Basal and postprandial substrate oxidation rates in obese women receiving two test meals with different protein content

BACKGROUND & AIMS: Fuel utilisation and storage in lean and obese subjects seem to be differently affected by the macronutrient distribution intake. The aim of this intervention study was to explore the extent to which the fat mass status and the macronutrient composition of an acute dietary intake influence substrate oxidation rates. METHODS: Fuel utilisation in 26 women, 14 obese (BMI = 37.1 +/- 1.1 kg/m2) and 12 lean (BMI = 20.6 +/- 0.5 kg/m2) was measured over 6 h to compare the metabolic effect of a single balanced protein (HC) meal and a high protein (HP) single meal, which were designed to supply similar energy contents (1672 kJ). The macronutrient composition as a percentage of energy of the HC meal was 55% carbohydrate, 15% protein and 30% fat, while the HP meal contained 40% carbohydrate, 30% protein and 30% fat. Nutrient oxidation rates and energy expenditure were calculated by indirect calorimetry (hood system), whereas exogenous amino acid oxidation was estimated from the 13C isotopic enrichment of breath after oral administration of L[1-13C]leucine. RESULTS: Fasting lipid oxidation was higher in the obese than in the lean women (P < 0.05), and it was significantly correlated with body fatness (P < 0.01). A single HP meal consumption produced higher postprandial fat oxidation as compared with HC meal intake (P < 0.02), in both obese and lean subjects, with no apparent changes in glucose oxidation rates. Furthermore, postprandial fat utilisation after the test meal intake was higher in obese than in the lean women (P < 0.01). The time course of 13CO2 in breath followed a similar pattern in both dietary groups, although a non-statistically significant higher trend in protein and 13C-leucine oxidation was found in the HP group. CONCLUSIONS: Net lipid oxidation depends on both short-term dietary composition intake and fat body mass, being significantly higher after a relatively high protein meal as compared to a balanced diet intake and in obese women as compared to lean controls.     

De novo lipogenesis during controlled overfeeding with sucrose or glucose in lean and obese women.

BACKGROUND: The results of previous studies suggest that de novo lipogenesis may play an important role in the etiology of obesity, particularly during overconsumption of different carbohydrates. OBJECTIVE: We hypothesized that de novo lipogenesis would increase during overfeeding, would vary depending on the type of carbohydrate consumed, and would be greater in obese than in lean women. DESIGN: De novo lipogenesis was measured during 96 h of overfeeding by 50% with either sucrose or glucose and during an energy balance treatment (control) in 8 lean and 5 obese women. De novo lipogenesis was determined by measuring the amount of deuterium incorporation into plasma triacylglycerols. Fat and carbohydrate balance were measured simultaneously by continuous whole-body calorimetry. RESULTS: De novo lipogenesis did not differ significantly between lean and obese subjects, except with the control treatment, for which de novo lipogenesis was greater in the obese subjects. De novo lipogenesis was 2- to 3-fold higher after overfeeding by 50% than after the control treatment in all subjects. The type of carbohydrate overfeeding (sucrose or glucose) had no significant effect on de novo lipogenesis in either subject group. Estimated amounts of absolute VLDL production ranged from a minimum of 2 g/d (control) to a maximum of 10 g/d after overfeeding. This compares with a mean fat balance of approximately 275 g after 96 h of overfeeding. Individual subjects showed characteristic amounts of de novo lipogenesis, suggesting constitutive (possibly genetic) differences. CONCLUSION: De novo lipogenesis increases after overfeeding with glucose and sucrose to the same extent in lean and obese women but does not contribute greatly to total fat balance.     

