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.     

Thermogenesis induced by five different intravenous glucose/insulin infusions in healthy young men

The thermogenic response induced by glucose/insulin administered intravenously was examined in 22 healthy male volunteers using indirect calorimetry in combination with the euglycaemic insulin clamp technique. Five increasing steady state levels of insulinaemia (62 muU/ml to 1132 muU/ml) were achieved by means of continuous infusions of insulin at 5 rates ranging from 0.5 mU/kg.min to 10 mU/kg.min. Euglycaemia was maintained at each insulin level by infusing glucose at different rates ranging from steady state values of 0.41 g/min to 0.77 g/min. These glucose/insulin infusions resulted in a significant net rise in resting energy expenditure from 0.33 kJ/min to 0.94 kJ/min over preinfusion baseline values for the lowest and the highest doses respectively. There was a highly significant relationship (r = 0.93, p<0.001, n = 42) between the amount of glucose infused and the net increase in energy expenditure over preinfusion baseline values. Intravenous glucose induced thermogenesis (GIT(iv)) was calculated as incremental values of energy expenditure related to step changes in glucose infusion rates. GIT(iv) was found to be approximately 5.5% a physiological plasma insulin levels (i.e. below 200 muU/ml) whereas at supraphysiological levels (i.e.>400 muU/ml) GIT(iv) was increased up to 8%. It was concluded that: 1. the magnitude of the GIT(iv) at physiological insulinaemia was similar to that found by other investigators who have administered glucose per os; 2. the elevated thermogenesis observed at high doses of glucose/insulin infusion is consistent with recent clinical findings showing a markedly increased energy expenditure in patients supported by large quantities of intravenous glucose (TPN).     

Thermogenesis in men and women induced by fructose vs glucose added to a meal

Energy expenditure (EE) was measured by indirect calorimetry in 20 subjects (10 men and 10 women) for 30 min before and 6 h after the ingestion of a mixed meal containing 20% protein, 33% fat, and either 75 g glucose or 75 g fructose as carbohydrate source (47%). Diet-induced thermogenesis (DIT) and the rate of carbohydrate oxidation were significantly greater with fructose (12.4 +/- 0.6% and 54.8 +/- 2.1 g/6 h, respectively) than with glucose (10.7 +/- 0.7%, p less than 0.01, and 48.3 +/- 2.4 g/6 h, p less than 0.01, respectively). The DIT of male (12.1 +/- 1% and 13.9 +/- 0.8% with glucose and fructose, respectively) was greater than that of female subjects (9.2 +/- 0.7%, p less than 0.05, and 11.0 +/- 0.7%, p less than 0.05, respectively). In contrast to the glucose meal, negligible changes in plasma levels of glucose and insulin were observed with the fructose meal but plasma levels of lactate increased more with fructose than with glucose (peak values: 3.3 +/- 0.6 vs 1.5 +/- 0.1 mmol/L, respectively). When fructose provides the only carbohydrate source of a mixed meal, it induces a larger increase in carbohydrate oxidation and thermogenesis than when glucose is the carbohydrate source.     

Effect of prior exercise on postprandial triglycerides in overweight young women after ingesting a high-carbohydrate meal

To examine the effect of prior exercise on the postprandial lipid response to a high-carbohydrate meal in normal-weight (NW=BMI <25) and overweight (OW=BMI >or= 25) women (age 18-25), 10 NW and 10 OW participants completed 2 conditions separated by 1 month. In the morning, the day after control (CT=no exercise) or exercise conditions (EX=60 min cycling at 60% VO(2peak)), participants consumed a high-carbohydrate meal (80% CHO, 15% protein, 5% fat; 75 kJ/kg BM) followed by 6 hr of hourly blood sampling. Blood was analyzed for triglycerides (TG), blood glucose (BG), and insulin (IN). TG levels over the 6-hr period were lower in NW than OW (p= .021) and lower in EX than in CT (p= .006). Area under the curve (AUC) for TG was lower in NW than OW (p= .016) and EX than CT (p= .003). There were nonsignificant tendencies for reduced BG over time (p= .053) and AUC (p= .083), and IN AUC was lower in EX than in CT (p= .040) for both groups and lower in NW than in OW (p= .039). Prior exercise improved TG levels after a high-carbohydrate meal in both groups, and OW women demonstrated a greater postprandial lipemic response than NW regardless of condition. There were tendencies for improved glucose removal with prior exercise in NW vs. OW. Acute exercise can improve postprandial TG responses and might also improve postprandial BG and IN after a large meal in NW and OW young women.     

