal women (46 to 71 years; 28 to 49 kg/m2), and 21 men (18 to 70 years; 31 to 43 kg/m2). The thermic effect of food (TEF) was evaluated in all men and in 2 subgroups of 55 and 19 women. The best-fitting equations for predicting RMR, obtained by multiple regression, included the following as covariates: fat-free mass and both subcutaneous and visceral adipose tissue in premenopausal women (R2 = .55, P = .0001), fat-free mass and visceral adipose tissue in postmenopausal women (R2 = .58, P = .001), and age, with minus sign, and visceral adipose tissue in men (R2 = .44, P = .0051). Fasting insulin and fat-free mass, with minus sign, and both visceral and subcutaneous adipose tissue were the predictors of the TEF (R2 = .25, P = .0055) in premenopausal women. This study demonstrates that visceral fat distribution is important in determining the RMR in postmenopausal women and men. In premenopausal women, total adipose tissue is a main determinant of both the RMR and TEF This last effect could be counterbalanced by insulin resistance.     

Resting energy expenditure, cardiovascular risk factors and insulin resistance in obese patients

OBJECTIVE: The aim of our study was to determine whether energy expenditure modified by increasing body mass over the wide range of body mass index (BMI) was related to insulin resistance, cardiovascular risk factors and dietary intakes. SUBJECTS AND METHODS: A population of 87 obese non-diabetic outpatients was analyzed prospectively. Indirect calorimetry, tetrapolar electrical bioimpedance, serial assessment of nutritional intake using written 3-day food records and biochemical analyses were performed. RESULTS: The mean age was 45.1 +/- 16.7 years and the mean BMI was 35.2 +/- 5.2. Indirect calorimetry showed a resting metabolic rate (RMR) of 1,732.2 +/- 406.6 kcal/day and oxygen consumption of 266.2 +/- 63.3 ml/min. RMR corrected by fat-free mass was 36.8 +/- 14.1 kcal/day/kg. Serial assessment of nutritional intake using written 3-day food records showed a calorie intake of 1,660 +/- 551.7 cal/day, a carbohydrate intake of 168.63 +/- 76.6 g/day, a fat intake of 72.1 +/- 26.42 g/day and a protein intake of 81.1 +/- 23.3 g/day. Insulin, HOMA, systolic blood pressure, diastolic blood pressure, waist circumference, fat mass, waist-to-hip ratio were higher in the third BMI tertile than in the first and second tertiles. No differences were detected in calorie intake, carbohydrate intake, fat intake, protein intake, drinking and alcoholic habit among BMI tertiles. RMR was similar in the different tertiles and the corrected RMR by fat-free mass was higher in first tertile than in the second and third tertiles (44.2 +/- 20.7 vs. 34.5 +/- 9.1 vs. 33.1 +/- 8.5 kcal/kg/day; p < 0.05). In multivariate analysis with a dependent variable (RMR), the fat-free mass remained in the model (F = 7.8; p < 0.05), with an increase of 10.1 (95% CI 3.6-17.5) kcal/day with each 1 kg of fat-free mass adjusted by age and sex. CONCLUSION: Resting energy expenditure in obese patients is not related to the BMI, insulin resistance and dietary intake. RMR is related to fat-free mass in a multivariant model.     

Are aerobically fit older individuals more physically active in their free-living time? A doubly labeled water approach

There is considerable controversy regarding factors regulating free-living physical activity energy expenditure (PAEE) in older individuals. This component is highly variable, is difficult to accurately assess, and reflects both volitional and nonvolitional activities. We examined the association between maximal aerobic fitness (peak VO2) and free-living PAEE in older individuals. One hundred and eighty healthy older patients (96 females and 84 males) between 45-90 yr of age were studied. Total energy expenditure was measured from doubly labeled water. PAEE was calculated as the difference between total energy expenditure, resting metabolic rate, and estimated thermic effect of a meal. Peak VO2 was assessed from an exercise test to volitional fatigue. Fat mass and fat-free mass were assessed from dual energy x-ray absorptiometry. After correction for age, fat mass, and fat-free mass, significant correlations were observed between peak VO2 and PAEE for older males (r = 0.42; P < 0.0001) and females (r = 0.24; P < 0.05), although significant variation among volunteers was noted. When subjects were subdivided by tertiles based on their peak VO2 (liters per min), males with the highest peak VO2 showed greater free-living PAEE than individuals with low peak VO2 (P < 0.01). Similar results were observed in females (P < 0.05). Our results suggest a positive association between higher levels of peak VO2 and greater free-living PAEE in older individuals. This relationship is stronger in older men than in women. These additional energy-dissipating properties during their free-living time may serve to preserve leanness and buffer fat gain with age.     