Fat and carbohydrate balances during adaptation to a high-fat

BACKGROUND: Dietary fat contents are highly variable. Failure to compensate for the positive fat balance that occurs during the shift to a high-fat, low-carbohydrate diet by increasing energy expenditure or by decreasing food intake may result in the gain of fat mass. OBJECTIVE: The objective of this study was to investigate the time course of fat oxidation during adaptation to an isoenergetic high-fat, low-carbohydrate diet. DESIGN: After a 5-d control diet, dietary fat was increased from 37% of energy to 50% of energy for 4 d in 6 healthy, young lean men. Respiratory quotient and substrate macronutrient oxidation and balance were measured in a respiratory chamber. Fasting concentrations of insulin, glucose, and triacylglycerol; maximal oxygen consumption (f1.gif" BORDER="0">O(2)max) during treadmill exercise; and free-living energy expenditure were determined. Body fat was measured by dual-energy X-ray absorptiometry and visceral adipose tissue by computerized tomography. RESULTS: Compared with the baseline diet, the high-fat, low-carbohydrate diet resulted in positive fat and protein balances and a negative carbohydrate balance. Insulin concentration and the postabsorptive respiratory quotient were positively correlated with the fat balance during the high-fat, low-carbohydrate diet, whereas f1.gif" BORDER="0">O(2)max during treadmill exercise was negatively related to fat balance. With use of stepwise regression, f1.gif" BORDER="0">O(2)max was the best predictor of fat balance. There was a negative correlation between fat balance and carbohydrate balance (r(2) = 0.88). CONCLUSION: Both baseline insulin concentration and f1.gif" BORDER="0">O(2)max during treadmill exercise predict fat balance during the shift to a high-fat diet under isoenergetic conditions.     

Obesity: an inherited metabolic deficiency in the control of macronutrient balance?

It has generally been assumed that the body is 'energy blind' and calories from all three macronutrients contribute with the same value to energy balance. There is, however, accumulating evidence to suggest that during ad-libitum conditions energy balance is achieved by a separate regulation of carbohydrate, fat and protein balances. Regulation of carbohydrate balance has the highest priority in the hierarchy, which is appropriate because the limited glycogen stores are only capable of covering the carbohydrate oxidation for a few days. Due to the higher satiating power of carbohydrate and protein compared with fat, a reduction in the dietary fat/carbohydrate ratio produces a negative fat balance in normal subjects consuming the diet ad libitum, while an increase in dietary fat/carbohydrate ratio results in a positive fat balance and weight gain. Subjects with a genetically determined predisposition to obesity become obese when they are exposed to a particular range of environmental conditions. The available knowledge suggests that the genetic propensity to weight gain is caused by a susceptibility to dietary fat due to an impaired capacity to increase their lipid/carbohydrate oxidation when fed a high-fat/low-carbohydrate diet. This in turn promotes lipid storage, depletion of carbohydrate stores and increases appetite. By enlarging the fat stores, the accompanying insulin resistance and higher levels of circulating non-esterified fatty acids increase lipid oxidation until it is commensurate with the dietary fat intake. The development of obesity may therefore be viewed as a regulatory mechanism by which the impaired lipid oxidation rate is raised to match a high fat intake. However, by decreasing the dietary ratio of fat to carbohydrate, macronutrient balance may be achieved with a high energy expenditure and a normal body composition. The results support current dietary recommendations, but with less emphasis on carbohydrate source, and they are also applicable for the prevention and treatment of obesity.     

Postprandial de novo lipogenesis and metabolic changes induced by a high-carbohydrate, low-fat meal in lean and overweight men