Body fat in lean and overweight women estimated by six methods

Body fat content of seven lean women (body mass index (BMI) 20.6 (SD 1.8) kg/m2) and seven overweight women (BMI 31.1 (SD 3.3) kg/m2) was estimated by six different methods: underwater weighing (UWW), body-water dilution (BWD), whole-body counting (40K), skinfold thickness (SFT), bioelectrical impedance (BEI) and magnetic resonance imaging (MRI). Using UWW as the reference method, the differences between percentage fat by each other method and the percentage fat by UWW were calculated for each subject. The mean difference was lowest for SFT and highest for BWD. MRI showed the lowest variability in individual results, and 40K the highest. 40K and BWD methods used in combination gave better agreement with UWW results than either 40K or BWD methods alone. There was a weak negative correlation between the difference from the UWW results and percentage fat in the SFT measurements, but not in the BWD, 40K, BEI or MRI measurements, suggesting that for these methods the assumptions involved produced no greater inaccuracy in the overweight women than in the lean women. In all subjects the BEI offered little improvement over the traditional SFT measurements. The agreement between MRI and UWW estimates in both lean and overweight women suggests that MRI may be a satisfactory substitute for the more established methods of body fat estimation in adult women.     

Effect of meal sequence on postprandial lipid, glucose and insulin responses in young men

OBJECTIVE: To investigate whether the postprandial changes in plasma triacylglycerol (TAG), nonesterified fatty acids (NEFA), glucose and insulin concentrations in young men were the same if an identical meal was fed at breakfast and lunch, and if the response to lunch was modified by consumption of breakfast. METHODS: In two trials (1 and 2) healthy subjects (age 22+/-1 y, body mass index 22+/-2 kg/m(2)) were fed the same mixed macronutrient meal at breakfast at 08:00 h and lunch at 14:00 h. In the third trial, no breakfast was fed and the overnight fast extended until lunch at 14:00 h. Addition of [1,1,1-(13)C]tripalmitin to one meal in each trial was used to distinguish between endogenous and meal-derived lipids. RESULTS: The postprandial changes in TAG, NEFA and glucose concentrations were similar in trials 1 and 2. The change in plasma total TAG concentration was about two fold less (P<0.05) after lunch compared to breakfast. Postprandial NEFA suppression was the same after breakfast and lunch. Glucose and insulin responses were significantly greater following lunch suggesting decreasing insulin sensitivity during the day. Consumption of breakfast did not alter the postprandial total TAG or NEFA responses after lunch. Measurement of [(13)C]palmitic acid concentration showed that handling of TAG and NEFA from the meal was the same after breakfast and lunch, and was not altered by consumption of breakfast. CONCLUSIONS: Overall, these data suggest that in young, healthy men regulation of plasma TAG from endogenous sources, principally VLDL, but not chylomicrons during the postprandial period leads to differences in the magnitude of lipaemic response when the same meal was consumed at breakfast or at lunch 6 h later.     

Effects of capsaicin-containing yellow curry sauce on sympathetic nervous system activity and diet-induced thermogenesis in lean and obese young women

The present study was designed to investigate the effect of capsaicin, a pungent component of red pepper, on the sympathetic nervous system (SNS) activity and energy metabolism in 16 age- and height-matched lean and obese young women. The sympatho-vagal activities were assessed by means of spectral analysis of heart rate variability (HRV) during the resting condition and after the meal (2,016 kJ) with capsaicin (3 mg). Energy expenditure was also measured under the two conditions. There was no significant difference in any of the parameters of the HRV between the obese and control groups at rest. After the capsaicin diet, however, the very low frequency component (0.007-0.035 Hz) associated with thermogenesis (315.8+/-78.0 vs. 814.8+/-211.7 ms2 x Hz(-1), p<0.05) as well as its responsiveness (delta changes: 14.6+/-104.4 vs. 369.2+/-121.7 ms2 x Hz(-1), p<0.05) were significantly lower in the obese than the control group. Energy expenditure was significantly increased in the control group after the meal (5,574.7+/-221.2 to 6,114.7+/-239.0 kJ day(-1); p<0.01), but no such significant thermogenic response was detected in the obese group despite nearly identical lean body mass of the control group. Our data indicate that regardless of the resting level of sympatho-vagal activities, the reduced sympathetic responsiveness to physiological perturbation such as a capsaicin diet, which may cause impaired diet-induced thermogenesis and further weight gain, could be an important etiological factor leading to obesity in young women.     

