Glycemic index of a meal fed before exercise alters substrate use and glucose flux in exercising horses.

In a randomized, balanced, crossover study each of six fit, adult horses ran on a treadmill at 50% of maximal rate of oxygen consumption for 60 min after being denied access to food for 18 h and then 1) fed corn (51.4 kJ/kg digestible energy), or 2) fed an isocaloric amount of alfalfa 2-3 h before exercise, or 3) not fed before exercise. Feeding corn, compared with fasting, resulted in higher plasma glucose and serum insulin and lower serum nonesterified fatty acid concentrations before exercise (P < 0.05) and in lower plasma glucose, serum glycerol, and serum nonesterified fatty acid concentrations and higher skeletal muscle utilization of blood-borne glucose during exercise (P < 0.05). Feeding corn, compared with feeding alfalfa, resulted in higher carbohydrate oxidation and lower lipid oxidation during exercise (P < 0.05). Feeding a soluble carbohydrate-rich meal (corn) to horses before exercise results in increased muscle utilization of blood-borne glucose and carbohydrate oxidation and in decreased lipid oxidation compared with a meal of insoluble carbohydrate (alfalfa) or not feeding. Carbohydrate feedings did not produce a sparing of muscle glycogen compared with fasting.     

Aerobic training improves exercise-induced lipolysis in SCAT and lipid utilization in overweight men

The aim of this study was to investigate whether endurance training improves lipid mobilization and oxidation in overweight subjects. Eleven young men (25.6 +/- 1.4 yr and body mass index 27.7 +/- 0.2) performed a 4-mo training program consisting of practicing aerobic exercise 5 days/wk. Before and after the training period, lipid oxidation was explored during a 60-min exercise at 50% of peak O2 consumption by use of indirect calorimetry. Lipid mobilization and antilipolytic alpha2-adrenoceptor effect were also studied using the microdialysis method in abdominal subcutaneous adipose tissue (SCAT). After training, plasma nonesterified fatty acid (NEFA) levels, at rest and during exercise, were significantly lower than before (P < 0.001). Lipolysis in SCAT was significantly higher after than before training. An antilipolytic alpha2-adrenoceptor effect in SCAT was underlined during exercise before training and disappeared after. The respiratory exchange ratio was lower after training, i.e., the percentage of lipid oxidation was higher only at rest. The amount of lipid oxidized was higher after training, at rest, and during exercise. Although exercise power was higher after training, the relative intensity was equivalent, as suggested by a similar increase in plasma catecholamine concentrations before and after training. In conclusion, 4-mo training in overweight men improved lipid mobilization through a decrease of antilipolytic alpha2-adrenoceptor effect in SCAT and lipid oxidation during moderate exercise. Training induced a decrease of blood NEFA, predicting better prevention of obesity.     

Substrate usage during prolonged exercise following a preexercise meal

The effect of a high-carbohydrate meal 4 h before 105 min of exercise at 70% of maximal O2 uptake was determined in seven endurance-trained cyclists and compared with exercise following a 16-h fast. The preexercise meal produced a transient elevation of plasma insulin and blood glucose, which returned to fasting basal levels prior to the initiation of exercise. The meal also resulted in a 42% elevation (P less than 0.05) of glycogen within the vastus lateralis at the beginning of exercise. The 1st h of exercise when subjects were fed was characterized by a 13-25% decline (P less than 0.05) in blood glucose concentration, a suppression of the normal increase in plasma free fatty acids and blood glycerol, and a 45% (P less than 0.05) greater rate of carbohydrate oxidation compared with exercise when subjects were fasted. After 105 min of exercise, there were no significant differences when subjects were fed or fasted regarding blood glucose levels, rate of carbohydrate oxidation, or muscle glycogen concentration. The greater muscle glycogen utilization (97 +/- 18 vs. 64 +/- 8 mmol glucosyl units X kg-1; P less than 0.05) and carbohydrate oxidation when subjects were fed appeared to be derived from the glycogen synthesized following the meal. These results indicate that preexercise feedings alter substrate availability despite a return of plasma insulin to fasting levels prior to exercise and that these effects persist until the 2nd h of exercise.     