BACKGROUND: Adjustments of carbohydrate intake and oxidation occur in both normal-weight and overweight individuals. Nevertheless, the contribution of carbohydrates to the accumulation of fat through either reduction of fat oxidation or stimulation of fat synthesis in obesity remains poorly investigated. OBJECTIVE: The objective of this study was to assess the postprandial metabolic changes and the fractional hepatic de novo lipogenesis (DNL) induced by a high-carbohydrate, low-fat meal in lean and overweight young men. DESIGN: A high-carbohydrate, low-fat meal was administered to 6 lean and 7 overweight men after a 17.5-h fast. During the fasting and postprandial periods, energy expenditure (EE), macronutrient oxidation, diet-induced thermogenesis, and serum insulin, glucose, triacylglycerol, and fatty acids were measured. To determine DNL, [1-13C]sodium acetate was infused and the mass isotopomer distribution analysis method was applied. RESULTS: After intake of the high-carbohydrate meal, the overweight men had hyperinsulinemia and higher fatty acid and triacylglycerol concentrations than did the lean men. The overweight group showed a greater EE, whereas there was no significant difference in carbohydrate oxidation between the groups. Nevertheless, the overweight men had a marginally higher protein oxidation and a lower lipid oxidation than did the lean men. DNL was significantly higher before and after meal intake in the overweight men and was positively associated with fasting serum glucose and insulin concentrations. Furthermore, postprandial DNL was positively correlated with body fat mass, EE, and triacylglycerol. CONCLUSION: After a high-carbohydrate, low-fat meal, overweight men had a lower fat oxidation and a higher fractional hepatic fat synthesis than did lean men.     

Hunger disease

This paper examines three aspects of hunger disease: the effect of initial fat stores on macronutrient fuel selection during total starvation (no energy) and how it influences survival; the effects of different rates of weight loss on tissue and body function; and the importance of appetite sensations, including hunger, during malnutrition and during enteral and parenteral nutritional support. Long-term starvation studies in humans reveal major differences in fat carbohydrate and protein metabolism between lean and obese subjects, including a 2-4-fold lower contribution of protein oxidation to energy expenditure in obese subjects, which ensures that more of the excess body fat is oxidized. The rate of weight loss, determined by recent dietary intake, can have major effects on tissue and body function, including wound healing, the acute phase protein response, muscle fatigue and psychological/behavioural function in both clinical and non-clinical settings. In depleted states uncomplicated by disease, changes in appetite sensations can result in energy intakes as high as 6000 to 10,000 kcal/day ( 25-42 MJ/day). Long-term enteral tube feeding and parenteral nutrition are associated with frequent disturbances in appetite sensations, and in those able to eat normally they tend to add rather than replace oral intake to an extent that appears to depend on the regimen. It is concluded that 1) differences between lean and obese subjects in macronutrient fuel selection during starvation are adaptive because they optimize survival in both groups of subjects; 2) the rate of weight loss in health and disease has a major effect on certain tissue and body functions, independently of the magnitude of weight loss; and 3) clinically relevant disturbances in appetite sensations are common subjects receiving long-term enteral and parenteral nutrition. The clinical modulation of all these variables would be aided by greater knowledge of the mechanisms involved.     

Differences in short-term metabolic responses to a lipid load in lean (resistant) vs obese (susceptible) young male subjects with habitual high-fat consumption

OBJECTIVE: To determine the role of macronutrients oxidation ability in the postprandial response to a high lipid load in the mechanisms conferring resistance or susceptibility to obesity. SUBJECTS AND DESIGN: Nine lean and nine obese young male subjects with habitual similar high-fat intake (>40 % of energy) and comparable physical activity were selected and categorized as 'resistant', those who remained lean (body mass index (BMI) <25 kg/m2), and 'susceptible', those who were obese (BMI>30 kg/m2). Fasting blood samples were taken for the evaluation of blood metabolic and hormonal variables. Resting metabolic rate (RMR) and substrates oxidation were measured by indirect calorimetry, in the fasting state and every 30 min for 3 h after a rich lipid meal (fat 94.7%) supplied to cover the 50% of the volunteers energy requirements. The study was performed at the Metabolic Unit of the University of Navarra. RESULTS: Fasting RMR and lipid oxidation were higher in obese-susceptible subjects. However, similar values were found in both groups after adjustment for fat mass and free fat mass. The cumulative postprandial fat oxidation was also similar in both groups (despite having different tissue metabolic activity), whereas cumulative carbohydrate oxidation was lower in the obese-susceptible group. The thermic effect of food (% of dietary induced thermogenesis) was lower (P<0.05) in the susceptible-obese subjects. The energy and fat balance were more positive in the obesity-susceptible individuals after the high fat load, who also showed higher fasting homeostatic model assessment index, low-density lipoprotein-cholesterol and triacylglyceride levels, hyperleptinemia and hypoadiponectinemia. CONCLUSION: Lean-resistant individuals came closer to achieving fat balance than obese-susceptible subjects. These metabolic and hormonal differences are probably genetically determined.     