Gastric emptying rate,glycemic and appetite response to a liquid meal in lean and overweight males

The effect of body weight status on appetite, glycemic response and gastric emptying rate was investigated using a liquid meal. Lean and overweight males rated their subjective appetite with blood samples collected for measurement of glucose, biomarkers of appetite and gastric emptying rate for 3?h following consumption of the isocaloric test meal. Overweight participants had a higher rating on postprandial hunger (p?p?p?p?=?0.001). Postprandial plasma concentration of cholecystokinin-33 was lower (p?=?0.007) and total ghrelin was higher (p?=?0.012) in overweight participants. A delayed gastric emptying rate was observed in lean participants. There was no difference in postprandial glycemic response (p?=?0.189). These results suggest the postprandial appetite pattern was different between lean and overweight males when consuming an isocaloric meal. This may have implications for overweight individuals who attempt to lose weight through restricting food intake.     

Metabolic responses to high-fat or low-fat meals and association with sympathetic nervous system activity in healthy young men

The present study was designed to investigate the metabolic and sympathetic responses to a high-fat meal in humans. Fourteen young men (age: 23.6 +/- 0.5 y, BMI: 21.3 +/- 0.4 kg/m2) were examined for energy expenditure and fat oxidation measured by indirect calorimetry for 3.5 h after a high-fat (70%, energy from fat) or an isoenergetic low-fat (20% energy from fat) meal served in random order. The sympathetic nervous system (SNS) activity was assessed using power spectral analysis of heart rate variability (HRV). After the high-fat meal, increases in thermoregulatory SNS activity (very low-frequency component of HRV, 0.007-0.035 Hz, 577.4+/-45.9 vs. 432.0+/-49.3 ms2, p<0.05) and fat oxidation (21.0+/-5.3 vs. 13.3+/-4.3 g, p<0.001) were greater than those after the low-fat meal. However, thermic effects of the meal (TEM) were lower after the high-fat meal than after the low-fat meal (27.5+/-11.2 vs. 36.1+/-10.9 kcal, p<0.05). In conclusion, the high-fat meal can stimulate thermoregulatory SNS and lipolysis, but resulted in lower TEM, suggesting that a high proportion of dietary fat intake, even with a normal daily range of calories, may be a potent risk factor for further weight gain.     

Body fat distribution and insulin resistance: beyond obesity in nonalcoholic fatty liver disease among overweight men

OBJECTIVE: The aim of this study was to characterize the relationship between nonalcoholic fatty liver disease (NAFLD) and body fat distribution and insulin resistance in a sample of non-diabetic overweight men. SUBJECTS AND METHODS: We conducted a cross-sectional survey of 117 overweight men with NAFLD, as well as 117 controls, who were matched with regard to age and body mass index. None of the study subjects exhibited signs of alcohol abuse, hepatitis B or C, diabetes or fasting hyperglycemia, or hypertension. The diagnosis of NAFLD was based on dual findings of elevated alanine aminotransferase levels and sonographically-determined fatty liver. Body fat distribution was assessed via bioelectrical impedance. Insulin resistance was evaluated via homeostasis model assessment (HOMA-IR). RESULTS: The risk of developing NAFLD was found to be profoundly associated with elevated measurements of waist circumference, fat mass, percentage of body fat and abdominal fat, iron, triglycerides, apolipoprotein B, and results of HOMA-IR. Multivariate analysis revealed that NAFLD was significantly associated with elevated measurements of waist circumference, iron, apolipoprotein B, and HOMA-IR. CONCLUSIONS: Our study provides evidence for a profound and dose-dependent association of NAFLD with central adiposity, insulin resistance in overweight men lacking complications of metabolic syndrome. Overweight subjects with insulin resistance or central adiposity were at more risk of NAFLD than were those subjects with less insulin resistance or central adiposity, even those with a similar degree of obesity.     

Effects of olestra, a noncaloric fat substitute, on daily energy and fat intakes in lean men.