The influence of the type of dietary fat on postprandial fat oxidation rates: monounsaturated (olive oil) vs saturated fat (cream)

OBJECTIVE: To compare postprandial whole-body fat oxidation rates in humans, following high-fat (43% of total energy) mixed breakfast meals, of fixed energy and macronutrient composition, rich in either monounsaturated fat (MUFA) from extra virgin olive oil or saturated fat (SFA) from cream. DESIGN: Paired comparison of resting metabolic rate (RMR), thermic effect of a meal and substrate oxidation rates following consumption of isocaloric breakfast meals, differing only in the type of fat, administered in random order 1-2 weeks apart. SUBJECTS: Fourteen male volunteers, body mass index (BMI) in the range 20-32 kg/m(2), aged 24-49 y and resident in Melbourne, Australia, were recruited by advertisement in the local media or by personal contact. MEASUREMENTS: Body size and composition was determined by anthropometry and dual energy X-ray absorptiometry (DEXA). Indirect calorimetry was used to measure RMR, thermic effect of a meal, post-meal total energy expenditure and substrate oxidation rate. Blood pressure and pulse rates were measured with an automated oscillometric system. Fasting and 2 h postprandial glucose and insulin concentrations and the fasting lipid profile were also determined. RESULTS: In the 5 h following the MUFA breakfast, there was a significantly greater postprandial fat oxidation rate (3.08+/-4.58 g/5 h, P=0.017), and lower postprandial carbohydrate oxidation rate (P=0.025), than after the SFA breakfast. Thermic effect of a meal was significantly higher (55 kJ/5 h, P=0.034) after the MUFA breakfast, in subjects with a high waist circumference (HWC > or = 99 cm) than those with a low waist circumference (LWC<99 cm). This difference was not detected following the SFA breakfast (P=0.910). CONCLUSION: If postprandial fat oxidation rates are higher after high MUFA, rather than SFA meals, then a simple change to the type of dietary fat consumed might have beneficial effects in curbing weight gain in men consuming a relatively high-fat diet. This may be particularly evident in men with a large waist circumference.     

Fasting and postprandial total ghrelin remain unchanged after short-term energy restriction

Adaptations that promote positive energy balance appear in response to dietary restriction. The aim of this study was to determine whether fasting and postprandial total ghrelin increase in response to short-term energy restriction. Fifteen adult male subjects were subjected to a 4-d energy restricted diet (-800 kcal/d). Body weight and composition, resting energy expenditure, respiratory quotient, fasting and postprandial appetite scores, and fasting and postprandial serum leptin and total ghrelin were determined before and after dietary intervention. Despite the fact that fat mass remained unchanged after the 4 d, fasting (-36%; P 相似文献   

Hormonal and physiological correlates of energy expenditure and substrate oxidation in middle-aged, premenopausal women.