Effect of carbohydrate overfeeding on whole body and adipose tissue metabolism in humans

OBJECTIVE: To evaluate the effect of a 4-day carbohydrate overfeeding on whole body net de novo lipogenesis and on markers of de novo lipogenesis in subcutaneous adipose tissue of healthy lean humans. RESEARCH METHODS AND PROCEDURES: Nine healthy lean volunteers (five men and four women) were studied after 4 days of either isocaloric feeding or carbohydrate overfeeding. On each occasion, they underwent a metabolic study during which their energy expenditure and net substrate oxidation rates (indirect calorimetry), and the fractional activity of the pentose-phosphate pathway in subcutaneous adipose tissue (subcutaneous microdialysis with 1,6(13)C2,6,6(2)H2 glucose) were assessed before and after administration of glucose. Adipose tissue biopsies were obtained at the end of the experiments to monitor mRNAs of key lipogenic enzymes. RESULTS: Carbohydrate overfeeding increased basal and postglucose energy expenditure and net carbohydrate oxidation. Whole body net de novo lipogenesis after glucose loading was markedly increased at the expense of glycogen synthesis. Carbohydrate overfeeding also increased mRNA levels for the key lipogenic enzymes sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase, and fatty acid synthase. The fractional activity of adipose tissue pentose-phosphate pathway was 17% to 22% and was not altered by carbohydrate overfeeding. DISCUSSION: Carbohydrate overfeeding markedly increased net de novo lipogenesis at the expense of glycogen synthesis. An increase in mRNAs coding for key lipogenic enzymes suggests that de novo lipogenesis occurred, at least in part, in adipose tissue. The pentose-phosphate pathway is active in adipose tissue of healthy humans, consistent with an active role of this tissue in de novo lipogenesis.     

Leptin levels are associated with fat oxidation and dietary-induced weight loss in obesity

OBJECTIVE: To examine the relationship between fasting plasma leptin and 24-hour energy expenditure (EE), substrate oxidation, and spontaneous physical activity (SPA) in obese subjects before and after a major weight reduction compared with normal weight controls. To test fasting plasma leptin, substrate oxidations, and SPA as predictive markers of success during a standardized weight loss intervention. RESEARCH METHODS AND PROCEDURES: Twenty-one nondiabetic obese (body mass index: 33.9 to 43.8 kg/m(2)) and 13 lean (body mass index: 20.4 to 24.7 kg/m(2)) men matched for age and height were included in the study. All obese subjects were reexamined after a mean weight loss of 19.2 kg (95% confidence interval: 15.1-23.4 kg) achieved by 16 weeks of dietary intervention followed by 8 weeks of weight stability. Twenty-four-hour EE and substrate oxidations were measured by whole-body indirect calorimetry. SPA was assessed by microwave radar. RESULTS: In lean subjects, leptin adjusted for fat mass (FM) was correlated to 24-hour EE before (r = -0.56, p < 0.05) but not after adjustment for fat free mass. In obese subjects, leptin correlated inversely with 24-hour and resting nonprotein respiratory quotient (r = -0.47, p < 0.05 and r = -0.50, p < 0.05) both before and after adjustments for energy balance. Baseline plasma leptin concentration, adjusted for differences in FM, was inversely related to the size of weight loss after 8 weeks (r = -0.41, p = 0.07), 16 weeks (r = -0.51, p < 0.05), and 24 weeks (r = -0.50, p < 0.05). DISCUSSION: The present study suggests that leptin may have a stimulating effect on fat oxidation in obese subjects. A low leptin level for a given FM was associated with a greater weight loss, suggesting that obese subjects with greater leptin sensitivities are more successful in reducing weight.     