Acute exposure to long-chain fatty acids impairs {alpha}2-adrenergic receptor-mediated antilipolysis in human adipose tissue

The acute in vitro and in vivo effects of long-chain fatty acids (LCFAs) on the regulation of adrenergic lipolysis were investigated in human adipose tissue. The effect of a 2 h incubation, without or with LCFA (200 mumol/l), on basal and hormonally induced lipolysis was tested in vitro on isolated fat cells. The lipolytic response to epinephrine was enhanced by suppression of the antilipolytic alpha(2)-adrenergic effect. Then, healthy lean and obese male subjects performed a 45 min exercise bout at 50% of their heart rate reserve either after an overnight fast or 3 h after a high-fat meal (HFM: 95% fat, 5% carbohydrates). Subcutaneous adipose tissue lipolysis was measured by microdialysis in the presence or absence of an alpha-antagonist (phentolamine). In vivo, a HFM increased plasma levels of nonesterified fatty acids in lean and obese subjects. In both groups, the HFM did not alter hormonal responses to exercise. Under fasting conditions, the alpha(2)-adrenergic antilipolytic effect was more pronounced in obese than in lean subjects. The HFM totally suppressed the alpha(2)-adrenergic antilipolytic effect in lean and obese subjects during exercise. LCFAs per se, in vitro as well as in vivo, suppress alpha(2)-adrenergic-mediated antilipolysis in adipose tissue. LCFA-mediated suppression of antilipolytic pathways represents another mechanism whereby a high fat content in the diet might increase adipose tissue lipolysis.     

Lifestyle Intervention and Fatty Acid Metabolism in Glucose‐Intolerant Subjects

Objective: Free fatty acid (FFA) oxidation is reduced in subjects with type 2 diabetes mellitus and impaired glucose tolerance (IGT). Weight reduction does not improve these impairments. Because exercise training is known to increase fatty acid (FA) oxidation, we investigated whether a combined diet and physical activity intervention program can improve FA oxidation in subjects with IGT. Research Methods and Procedures: Sixteen subjects with IGT were studied before and after 1 year of a lifestyle intervention program [nine intervention (INT) subjects, seven controls (CON)]. INT subjects received regular (i.e., every 3 months) dietary advice and were stimulated to increase their level of physical activity. Glucose tolerance, anthropometric characteristics, and substrate use at rest and during exercise were evaluated before and after 1 year. Substrate oxidation was measured at rest and during moderate intensity exercise using indirect calorimetry in combination with stable isotope infusion ([U‐¹³C]palmitate and [6, 6‐²H₂‐]glucose). Results: After 1 year, no differences were seen in substrate use at rest. During exercise, total fat and plasma FFA oxidation were slightly increased in the INT group and decreased in the CON group, with the change being significantly different (change after 1 year: INT, +2.0 ± 1.4 and +1.9 ± 0.9 μmol/kg per minute; CON, ?3.5 ± 1.6 and ?1.8 ± 0.5 μmol/kg per minute for total and plasma FFA, respectively; p < 0.05). Discussion: A combined diet and physical activity intervention program can prevent further deterioration of impaired FA oxidation during exercise in subjects with IGT.     

Leptin, superoxide dismutase, and weight loss: initial leptin predicts weight loss

Objective: Our goal was to study how plasma leptin concentration, superoxide dismutase (SOD) activity, and weight loss are related in obese adults. Research Methods and Procedures: Serum leptin concentration, SOD activities, general biochemical data, and body composition measurements were obtained for 62 overweight and obese subjects before and after an 8‐week body weight reduction (BWR) regimen. The subjects were on dietary control, performed moderate aerobic and strength training exercises, and attended educational lectures. Results: The measurement results indicated that the following criteria were significantly reduced: body weight [84.4 ± 17.0 vs. 79.3 ± 16.1 (standard error) kg, p < 0.001]; BMI (31.5 ± 4.3 vs. 29.4 ± 4.2 kg/m², p < 0.001), and fat mass (33.3 ± 10.0 vs. 29.8 ± 10.4 kg, p < 0.001). Plasma leptin levels also significantly decreased from 31.5 ± 17.6 to 26.5 ± 17.2 ng/mL (p < 0.001). Additionally, SOD activity was significantly increased from 261.4 ± 66.0 to 302.7 ± 30.9 U/mL (p < 0.001). Based on linear regression analysis results, a 3.78‐ to 8.13‐kg reduction in weight can be expected after the 8‐week BWR regimen when initial leptin concentration was 5 to 30 ng/mL. Discussion: We found that an 8‐week exercise and diet program was effective in reducing weight and fat mass and, notably, had further beneficial effects on leptin resistance and SOD activity. Additionally, this study demonstrated that initial plasma leptin concentration may be used as a predictor for weight loss outcome.     