An understanding of the hormonal and physiological correlates of energy expenditure and substrate oxidation in middle-aged women will increase our knowledge of factors that promote changes in energy balance and adiposity. We measured resting and postprandial energy expenditure and substrate oxidation in 59 middle-aged, premenopausal women (mean+/-sD age, 47+/-2 yr) to examine the hormonal and physiological correlates of energy and substrate metabolism. Energy expenditure and substrate oxidation were measured at rest using indirect calorimetry and urinary nitrogen excretion and for 180 min after the ingestion of a liquid meal (10 kcal/kg fat-free mass; 410+/-44 Cal). Fasting hormone levels were measured by RIA, glucose tolerance was determined by a 75-g oral glucose tolerance test, body composition was measured by dual energy x-ray absorptiometry, and peak aerobic capacity was determined by a treadmill test. Using stepwise regression analysis, we found that resting energy expenditure was predicted by fat-free mass and serum leptin concentration (r2 = 66%; P < 0.01), fat oxidation was predicted by resting energy expenditure (r2 = 17%; P < 0.01), and carbohydrate oxidation was predicted by serum leptin and appendicular skeletal muscle mass (r2 = 21%;P < 0.01). Novariables were related to postprandial energy expenditure or substrate oxidation. We conclude that in middle-aged, premenopausal women, variation in resting energy expenditure and substrate oxidation is primarily explained by fat-free mass and serum leptin levels. Thus, changes in metabolically active tissue mass or leptin concentration may partially contribute to changes in resting energy expenditure or substrate oxidation in middle-aged women.     

Energy need in childhood and adult-onset obese women before and after a nine-month nutrition education and walking program

The effect of a 9-month nutrition education and walking program on total calorie need, resting metabolic rate (RMR), thermic effect of food (TEF), body composition, and activity level was determined in seven women (28-41 years of age) with childhood-onset obesity (CO) and eight women (29-42 years of age) with adult-onset obesity (AO). A 3-week testing period was conducted before and after the 9-month program during which all subjects were fed a controlled, weight-maintaining metabolic diet which was used to determine daily calorie need. Body composition, RMR, and TEF were measured during the second and third weeks of both 3-week testing periods. Body weight decreased significantly for CO (mean -5.7 +/- 9.3 kg) and AO (mean -3.3 +/- 6.2 kg), but fat-free mass (FFM) was unchanged. When comparing pre to post data, mean total calorie need increased by 2.9 percent for CO and 3.1 percent for AO (P greater than 0.05), RMR decreased 3.6 percent for CO and 2.8 percent for AO (P less than 0.05), and TEF increased 11 percent for CO and 50 percent for AO (P less than 0.05). Time spent in light and moderate level activity increased significantly from pre to post. The increase in activity and TEF more than compensated for the slight decrease in RMR (mean -55 kcal/day), contributing to an overall increase in daily energy need (mean = 74 kcal/day) at the end of the program, even for the six women who lost greater than 5 kg body weight.     

Ghrelin levels correlate with insulin levels, insulin resistance, and high-density lipoprotein cholesterol, but not with gender, menopausal status, or cortisol levels in humans

The gut peptide, ghrelin, may participate in the control of energy homeostasis and pituitary hormone secretion in humans, stimulating both food intake and, at pharmacological doses, ACTH and cortisol secretion. Meal consumption and weight loss regulate ghrelin levels, but less is known about the relationship of ghrelin to body composition, aging, menopausal status, and lipid metabolism. Therefore, 60 adult men and women of widely varying ages and weights were characterized in terms of body composition and levels of ghrelin, glucose, insulin, lipids, and cortisol. Fasting ghrelin levels correlated positively with age and negatively with BMI and fat cell size, but were not related to fat mass, intraabdominal fat, or lean mass. Fasting ghrelin levels correlated most strongly with insulin levels (r = -0.39; P = 0.002), insulin resistance as determined by the quantitative insulin sensitivity check index (r = 0.38; P = 0.003), and high-density lipoprotein cholesterol levels (r = 0.33; P = 0.009). Meal-induced ghrelin suppression correlated with the postprandial rise in insulin (r = 0.39; P < 0.05). Ghrelin levels were similar in men and women and did not vary by menopausal status or in association with cortisol levels. Our data are consistent with the hypotheses that insulin may negatively regulate ghrelin and that high-density lipoprotein may be a carrier particle for circulating ghrelin.     