Post-exercise substrate utilization after a high glucose vs. high fructose meal during negative energy balance in the obese

OBJECTIVE: To assess the effects of negative energy balance on the metabolic response of a meal containing either glucose or fructose as the primary source of carbohydrate after exercise in obese individuals in energy balance, or negative energy balance. RESEARCH METHODS AND PROCEDURES: Fourteen adults with mean body mass index (BMI) 30.3 +/- 1 kg/m2, age 26 +/- 2 years, and weight 93.5 +/- 5.4 kg, adhered to an energy-balanced (EB) or a negative energy-balanced (NEB) diet for 6 days. On Day 7, subjects exercised at 70% VO2peak for 40 minutes then consumed either high glucose (50 g of glucose, HG) or high fructose (50 g of fructose, HF) liquid meal. Substrate utilization was measured by indirect calorimetry for 3 hours. Blood samples were collected before exercise and 0, 30, 60, 120, and 180 minutes after consuming the meal. RESULTS: The HG produced 15.9% greater glycemic (p < 0.05) and 30.9% larger insulinemic (p < 0.05) responses than the HF under both EB and NEB conditions. After the NEB diet, carbohydrate and fat oxidation did not differ for HG and HF. In contrast, carbohydrate oxidation increased 31%, and fat oxidation decreased 39% with HF compared with HG after the EB diet. Thus, HF and HG consumed after exercise produced marked differences in macronutrient oxidation when obese subjects followed an EB diet, but no difference when adhering to a NEB diet. DISCUSSION: The data suggest that the use of fructose in supplements/meals may provide no additional benefit in terms of substrate utilization during a weight loss program involving diet and exercise.     

Diacylglycerols affect substrate oxidation and appetite in humans

BACKGROUND: Meals rich in diacylglycerols (DGs) instead of triacylglycerols (TGs) show beneficial effects on lipid metabolism and energy balance. These effects are probably attributable to differences in DG and TG metabolism, especially postprandial fat oxidation. OBJECTIVE: We assessed the effects of partial replacement of TGs with DGs on substrate oxidation, energy expenditure (EE), relevant blood variables, and appetite. DESIGN: Twelve healthy, dietarily unrestrained women participated in a single-blind, placebo-controlled, randomized trial with crossover design. For 3 d before and throughout a 36-h stay in a respiration chamber, subjects were fed energy-maintenance amounts of a diet consisting of 55% of energy from carbohydrate, 15% from protein, and 30% from fat. In the respiration chamber, 40% of the fat was consumed as DG-rich (80% DGs) oil or as TG-based control oil with a similar fatty acid profile. RESULTS: Fat oxidation was significantly higher with DG treatment than with TG treatment. Appetite profiles during day 1 (24 h) did not differ significantly between the DG and TG treatments; however, feelings of hunger, appetite, estimated prospective food intake, and desire to eat were all significantly lower on day 2 (12 h) with DG treatment. Mean plasma beta-hydroxybutyrate tended to be higher with DG treatment, and the difference between the 2 treatments was significant at 1130 on day 2. Plasma lipid concentrations and resting and 24-h EE did not differ significantly between the 2 treatments. CONCLUSION: Consumption of DGs in place of TGs does not alter EE but produces metabolic effects, particularly increases in fat oxidation, which may be associated with improved appetite control and energy balance.     