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% VO_2peak 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.     

Lipid oxidation according to intensity and exercise duration in overweight men and women

Objective: Our objective was to compare the effect of different exercise intensities on lipid oxidation in overweight men and women. Research Methods and Procedures: Nine young, healthy, overweight men and women were studied (age, 31.4 ± 2.3 and 26.7 ± 2.1 years; BMI, 27.9 ± 0.4 and 27.2 ± 0.5; for men and women, respectively). On one study day, the subjects first performed 30 minutes of cycling exercise at 30% of their maximal oxygen uptake (Vo _2max; E1 session), followed by 30 minutes of exercise at 50% Vo _2max (E2 session). On a second study day, a similar E1 session was followed by 30 minutes of exercise at 70% Vo _2max (E3 session). From the gas exchange measurements, the respiratory exchange ratio (RER) and the fat oxidation rate (FOR) were calculated. Plasma concentrations of glycerol and non‐esterified fatty acids (NEFAs) were assayed. Results: RER was significantly lower for women during only the E1 session. For both sexes, RER decreased over time during the E2 and E3 sessions. During the E1 session, the FOR per kilogram of lean mass (LM) was higher among women, and it did not change over time despite an increase in plasma NEFAs. FOR per kilogram of LM was higher during the E2 exercise for both sexes. During E2 and E3 sessions, as the exercise time was prolonged, the FOR/kg LM increased simultaneously with the increase in the plasma glycerol. Discussion: Lipid oxidation during exercise is optimized for moderate and lengthy exercise. The enhancement of lipid oxidation occurring over time during moderate‐ and high‐intensity exercises could be, in part, linked to the improvement of lipid mobilization. This fact is discussed to shed light on exercise modalities as a tool for the management of overweight.     

Effects of Dinner Composition on Postprandial Macronutrient Oxidation in Prepubertal Girls

Objective: To see whether a fat‐rich (50%) evening meal promoted fat oxidation and a different spontaneous food intake on the following day at breakfast than a meal with a lower fat content (20%) in 10 prepubertal obese girls. Research Methods and Procedures: The postabsorptive and postprandial (10.5 hours) energy expenditure after a low‐fat (LF) (20% fat, 68% carbohydrate, 12% protein) and an isocaloric (2.1 MJ) and isoproteic high‐fat (HF; 50% fat, 38% carbohydrate, 12% protein) meal were measured by in direct calorimetry. Results: Fat oxidation was not significantly different after the two meals [LF, 31 ± 9 vs. HF, 35 ± 9 g/10.5 hours, p = not significant (NS)]. The girls oxidized 1.8 ± 0.9 times more fat than that ingested (11.1 grams) with the LF meal vs. 0.3 ± 0.3 times more fat than that ingested (27.1 grams) with the HF meal (p < 0.001). Carbohydrate oxidation was significantly higher after an LF than an HF meal (39 ± 12 vs. 29 ± 9 g/10.5 hours, p < 0, 05). At breakfast, the girls spontaneously ingested a similar amount of energy (1.5 ± 0.7 vs. 1.5 ± 0.6 MJ, p = NS) and macronutrient proportions (fat, 23% vs. 26%, p = NS; protein, 9% vs. 10%; carbohydrate, 68% vs. 64%,) independently of their having eaten an HF or an LF dinner. Discussion: An HF dinner did not stimulate fat oxidation, and no compensatory effect in spontaneous food intake was observed during breakfast the following morning. Cumulated total fat oxidation after dinner was higher than total fat ingested at dinner, but a much larger negative fat balance was observed after the LF meal. Spontaneous energy and nutrient intakes at breakfast were similar after LF and HF isocaloric, isoproteic dinners. This study points out the lack of sensitivity of short‐term fat balance to subsequently readjust fat intake and emphasizes the importance of an LF meal to avoid transient positive fat imbalance.     