Lifestyle behaviours and components of energy balance as independent predictors of ghrelin and adiponectin in young non-obese women

AIM: Dysregulation of the normal levels of ghrelin, leptin and adiponectin in young non-obese subjects could promote food intake, diabetes and cardiovascular disease in later stages of life. Little information is available on how plasmatic concentrations of these hormones may be influenced by eating habits and/or components of energy balance in a young population, which if known, could facilitate their voluntary regulation. METHODS: In this cross-sectional study we examined the predictors of fasting plasma ghrelin, adiponectin and leptin in a population of well-characterized young non-obese women (N = 63). Energy intake was assessed by 24-hour dietary recall, resting metabolic rate (RMR) by indirect calorimetry, physical activity energy expenditure (PAEE) by tri-axial accelerometer, physical fitness by VO(2 peak), and eating behaviors by self administrated questionnaire. RESULTS: Lower RMR and higher HDL-cholesterol were independent predictors of higher plasma ghrelin explaining 17.6% of its variation even after correcting for BMI. Higher total or central fat mass was the only predictor of higher plasma leptin, and no other variable added any power to the prediction equation. Finally, higher energy intake and waist circumference and lower PAEE predicted lower plasma adiponectin in young non-obese women, explaining 43% of the variation in its concentrations even after correcting for total or central fat mass. CONCLUSION: Components of the energy balance (ie: energy intake and/or expenditure) influence adiponectin and ghrelin circulating levels. That is, higher energy intake and lower physical activity independently predict lower adiponectin concentrations, whereas lower resting metabolic rate independently predicts higher ghrelin levels in young non-obese women. Prospective studies are needed to examine whether circulating concentrations of ghrelin and adiponectin can be voluntarily regulated by lifestyle interventions.     

Energy expenditure and physical performance in overweight women: response to training with and without caloric restriction

The metabolic effects of exercise training and the influence of a moderate calorie restriction on the training response were examined in overweight women. Ten healthy women, 119% to 141% of desirable weight, completed the 14-week study. After a 2-week stabilization period, in which diets were designed to maintain body weight (BW), five women were assigned to a 12-week experimental program of diet and exercise (D + EX) that included a 50% reduction in energy intake and a program of moderate intensity aerobic exercise 6 days per week. The other five women were assigned to the same daily exercise (EX) and continued to consume the stabilization diet. Periodic measurements of resting metabolic rate (RMR), thermic effect of food (TEF), energy cost of exercise, and predicted maximal aerobic capacity (VO2 max) were obtained, and the respiratory quotient (RQ) was determined during rest and exercise. Body composition was monitored weekly. Tests of strength and anaerobic capacity were conducted. D + EX lost an average of approximately 1.1 kg/wk, which was 67% fat, 33% lean. EX lost approximately 0.5 kg/wk, which was 86% fat, 14% lean. In both groups, the exercise program resulted in an 11% to 13% improvement in VO2 max and an 8% to 16% decrease in energy expenditure at submaximal workloads. The caloric restriction significantly increased fat utilization during exercise. The RMR declined 9% in D + EX, from 1,550 to 1,411 kcal/d, whereas it was maintained in EX, 1,608 to 1,626 kcal/d. The decrease in RMR observed in D + EX was consistent with the loss of fat-free mass (FFM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum lipids, serum insulin, plasma fibrinogen and aerobic capacity in obese and non-obese Singaporean boys.

OBJECTIVES: To compare blood lipids, lipoproteins, apoproteins, fibrinogen, insulin and aerobic capacity in obese and non-obese Chinese Singaporean boys. To examine relationships between blood metabolites, body composition and aerobic capacity in these groups. DESIGN: Cross-sectional. SUBJECTS: Forty Chinese Singaporean boys aged 13-15 y. Classified as obese (n=20) or non-obese (n=20) based on adiposity (fat mass/fat free mass): >0.60=obese, <0.40=non-obese. MEASUREMENTS: Body composition (dual energy X-ray absorptiometry), waist circumference, peak oxygen consumption (VO(2) peak), serum concentrations of total cholesterol, triacylglycerol, high density lipoprotein cholesterol (HDL-C), total cholesterol/HDL-C, apoproteins AI and B, lipoprotein(a), insulin and glucose. Plasma concentration of fibrinogen. RESULTS: Obese boys had significantly (P<0.01) higher (mean+/-s.d.) concentrations of serum triacylglycerol (1.51+/-0.65 vs 1.04+/-0.34 mmol/l), serum insulin (24.1+/-11.5 vs 12.3+/-4.45 mU/l) and plasma fibrinogen (4.01+/-0.54 vs 3.35+/-0.76 g/l) than non-obese boys. Within the non-obese group plasma fibrinogen concentration was significantly related to percentage body fat (r=0.546, P<0.05). VO(2) peak relative to body mass (ml/kg/min or ml/kg(-0.67)/min) was significantly (P<0.001) lower in obese compared to non-obese boys but absolute VO(2) peak (l/min), adjusted for fat-free mass via analysis of covariance, was higher in obese than non-obese boys (P<0.01). Partial correlations revealed that none of the blood metabolites were significantly related to VO(2) peak independent of body fatness. CONCLUSIONS: Obesity was related to elevated concentrations of serum triacylglycerol, serum insulin and plasma fibrinogen in Chinese Singaporean boys. These elevated concentrations did not appear to be associated with a lower aerobic capacity (independent of body fatness) in the obese.     