Macronutrients and appetite control with implications for the nutritional management of the malnourished

Altered appetite is one of the most frequently cited yet poorly understood symptoms encountered in the clinical setting. This review critically discusses the constraints under which macronutrient balance is physiologically regulated, the nature of appetite control and feeding behaviour in humans, how dietary macronutrients influence appetite control and feeding behaviour, the role of macronutrient metabolism and stores as putative signals that can influence appetite, energy intake and balance, and the importance of studying undernutrition as a reference for studies of appetite in the clinical setting in order to develop effective therapies for malnutrition (over and undernutrition). The following general conclusions were reached: (1) there seems to be a hierarchy in the extent to which individual macronutrient balances are regulated and the extent to which dietary macronutrients suppress subsequent energy intake (in both cases protein >carbohydrate>fat); (2) the oxidation of individual nutrients is monitored both by the central and peripheral nervous system but the relative importance of the two systems is unclear; (3) recent work on body weight regulation has placed much more emphasis on signals arising from adipose tissue than other potentially powerful signals arising from lean tissue; (4) in disease-related malnutrition, loss of both lean and adipose tissue is often not associated with increased appetite sensations and food intake probably because of complex interactions between inflammatory mediators such as cytokines, neuroendocrine abnormalities, drug (and other) therapies, and incompletely understood effects of psychological and metabolic disturbances.     

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.     

Differences in postprandial responses to fat and carbohydrate loads in habitual high and low fat consumers (phenotypes)

The present study investigated metabolic responses to fat and carbohydrate ingestion in lean male individuals consuming an habitual diet high or low in fat. Twelve high-fat phenotypes (HF) and twelve low-fat phenotypes (LF) participated in the study. Energy intake and macronutrient intake variables were assessed using a food frequency questionnaire. Resting (RMR) and postprandial metabolic rate and substrate oxidation (respiratory quotient; RQ) were measured by indirect calorimetry. HF had a significantly higher RMR and higher resting heart rate than LF. These variables remained higher in HF following the macronutrient challenge. In all subjects the carbohydrate load increased metabolic rate and heart rate significantly more than the fat load. Fat oxidation (indicated by a low RQ) was significantly higher in HF than in LF following the fat load; the ability to oxidise a high carbohydrate load did not differ between the groups. Lean male subjects consuming a diet high in fat were associated with increased energy expenditure at rest and a relatively higher fat oxidation in response to a high fat load; these observations may be partly responsible for maintaining energy balance on a high-fat (high-energy) diet. In contrast, a low consumer of fat is associated with relatively lower energy expenditure at rest and lower fat oxidation, which has implications for weight gain if high-fat foods or meals are periodically introduced to the diet.     

Effects of leptin resistance on acute fuel metabolism after a high carbohydrate load in lean and overweight young men.

OBJECTIVE: Six lean (BMI = 20.8 +/- 0.7) and seven overweight (BMI = 30.8 +/- 1.7) young men (18-27 years old) were studied to investigate the acute effect of a high-carbohydrate meal on leptin levels and its relation to energy expenditure as well as to protein, carbohydrate and fat oxidation. METHODS: Study participants were given a high-carbohydrate meal (17% as protein, 80% as carbohydrates and 3% as lipids) covering 40% of their estimated daily energy requirements. Serum leptin. insulin. glucose, free fatty acids and triglycerides levels were measured before meal intake and during the frour postprandial hours. Furthermore, energy expenditure (EE), protein, carbohydrate and lipid oxidation were measured in fasted and fed conditions. RESULTS: Fasting leptin was found to be positively correlated with circulating insulin concentrations (r = .748; p = 0.011) and body fat in kg (r = .827; p = 0.001). During the measured postprandial period no statistically significant changes were found in leptin levels as compared with pre-meal values in either lean or overweight men, nor differences in leptin changes between both groups. After load intake, carbohydrate oxidation was lower in overweight individuals (p < 0.05). while no significant differences were observed in protein oxidation. Cumulative lipid oxidation was found to be negatively associated with post-meal leptin values, being significantly lower in the overweight as compared with lean men (p < 0.05). This study demonstrates that the acute postprandial fuel substrate utilization is altered in overweight men with a lower carbohydrate oxidation and a strong inhibition of lipid oxidation, which could be attributed to some leptin resistance. CONCLUSION: These data also suggest that short-term meal-related metabolic responses may explain the long-term body adiposity if they are sustained over long intervals.     