Pre-meal water consumption reduces meal energy intake in older but not younger subjects

Objective: To determine whether the consumption of water 30 minutes before an ad libitum meal reduces meal energy intake in young and older adults. Research Methods and Procedures: Healthy, non‐obese young (n = 29; age, 21 to 35 years) and older (n = 21; age, 60 to 80 years) individuals were provided with an ad libitum lunch meal on two occasions. Thirty minutes before the lunch meals, subjects were given either a water preload (WP: 375 mL, women; 500 mL, men) or no preload (NP). Energy intake at the two lunch meals was measured. Visual analog scales were used to assess changes in hunger, fullness, and thirst during the meal studies. Results: There was no significant difference in meal energy intake between conditions in the young subjects (892 + 51 vs. 913 ± 54 kcal for NP and WP, respectively; p = 0.65). However, meal energy intake after the WP was significantly reduced relative to the NP condition in the older subjects (682 + 53 vs. 624 ± 56 kcal for NP and WP, respectively; p = 0.02). This effect was caused primarily by the reduction in meal energy intake after water consumption in older men. Hunger ratings were lower and fullness ratings were higher in older compared with younger adults (p < 0.01). Fullness ratings were higher in the WP condition compared with the NP condition for all subjects (p = 0.01). No age differences in thirst were detected during the test meals. Discussion: Under acute test meal conditions, pre‐meal water consumption reduces meal energy intake in older but not younger adults. Because older adults are at increased risk for overweight and obesity, intervention studies are needed to determine whether pre‐meal water consumption is an effective long‐term weight management strategy for the aging population.     

Muscle GSH-Px activity after prolonged exercise,training, and selenium supplementation

A double-blind study of the effects of supplementing with selenium vs. placebo on the physiological responses to acute and chronic exercise was conducted in 24 healthy, nonsmoking males, mean age 22.9±2.1 yr, randomly divided into two groups of 12 (Pla/Sel). After a controlled period in the absence of training, all subjects were put on an individualized endurance training program with the same rules of progression and overload (3 sessions/wk×10 wk). Supplementation, either real (240 μg of organic selenium/d in Sel group) or imaginary (Pla group) was administered during the same period. In each of the conditions Pre- and Post- (training ± sel supplementation), muscle, plasma, and systemic parameters were determined before (BF) and after (AF) acute exercise, involving the repetition of muscle work cycles separated by 5-min recovery periods, combining 20 min at 65% and a maximal duration of 100% VO₂ max of running on a treadmill, leading the subjects to exhaustion between 2 h 40 min and 3 h 30 min. Changes in parameters as a function of three independent variables:

1. Acute exercise (E);
2. Chronic exercise (T); and
3. Selenium supplementing (S)

were tested with ANOVA and the Student\rsst-test on paired series. Among the variables examined, muscle glutathione peroxidase (GPx) presented a remarkable behavior. Enzymatic activity:

1. Decreased significantly (p<0.05,n=24) between the beginning and the end of acute exercise: 29.6±12 vs. 20.8±8.1 IU·g protein^?1 in Pre conditions;
2. Remained at the same level in resting conditions between the beginning and end of training (from Pre to Post) regardless of the group: 33.5±10.8 vs. 32.3±19.8 and 25.7±12.4 vs. 23.5±10.2 IU·g protein^?1 in Pla and Sel subjects, respectively; and
3. Increased from 23.5±10.2 to 37.3±28.5 (P=0.057) during acute exercise in Post-conditions (after training) in supplemented subjects (Sel group).

The situation was as if acute exercise played the role of allosteric stimulator of the GPx reaction in muscle.     

Insulin Resistance in Nondiabetic Morbidly Obese Patients: Effect of Bariatric Surgery