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.     

Resting energy metabolism and cardiovascular disease risk in resistance-trained and aerobically trained males

The objectives of this study were (1) to examine differences in resting metabolic rate (RMR) and cardiovascular risk factors among aerobically trained (n = 36), resistance-trained (n = 18), and untrained (n = 42) young males; and (2) to investigate the influence of body composition, dietary intake, and VO2max as possible modulators of differences in cardiovascular risk among groups. Results showed that RMR, adjusted for differences in fat-free weight (FFW), was 5% higher in aerobically trained males compared with resistance-trained males (P < .01), and 10% higher than that in untrained males (P < .01). Plasma levels of cholesterol and low-density lipoprotein cholesterol (LDL-C) were comparable between resistance-trained and aerobically trained males, but were lower (P < .05) than those in untrained males. (The percent intake of dietary fat was related to plasma cholesterol [r = .32, P < .01] and LDL-C [r = .30, P < .01].) When compared with untrained males, fasting triglyceride (TG) levels were 39% and 43% lower (P < .01) in resistance-trained and aerobically trained males, respectively. When compared with untrained males, the fasting insulin to glucose ratio (I/G) was 45% and 53% lower (P < .01) in resistance- and aerobically trained males, respectively. Mean arterial pressure (MAP) was 7% lower (P < .01) in aerobically trained compared with untrained males. Statistical control for differences in percent body fat or percent intake of dietary fat diminished the differences among the groups for plasma lipids, blood pressure, and the I/G ratio. We conclude that aerobically trained and resistance-trained males have higher resting energy requirements independent of FFW compared with untrained males. Aerobically trained and resistance-trained young males have comparable and favorable cardiovascular disease risk profiles compared with untrained males, and this appears to be related to their low level of adiposity and low intake of dietary fat.     

Predictors of postabsorptive ghrelin secretion after intake of different macronutrients

CONTEXT: Release of ghrelin, a gastrointestinal hormone regulating feeding and energy balance, is blunted in obesity, a condition associated with insulin resistance. OBJECTIVE: The objective was to identify anthropometric and metabolic predictors of postabsorptive ghrelin secretion. DESIGN: We evaluated ghrelin, insulin, glucose, and leptin secretion overnight and after intake of different macronutrients. SUBJECTS: Ten obese subjects (age, 31.8 +/- 2.5 yr; body mass index, 43.4 +/- 0.8 kg/m(2)) and six lean subjects (age, 33.5 +/- 2.4 yr; body mass index, 21.8 +/- 1.4 kg/m(2)) participated in the study. MAIN OUTCOME MEASURES: The main outcome measures were resting energy expenditure (REE); fat mass; nighttime approximate entropy (ApEn) and synchronicity (cross-ApEn) of ghrelin, insulin, and leptin; insulin sensitivity by homeostatic model approach insulin-sensitivity (HOMA-S%); postabsorptive area under the curve (AUC); and Delta of ghrelin, insulin, glucose, and leptin after carbohydrate-, lipid-, and protein-rich test meals. RESULTS: Nighttime ApEn scores were higher in obese than lean subjects (P < 0.01). Cross-ApEn revealed a synchronicity between ghrelin-insulin, ghrelin-leptin, and insulin-leptin in both groups. Compared with baseline, ghrelin decreased significantly (P < 0.01) in lean and obese subjects after carbohydrates (42.2 vs. 28.5%; P < 0.05), lipids (40.2 vs. 26.2%; P < 0.01), and proteins (42.2 vs. 26.3%; P < 0.01) devoid of between-meal ghrelin differences. Significant associations occurred between nocturnal ghrelin ApEn and insulin (r = 0.53; P < 0.05), postmeal ghrelin AUCs and REE (r = -0.57; P < 0.05), and HOMA-S% (r = 0.52; P < 0.05), postmeal ghrelin Delta and HOMA-S% (r = 0.60; P < 0.05). REE (beta = -0.57; P = 0.02) and ghrelin ApEn (beta = -0.62; P = 0.01) were predictors of postmeal ghrelin AUC and Delta, respectively. CONCLUSIONS: Obesity determined a decreased orderliness of ghrelin secretion and a relative loss of ghrelin-insulin synchrony. Postabsorptive ghrelin secretion decreased significantly both in obese and lean subjects, was related to insulin sensitivity, and was predicted by energy expenditure and hormone pulsatility.     