Glutamine supplementation increases postprandial energy expenditure and fat oxidation in humans

BACKGROUND: Glutamine interacts with insulin-mediated glucose disposal, which is a component of the increase in energy expenditure (EE) after a meal. The study aim was to examine if glutamine supplementation alters postmeal nutrient oxidation. METHODS: Ten healthy young adults consumed a mixed meal (6.5 kcal/kg, 14%:22%:64% = protein:fat:carbohydrate) containing either glutamine (GLN:1.05 kcal/kg) or an isocaloric amino acid mixture (alanine: glycine:serine = 2:1:0.5; CON). GLN and CON treatments were administered on separate days in random order for each subject. EE, nonprotein respiratory quotient (RQ), and fat and carbohydrate oxidation rates were assessed using indirect calorimetry for 30 minutes before and for 360 minutes after meal ingestion. RESULTS: Premeal EE and RQ were similar between treatments. The increase in EE above basal during both early (0-180 minutes) and late (180-360 minutes) postmeal phases was greater in GLN than in CON (p < .05), resulting in postmeal EE being 49% greater during the total postmeal phase (p < .05). Net change of carbohydrate oxidation was 38% higher during the early phase with GLN (p < .05), whereas it was 71% lower during the later phase (p < .05). GLN enhanced fat oxidation by approximately 42 kcal compared with CON during the late phase (p < .05). CONCLUSIONS: Glutamine supplementation with a mixed meal alters nutrient metabolism to increase postmeal EE by increasing carbohydrate oxidation during the early postmeal phase and fat oxidation during the late postmeal phase. Consideration must be given to the potential that these postprandial changes in EE are related to glutamine-mediated changes in insulin action and consequently glucose disposal.     

Meals with similar energy densities but rich in protein,fat, carbohydrate,or alcohol have different effects on energy expenditure and substrate metabolism but not on appetite and energy intake

BACKGROUND: It has been suggested that the satiating power of the 4 macronutrients follows the oxidation hierarchy: alcohol > protein > carbohydrate > fat. However, the experimental evidence for this is still scarce. OBJECTIVE: The goal was to investigate the effects on appetite, energy intake and expenditure, and substrate metabolism of meals rich in 1 of the 4 macronutrients. DESIGN: Subjective appetite sensations, ad libitum food intake, energy expenditure, substrate metabolism, and hormone concentrations were measured for 5 h after breakfast meals with similar energy density and fiber contents but rich in either protein (32% of energy), carbohydrate (65% of energy), fat (65% of energy), or alcohol (23% of energy). Subjects were normal-weight, healthy women (n = 9) and men (n = 10) studied in a crossover design. RESULTS: There were no significant differences in hunger or satiety sensations or in ad libitum energy intake after the 4 meals. Diet-induced thermogenesis was larger after the alcohol meal (by 27%; P < 0.01), whereas protein produced an intermediary response (17%; NS) compared with carbohydrate and fat (meal effect: P < 0.01). After the alcohol meal, fat oxidation and leptin concentrations were greatly suppressed (meal effects, P < 0.0001 and P < 0.05) and triacylglycerol concentrations were as high as after the fat meal. CONCLUSION: Intake of an alcohol-rich meal stimulates energy expenditure but suppresses fat oxidation and leptin more than do isoenergetically dense meals rich in protein, carbohydrate, or fat. Despite differences in substrate metabolism and hormone concentrations, satiety and ad libitum energy intake were not significantly different between meals. Our data, therefore, do not support the proposed relation between the macronutrient oxidation hierarchy and the satiety hierarchy.     