Nutrient and energy intakes, hunger, and fullness were examined after the replacement of 36, 20, or 0 g fat in breakfast with olestra, a noncaloric fat substitute. Twenty-four lean, nondieting men (aged 21-30 y) participated in a placebo-controlled, three-condition crossover design. Self-selected, ad libitum intakes at lunch and dinner were monitored in the laboratory. Evening snacks and breakfast the next day were assessed through food diaries. Visual-analog-scale ratings including hunger and fullness were collected throughout the test days. Single-meal olestra substitution produced a significant dose-related reduction in the amount and percentage of energy from fat consumed daily with a reciprocal increase in carbohydrate intake. Daily energy intakes were not significantly different nor did ratings of hunger and fullness vary systematically between conditions. Consumption of olestra can reduce fat intake and increase carbohydrate intake without affecting total daily energy intake or usual patterns of hunger and fullness.     

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.     

Relationships between insulin sensitivity and measures of body fat in asymptomatic men and women

OBJECTIVE: To assess whether measures of body fat by DXA scanning can improve prediction of insulin sensitivity (S(I)) beyond what is possible with traditional measures, such as BMI, waist circumference, and waist-to-hip ratio (WHR). RESEARCH METHODS AND PROCEDURES: Frequently sampled intravenous glucose tolerance tests were performed in 256 asymptomatic non-Hispanic white subjects from Rochester, MN (age 19-60 years; 123 men and 133 women) to determine the S(I) index by Bergman's minimal model technique. Height, weight, and waist and hip circumferences were measured for calculation of BMI and WHR; DXA was used to determine fat in the head, upper body, abdomen, and lower body. Linear regression was used to assess their relationships with S(I) after sex stratification and adjustment for age. RESULTS: After controlling for age, increases in traditional and DXA measures of fat were consistently associated with smaller declines in S(I) among women than among men. In men, after controlling for age, all of the predictive information of S(I) was provided by waist circumference (additional R2 = 0.39, p < 0.001); none of the DXA measures improved the ability to predict S(I). In women, after adjustment for age, BMI, and WHR, the only DXA measure that improved the prediction of S(I) was percentage head fat (additional R2 = 0.03, p < 0.001). DISCUSSION: Equivalent increases in most measures of body fat had lesser impact on S(I) in women than in men. In both sexes, the predictive information provided by DXA measures is approximately equal to, but not additive to, that provided by simpler, traditional measures.     

Effects of meal consumption on whole body leucine and alanine kinetics in young adult men

The effects of meal consumption on plasma leucine and alanine kinetics were studied using a simultaneous, primed, continuous infusion of L-[1-13C]leucine and L-[3,3,3-2H3]alanine in four healthy, young, adult male subjects. The study included an evaluation of the effect of sampling site on plasma amino acid kinetics, with blood being drawn simultaneously from an antecubital and dorsal heated hand vein. In comparison with the postabsorptive state, the ingestion of small hourly meals resulted in a 35% increase in plasma leucine flux and a 77% increase in leucine oxidation. Calculated entry of leucine into the plasma compartment from endogenous sources decreased by 65%. Plasma alanine flux more than doubled, indicating a significant enhancement in de novo alanine synthesis. 13C enrichment of leucine in venous and arterialized plasma did not differ significantly, but alanine flux calculated from isotopic measurement in venous plasma was substantially greater than that based on analysis of arterialized blood plasma.     

Thermic effect of feeding carbohydrate, fat, protein and mixed meal in lean and obese subjects

The thermic effect of 1.67 MJ (400 kcal) of carbohydrate (glucose), fat, protein and mixed meal were examined in 11 lean and 11 obese subjects by indirect calorimetry. The changes in metabolic rate in response over 90 min period (30-120 min after the meal) to the different meals were compared with that seen after a similar volume of low calorie drink. The thermic effects of glucose and protein were not significantly different between lean and obese subjects. Obese subjects showed very little increase in metabolic rate following ingestion of fat (-0.9 +/- 2.0%, mean +/- SEM) and this was significantly different from that seen in lean subjects (14.4 +/- 3.4%). The thermogenic response to mixed meal was also significantly lower in obese subjects when expressed as percentage change (12.9 +/- 2.3% compared to 25.0 +/- 4.8%). There was no evidence for delay in gastric emptying times for glucose and fatty meal in the six obese subjects in whom these were measured. We conclude that obese subjects show a reduced thermogenic response to fat.     