Objective: To evaluate insulin action on substrate use and insulinemia in nondiabetic class III obese patients before and after weight loss induced by bariatric surgery. Research Methods and Procedures: Thirteen obese patients (four men/nine women; BMI = 56.3 ± 2.7 kg/m²) and 13 lean subjects (five men/eight women; BMI = 22.4 ± 0.5 kg/m²) underwent euglycemic clamp, oral glucose tolerance test, and indirect calorimetry. The study was carried out before (Study I) and after (～40% relative to initial body weight; Study II) weight loss induced by Roux‐en‐Y Gastric bypass with silastic ring surgery. Results: The obese patients were insulin resistant (whole‐body glucose use = 19.7 ± 1.5 vs. 51.5 ± 2.4 μmol/min per kilogram fat‐free mass, p < 0.0001) and hyperinsulinemic in the fasting state (332 ± 86 vs. 85 ± 5 pM, p < 0.0001) and during the oral glucose tolerance test compared with the lean subjects. Fasting plasma insulin normalized after weight loss, whereas whole‐body glucose use increased (35.5 ± 3.7 μmol/min per kilogram fat‐free mass, p < 0.05 vs. Study I). The higher insulin clearance of obese did not change during the follow‐up period. Insulin‐induced glucose oxidation and nonoxidative glucose disposal were lower in the obese compared with the lean group (all p < 0.05). In Study II, the former increased slightly, whereas nonoxidative glucose disposal reached values similar to those of the control group. Fasting lipid oxidation was higher in the obese than in the control group and did not change significantly in Study II. The insulin effect on lipid oxidation was slightly improved (p = 0.01 vs. Study I). Discussion: The rapid weight loss after surgery in obese class III patients normalized insulinemia and improved insulin sensitivity almost entirely due to glucose storage, whereas fasting lipid oxidation remained high.     

High‐density Lipoprotein Apolipoprotein A‐I Kinetics in Obesity

Objective: Low plasma concentrations of high‐density lipoprotein (HDL)‐cholesterol and apolipoprotein A‐I (apoA‐I) are independent predictors of coronary artery disease and are often associated with obesity and the metabolic syndrome. However, the underlying kinetic determinants of HDL metabolism are not well understood. Research Methods and Procedures: We pooled data from 13 stable isotope studies to investigate the kinetic determinants of apoA‐I concentrations in lean and overweight—obese individuals. We also examined the associations of HDL kinetics with age, sex, BMI, fasting plasma glucose, fasting insulin, Homeostasis Model Assessment score, and concentrations of apoA‐I, triglycerides, HDL‐cholesterol and low‐density lipoprotein‐cholesterol. Results: Compared with lean individuals, overweight—obese individuals had significantly higher HDL apoA‐I fractional catabolic rate (0.21 ± 0.01 vs. 0.33 ± 0.01 pools/d; p < 0.001) and production rate (PR; 11.3 ± 4.4 vs. 15.8 ± 2.77 mg/kg per day; p = 0.001). In the lean group, HDL apoA‐I PR was significantly associated with apoA‐I concentration (r = 0.455, p = 0.004), whereas in the overweight—obese group, both HDL apoA‐I fractional catabolic rate (r = ?0.396, p = 0.050) and HDL apoA‐I PR (r = 0.399, p = 0.048) were significantly associated with apoA‐I concentration. After adjustment for fasting insulin or Homeostasis Model Assessment score, HDL apoA‐I PR was an independent predictor of apoA‐I concentration. Discussion: In overweight—obese subjects, hypercatabolism of apoA‐I is paralleled by an increased production of apoA‐I, with HDL apoA‐I PR being the stronger determinant of apoA‐I concentration. This could have therapeutic implications for the management of dyslipidemia in individuals with low plasma HDL‐cholesterol.     

Metabolic and performance responses during endurance exercise after high-fat and high-carbohydrate meals

We studied the effects of preexercise mealcomposition on metabolic and performance-related variables duringendurance exercise. Eight well-trained cyclists (maximal oxygen uptake65.0 to 83.5 ml · kg¹ · min¹)were studied on three occasions after an overnight fast. They weregiven isoenergetic meals containing carbohydrate (CHO), protein (P),and fat (F) in the following amounts (g/70 kg body wt):high-carbohydrate meal, 215 CHO, 26 P, 3 F; high-fat meal, 50 CHO, 14 P, 80 F. On the third occasion subjects were studied after an overnightfast. Four hours after consumption of the meal, subjects startedexercise for 90 min at 70% of their maximal oxygen uptake, followed by a 10-km time trial. The high-carbohydrate meal compared with the high-fat meal resulted in significant decreases(P < 0.05) in blood glucose, plasmanonesterified fatty acids, plasma glycerol, plasmachylomicron-triacylglycerol, and plasma 3-hydroxybutyrate concentrations during exercise. This was accompanied by anincrease in plasma insulin (P < 0.01 vs. no meal), plasma epinephrine, and plasma growth hormoneconcentrations (each P < 0.05 vs.either of the other conditions) during exercise. Despite these large differences in substrate and hormone concentrations in plasma, substrate oxidation during the 90-min exercise period was similar inthe three trials, and there were no differences in performance on thetime trial. These results suggest that, although the availability offatty acids and other substrates in plasma can be markedly altered bydietary means, the pattern of substrate oxidation during enduranceexercise is remarkably resistant to alteration.