Concurrent physical activity increases fat oxidation during the shift to a high-fat diet

BACKGROUND: It takes several days to adapt to a high-fat diet. In an earlier study, we observed a large degree of interindividual variation in the capacity to adapt to a high-fat diet. We hypothesized that concurrent physical activity would accelerate fat oxidation during an isoenergetic high-fat diet. OBJECTIVE: The objective of this study was to determine the effect of increased physical activity on the ability of young healthy men to increase fat oxidation during the shift to a high-fat diet. DESIGN: Six young healthy men participated in a randomized, single-blind crossover study. The volunteers consumed a diet contributing 37% of energy as fat, 14% as protein, and 49% as carbohydrate for 4 d. Energy expenditure and macronutrient balance were then measured in a respiration chamber as the energy content of the isoenergetic diet was changed to 50% fat, 14% protein, and 36% carbohydrate. Treadmill walking, as the physical activity, was used to increase total daily energy expenditure to 1.8 times the resting metabolic rate during 1 of 2 stays in the metabolic chamber. Total daily energy expenditure was maintained at 1.4 times the resting metabolic rate for the other stay. RESULTS: Energy balance was not significantly different between the 2 conditions. The 24-h respiratory quotient decreased more rapidly and to a greater extent under conditions of increased energy expenditure. Further, there was a decrease in the interindividual variability in the response of the respiratory quotient to a high-fat diet with increased energy expenditure (physical activity). Cumulative carbohydrate and protein balances were greater under conditions of increased physical activity. Conversely, cumulative fat balance was greater under sedentary conditions. CONCLUSION: Concurrent physical activity increases fat oxidation during the shift to a high-fat diet.     

Metabolic effects of mental stress during over- and underfeeding in healthy women.

OBJECTIVE: To assess the short-term consequences of carbohydrate or fat overfeeding or of food restriction on the metabolic effects of mental stress in healthy lean women. RESEARCH METHODS AND PROCEDURES: The effects of a sympathetic activation elicited by mental stress were evaluated in a group of healthy women after standardized isocaloric feeding (ISO) or after a 3-day overfeeding with 40% excess calories as either carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). Oxygen consumption rate (VO(2)) was measured as an index of energy expenditure, and subcutaneous glycerol concentrations were monitored with microdialysis. The same measurements were performed in another group of healthy women after ISO and after a 3-day period of underfeeding with a protein sparing modified fast (UF). RESULTS: In all conditions, mental stress significantly increased heart rate, blood pressure, plasma norepinephrine and epinephrine concentrations, and VO(2), and produced a nonsignificant increase in subcutaneous glycerol concentrations. CHO OF and FAT OF did not alter the effects of mental stress on VO(2) and subcutaneous glycerol concentrations. In contrast, UF increased basal VO(2) but significantly reduced its stimulation by mental stress. UF also enhanced the increase in subcutaneous glycerol concentrations during mental stress. DISCUSSION: UF reduces the stimulation of energy expenditure and enhances lipolysis during sympathetic activation. These adaptations may be involved in mobilization of endogenous fat while limiting weight loss. In contrast, short-term overfeeding fails to alter the sympathetic control of energy expenditure and lipolysis.     

Nutrient balance and energy expenditure during ad libitum feeding of high-fat and high-carbohydrate diets in humans.

To study the influence of diet composition on regulation of body weight, we fed 21 weight-stable subjects (11 lean, 10 obese) high-carbohydrate (HC) and high-fat (HF) diets for 1 wk each. Although diet composition was fixed, total energy intake was unrestricted. Subjects had a higher energy intake on the HF (11,039 +/- 2700 kJ/d) than on the HC (10,672 +/- 2617 kJ/d) diet (P less than 0.05), but energy expenditure was not different between diets. On day 7 of the HC diet, carbohydrate (CHO) oxidation was significantly related to CHO intake with the slope of the regression line 0.99, suggesting that overall CHO balance was near zero. However, the slope of the regression line was greater for obese than for lean subjects. On day 7 of the HF diet, fat oxidation was significantly related to fat intake but the slope of the line was 0.50, suggesting that overall fat balance was positive. However, this relationship was due entirely to lean subjects, with obese subjects showing no relationship between fat intake and oxidation.