Importance of glucagon as a determinant of resting metabolic rate and glucose-induced thermogenesis in obese women

The long-term results of dietary treatment for obesity are often very poor. To predict the effect of a hypocaloric diet, it may be important to consider factors that could influence energy expenditure, especially those altered in obesity. Elevated plasma levels of glucagon are associated with obesity. In this study, the relationship of glucagon to resting metabolic rate (RMR) and glucose-induced thermogenesis (GIT) has been investigated. RMR and GIT, after ingesting 100 g glucose, were measured by indirect calorimetry in 25 obese premenopausal women (body mass index [BMI], 37.2 +/- 4.7 kg.m-2). RMR was significantly related to fat-free mass (FFM) (r = .50, P less than .005). A significant relation could be found between RMR and fasting glucagon levels (r = .36, P less than .05). Plasma glucose and insulin levels were not predictive for RMR. Mean GIT increased with increasing waist-hip circumference ratio (WHR) (r = .71, P less than 0.0001), confirming previous findings of our group. No relation was found between GIT and glucagon levels, neither in the basal state nor after glucose. The only important metabolic determinant was area under the curve (AUC) for glucose (r = .45, P less than .01), suggesting a higher GIT in obese women with impaired glucose intolerance. This suggests that the control of energy metabolism by the concentration of glucagon may be more important in the fasting state than after a meal. Plasma glucagon concentration should be considered in the evaluation of RMR.     

Intact sympathetic nervous system is required for leptin effects on resting metabolic rate in people with spinal cord injury

Compared with able-bodied (AB), people with spinal cord injury (SCI) have a 3- to 5-fold higher risk of developing type 2 diabetes mellitus, which may be associated with increased fat mass. Evidence suggests that leptin regulates body adiposity through the sympathetic nervous system, which is impaired in people with high lesion SCI. The purpose of this study was to determine the relationship among leptin levels, body composition, and resting metabolic rate (RMR) in people with high lesion SCI and body mass index-, weight-, height-, and waist circumference-matched AB subjects. Fourteen subjects (seven SCI and seven AB) participated in the study. After an overnight fast, various hormones, glucose, and RMR were measured. There was no significant difference in plasma glucose, insulin, GH, cortisol, and glucagon levels between the two groups. The SCI group had 105% higher plasma leptin levels than the AB group (P < 0.05). Plasma leptin levels correlated with body mass index (SCI: r = 0.80; P = 0.028; AB: r = 0.79; P = 0.035) and fat mass (SCI: r = 0.95; P = 0.001; AB: r = 78; P = 0.038) in both groups. The plasma leptin level correlated with the absolute RMR (SCI: r = 0.15; P = 0.75; AB: r = 0.99; P < 0.006) and the RMR per unit fat-free mass (SCI: r = -0.70; P < 0.08; AB: r = 0.845; P < 0.017) in the AB group, but not in the SCI group. The absolute RMR was significantly reduced in the SCI group compared with the AB group, but there was no difference in the relative RMR between the groups. In conclusion, the SCI group has a significantly higher plasma leptin level than the AB group. The absolute and relative RMR correlated with leptin only in the AB group.