     

Regular Aerobic Exercise,Without Weight Loss,Improves Endothelium‐dependent Vasodilation in Overweight and Obese Adults

Lifestyle modification in the form of weight reduction by caloric restriction alone or in combination with regular aerobic exercise significantly improves endothelium‐dependent vasodilation in overweight and obese adults. We determined whether regular aerobic exercise, independent of weight loss, improves endothelium‐dependent vasodilation in overweight and obese adults. Twenty overweight and obese adults (age 53 ± 1 years; BMI: 30.2 ± 0.8 kg/m²) were studied before and after a 3‐month aerobic exercise training intervention. Forearm blood flow (FBF) responses were determined (via plethysmography) in response to intra‐arterial infusion of acetylcholine and sodium nitroprusside. There were no changes in body mass or composition with the intervention. FBF responses to acetylcholine were ～35% higher (P < 0.01) after (4.1 ± 0.9 to 14.7 ± 4.3 ml/100 ml tissue/min) compared with before (4.2 ± 0.8 to 11.0 ± 3 ml/100 ml tissue/min) exercise training. FBF responses to sodium nitroprusside were unchanged. These results indicate that regular aerobic exercise improves endothelium‐dependent vasodilation in overweight and obese adults, independent of changes in body mass or composition.     

Circadian Eating and Sleeping Patterns in the Night Eating Syndrome

Objective: To compare the eating and sleep‐wake patterns of persons with the night eating syndrome (NES) with those of matched control subjects. Research Methods and Procedures: Forty‐six overweight/obese NES subjects (mean age 43.3 ± 9.8 years; 32 women) and 43 similar controls (mean age 39.0 ± 11.0 years; 28 women) wore wrist actigraphs for 7 days and completed sleep and food diaries at home. Results: There was no difference between the total energy intake of the NES and the control subjects, but the pattern of energy intake differed greatly. Relative to control subjects, the temporal pattern of food intake of night eaters was delayed. Food intake after the evening meal, as a proportion of the 24‐hour intake, was more than 3‐fold greater in NES subjects than in controls (34.6 ± 10.1% vs. 10.0 ± 6.9%, p = 0.001). NES subjects had sleep onset, offset, and total sleep duration times comparable with those of controls. NES subjects reported more nocturnal awakenings than did controls (1.5 ± 1.0 per night vs. 0.5 ± 0.5; p < 0.001), and their actigraphically monitored arousals occurred earlier during sleep (at 128 minutes after sleep onset vs. 193 minutes, p = 0.01). NES subjects consumed food on 74% of the awakenings vs. 0% for the controls. Discussion: The pattern of cumulative energy intake of the night eaters suggests a phase delay in energy consumption relative to sleep‐wake times. NES may involve a dissociation of the circadian control of eating relative to sleep.     

Low Plasma Leptin Concentration and Low Rates of Fat Oxidation in Weight‐Stable Post‐Obese Subjects

Objective: A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post‐obese adults (2 males and 6 females; 48.9 ± 12.2 years; body mass index [BMI]: 24.5 ± 1.0 kg/m²; body fat 33 ± 5%; mean ± SD) who lost 27.1 ± 21.3 kg (16 to 79 kg) and had maintained this weight loss for ≥2 months (2 to 9 months) to eight age‐ and BMI‐matched control never‐obese subjects (1 male and 7 females; 49.1 ± 5.2 years; BMI 24.4 ± 1.0 kg/m²; body fat 33 ± 7%). Research Methods and Procedures: Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10‐hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48‐hour period in free living conditions. Results: After adjustment for fat mass and fat‐free mass, post‐obese subjects had, compared with controls, similar levels of physical activity (4185 ± 205 vs. 4295 ± 204 counts) and similar RMR (1383 ± 268 vs. 1430 ± 104 kcal/day) but higher RQ (0.86 ± 0.04 vs. 0.81 ± 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat‐free mass, was lower in post‐obese than in control subjects (4.5 ± 2.1 vs. 11.6 ± 7.9 ng/mL, p < 0.05). Discussion: The low fat oxidation and low plasma leptin concentrations observed in post‐obese individuals may, in part, explain their propensity to relapse.     