Comparison of high-fat and high-carbohydrate foods in a meal or snack on short-term fat and energy intakes in obese women

The present study aimed to compare the action of high-fat and high-carbohydrate (CHO) foods on meal size (satiation) and post-meal satiety in obese women. A within-subjects design was used; each participant received all four nutritional challenges. Fifteen healthy obese women (age 21-56 years, BMI 35-48 kg/m2) participated; thirteen completed all four test days. On two test days, participants were exposed to a nutritional challenge comprising an ad libitum high-fat or high-CHO lunch. On the other two test days they were exposed to a challenge comprising an ad libitum sweet high-fat or high-CHO mid-afternoon snack. Energy and macronutrient intakes were measured at each eating episode. Visual analogue rating scales were completed periodically to record subjective feelings of appetite. When offered a high-CHO selection of foods at lunch and mid-afternoon participants consumed less energy than when offered a high-fat selection. However, post-meal satiety was similar. Total test-day energy intake was significantly higher when high-fat foods were consumed at lunch, but not as a snack. Consumption of high-fat foods at a lunch and snack increased the amount of fat consumed over the whole test day. In conclusion, energy intake of an eating episode was influenced by nutrient composition in this group of obese women. Consumption of high-fat foods at lunch or as a snack led to overconsumption relative to high-CHO foods. However, high-fat foods at meals may have greater potential to influence daily intake than at snacks, probably because meals are larger eating episodes and therefore give greater opportunity to overconsume.     

Substitution of saturated with monounsaturated fat in a 4-week diet affects body weight and composition of overweight and obese men

A randomised crossover study of eight overweight or obese men (aged 24-49 years, BMI 25.5-31.3 kg/m(2)), who followed two diets for 4 weeks each, was performed to determine whether substitution of saturated fat with monounsaturated fat affects body weight and composition. Subjects were provided with all food and beverages as modules (selected ad libitum) of constant macronutrient composition, but differing energy content. The % total energy from saturated fat, monounsaturated fat and polyunsaturated fat was 24, 13 and 3 % respectively on the saturated fatty acid (SFA)-rich diet and 11, 22 and 7 % respectively on the monounsaturated fatty acid (MUFA)-rich diet. MUFA accounted for about 80 % of the unsaturated fats consumed on both diets. Body composition, blood pressure, energy expenditure (resting and postprandial metabolic rates, substrate oxidation rate, physical activity), serum lipids, the fatty acid profile of serum cholesteryl esters and plasma glucose and insulin concentrations were measured before and after each diet period. Significant (P< or =0.05) differences in total cholesterol and the fatty acid composition of serum cholesteryl esters provided evidence of dietary adherence. The men had a lower weight (-2.1 (SE 0.4) kg, P=0.0015) and fat mass (-2.6 (SE 0.6) kg, P=0.0034) at the end of the MUFA-rich diet as compared with values at the end of the SFA-rich diet. No significant differences were detected in energy or fat intake, energy expenditure, substrate oxidation rates or self-reported physical activity. Substituting dietary saturated with unsaturated fat, predominantly MUFA, can induce a small but significant loss of body weight and fat mass without a significant change in total energy or fat intake.     

Differences in the relationship between BMI and percentage body fat between Japanese and Australian-Caucasian young men

This cross-sectional study aimed to determine ethnic and environmental influences on the relationship between BMI and percentage body fat, using a sample of 144 Japanese and 140 Australian-Caucasian men living in Australia, and eighty-eight Japanese men living in Japan. Body composition was assessed by anthropometry using standard international methods (International Society for the Advancement of Kinanthropometry protocol). Body density was predicted using Durnin and Womersley's (1974) equation, and percentage body fat was calculated from Siri's (1961) equation. Significant (P<0.05) ethnic differences in stature, body mass and BMI were observed between Japanese and Australian men, but no ethnic differences were observed in their percentage body fat and height-corrected sum of skinfold thicknesses. No differences were found in the BMI-percentage body fat relationship between the Japanese subjects living in Australia and in Japan. Significant (P<0.05) ethnic differences in the BMI-percentage body fat relationship observed from a comparison between pooled Japanese men (aged 18-40 years, BMI range 16.6-32.8 kg/m2) and Australians (aged 18-39 years, BMI range 16.1-31.4 kg/m2) suggest that Japanese men are likely to have a greater percentage body fat than Australian men at any given BMI value. From the analyses, the Japanese men were estimated to have an equivalent amount of body fat to the Australian men at BMI values that were about 1.5 units lower than those of the Australians (23.5 kg/m2 and 28.2 kg/m2, respectively). It was concluded that Japanese men have greater body fat deposition than Australian-Caucasians at the same BMI value. Japanese men may therefore require lower BMI cut-off points to identify obese individuals compared with Australian-Caucasian men.