Effects of a Low Carbohydrate Weight Loss Diet on Exercise Capacity and Tolerance in Obese Subjects

Dietary restriction and increased physical activity are recommended for obesity treatment. Very low carbohydrate diets are used to promote weight loss, but their effects on physical function and exercise tolerance in overweight and obese individuals are largely unknown. The aim of this study was to compare the effects of a very low carbohydrate, high fat (LC) diet with a conventional high carbohydrate, low fat (HC) diet on aerobic capacity, fuel utilization during submaximal exercise, perceived exercise effort (RPE) and muscle strength. Sixty subjects (age: 49.2 ± 1.2 years; BMI: 33.6 ± 0.5 kg/m²) were randomly assigned to an energy restricted (～6–7 MJ, 30% deficit), planned isocaloric LC or HC for 8 weeks. At baseline and week 8, subjects performed incremental treadmill exercise to exhaustion and handgrip and isometric knee extensor strength were assessed. Weight loss was greater in LC compared with HC (8.4 ± 0.4% and 6.7 ± 0.5%, respectively; P = 0.01 time × diet). Peak oxygen uptake and heart rate were unchanged in both groups (P > 0.17). Fat oxidation increased during submaximal exercise in LC but not HC (P < 0.001 time × diet effect). On both diets, perception of effort during submaximal exercise and handgrip strength decreased (P ≤ 0.03 for time), but knee extensor strength remained unchanged (P > 0.25). An LC weight loss diet shifted fuel utilization toward greater fat oxidation during exercise, but had no detrimental effect on maximal or submaximal markers of aerobic exercise performance or muscle strength compared with an HC diet. Further studies are required to determine the interaction of LC diets with regular exercise training and the long‐term health effects.     

Effects of Chromium and Carnitine Co-supplementation on Body Weight and Metabolic Profiles in Overweight and Obese Women with Polycystic Ovary Syndrome: a Randomized,Double-Blind,Placebo-Controlled Trial

The primary aim of our study was to determine the influence of taking chromium plus carnitine on insulin resistance, with a secondary objective of evaluating the influences on lipid profiles and weight loss in overweight subjects with polycystic ovary syndrome (PCOS). In a 12-week randomized, double-blind, placebo-controlled clinical trial, 54 overweight women were randomly assigned to receive either supplements (200 μg/day chromium picolinate plus 1000 mg/day carnitine) or placebo (27/each group). Chromium and carnitine co-supplementation decreased weight (− 3.6 ± 1.8 vs. − 1.0 ± 0.7 kg, P < 0.001), BMI (− 1.3 ± 0.7 vs. − 0.3 ± 0.3 kg/m², P < 0.001), fasting plasma glucose (FPG) (− 5.1 ± 6.0 vs. − 1.1 ± 4.9 mg/dL, P = 0.01), insulin (− 2.0 ± 1.4 vs. − 0.2 ± 1.2 μIU/mL, P < 0.001), insulin resistance (− 0.5 ± 0.4 vs. − 0.04 ± 0.3, P < 0.001), triglycerides (− 18.0 ± 25.2 vs. + 5.5 ± 14.4 mg/dL, P < 0.001), total (− 17.0 ± 20.3 vs. + 3.6 ± 12.0 mg/dL, P < 0.001), and LDL cholesterol (− 13.3 ± 19.2 vs. + 1.4 ± 13.3 mg/dL, P = 0.002), and elevated insulin sensitivity (+ 0.007 ± 0.005 vs. + 0.002 ± 0.005, P < 0.001). In addition, co-supplementation upregulated peroxisome proliferator-activated receptor gamma (P = 0.02) and low-density lipoprotein receptor expression (P = 0.02). Overall, chromium and carnitine co-supplementation for 12 weeks to overweight women with PCOS had beneficial effects on body weight, glycemic control, lipid profiles except HDL cholesterol levels, and gene expression of PPAR-γ and LDLR. Clinical trial registration number: http://www.irct.ir: IRCT20170513033941N38.