The effect of time of day on short-term maximal performance in obese and non-obese young men

The purpose of this study was to examine time-of-day effects on short-term performance in obese young men. In a balanced study design, 30 boys were divided into two groups: obese (OG; n = 15) and non-obese (CG; n = 15) groups. Both groups performed anaerobic tests of strength and power (squat-Jump, SJ; counter-movement jump, CMJ; 10-m sprint; and 30-m sprint) at 08:00 and 17:00 h on separate days. The results showed morning–evening differences in all variables in CG, with significant increases at 17:00 h (around the time of peak temperature) in comparison with 08:00 h (p < 0.01) for OG. However, such morning-evening differences were not found in the OG, except for the 30-m sprint. Obesity affects the diurnal variation on performances of 30-m sprint with a significant decrease in the evening for OG of 1.23% (p < 0.01). A correlation between anaerobic performance and oral temperature was observed only in the 30-m sprint test. In conclusion, the findings of the present study indicated that obesity is a problem that can affect circadian rhythms and performance in obese young men; therefore, preventing childhood obesity should become a top priority in efforts to improve performance and health.     

Plasma leptin in moderately obese men: independent effects of weight loss and aerobic exercise

The independent effects of weight loss and exercise on plasma leptin and total (AT), subcutaneous (SAT), and visceral (VAT) adipose tissue were investigated in 52 obese men. Subjects were randomly assigned to four 12-wk protocols: 1) control (C, n = 8), 2) diet-induced weight loss (DWL, n = 14), 3) exercise-induced weight loss (EWL, n = 14), and 4) exercise with weight maintenance (EWS, n = 16). Plasma leptin was unchanged in C (from 7.8 +/- 1.3 to 7.7 +/- 1.0 ng/ml). Equivalent weight loss (7.5 kg) decreased leptin significantly but similarly (DWL, from 8.5 +/- 1.0 to 4.8 +/- 0.6 ng/ml; EWL, from 10.1 +/- 1.0 to 5.0 +/- 0.6 ng/ml). Exercise in the absence of weight loss did not alter leptin levels (from 10.1 +/- 1. 3 to 9.2 +/- 1.2 ng/ml). Changes in leptin correlated with changes in AT and SAT (both P < 0.05) but not in VAT. We conclude that reduction in adipose tissue after weight loss results in a collateral decrease in circulating leptin, and exercise, independent of its effects on weight loss, has no profound influence on leptin secretion.     

Independent metabolic costs of supporting body weight and accelerating body mass during walking.

The metabolic cost of walking is determined by many mechanical tasks, but the individual contribution of each task remains unclear. We hypothesized that the force generated to support body weight and the work performed to redirect and accelerate body mass each individually incur a significant metabolic cost during normal walking. To test our hypothesis, we measured changes in metabolic rate in response to combinations of simulated reduced gravity and added loading. We found that reducing body weight by simulating reduced gravity modestly decreased net metabolic rate. By calculating the metabolic cost per Newton of reduced body weight, we deduced that generating force to support body weight comprises approximately 28% of the metabolic cost of normal walking. Similar to previous loading studies, we found that adding both weight and mass increased net metabolic rate in more than direct proportion to load. However, when we added mass alone by using a combination of simulated reduced gravity and added load, net metabolic rate increased about one-half as much as when we added both weight and mass. By calculating the cost per kilogram of added mass, we deduced that the work performed on the center of mass comprises approximately 45% of the metabolic cost of normal walking. Our findings support the hypothesis that force and work each incur a significant metabolic cost. Specifically, the cost of performing work to redirect and accelerate the center of mass is almost twice as great as the cost of generating force to support body weight.     

Gender differences in predictors of body weight and body weight change in healthy adults

Background: Overweight and obesity are important predictors of a wide variety of health problems. Analysis of naturally occurring changes in body weight can provide valuable insights in improving our understanding of the influence of demographic, lifestyle, and psychosocial factors on weight gain in middle‐age adults. Objective: To identify gender‐specific predictors of body weight using cross‐sectional and longitudinal analyses. Methods and Procedures: Anthropometric, lifestyle and psychosocial factors were measured at baseline and then quarterly for 1 year in 572 healthy adult volunteers from Central Massachusetts who were recruited between 1994 and 1998. Linear mixed models were used to analyze the relationship between body weight and potential predictors, including demographic (e.g., age, educational level), lifestyle (e.g., diet, physical activity, smoking), and psychosocial (e.g., anxiety, depression) factors. Results: Over the 1‐year study period, on average, men gained 0.3 kg and women lost 0.2 kg. Predictors of lower body weight at baseline in both men and women included current cigarette smoking, greater leisure‐time physical activity, and lower depression and anxiety scores. Lower body weights were associated with a lower percentage of caloric intake from protein and greater occupational physical activity levels only among men; and with higher education level only among women. Longitudinal predictors of 1‐year weight gain among women included increased total caloric intake and decreased leisure‐time physical activity, and among men, greater anxiety scores. Discussion: Demographic, lifestyle and psychosocial factors are independently related to naturally occurring changes in body weight and have marked differential gender effects. These effects should be taken into consideration when designing interventions for weight‐loss and maintenance at the individual and population levels.     

Blood pressure control during weight reduction in obese hypertensive men: separate effects of sodium and energy restriction.

The separate and combined effects of dietary energy and sodium restriction on regulation of blood pressure were investigated in 30 middle aged obese men with essential hypertension attending the outpatient department. In group 1 (n = 15) a basal period with no dietary restriction was followed by a period taking an energy reduced diet (5.1 MJ; 1230 kcal), the sodium intake being supplemented and hence unchanged (1:ErSn). In group 2 (n = 15) the basal period preceded a control period with no intervention, which was followed by taking a diet restricted in energy (5.1 MJ; 1220 kcal) and sodium (2:ErSr). During period 1:ErSn there were reductions in heart rate and urinary noradrenaline output but not in systolic or diastolic blood pressure. Body weight decreased by 4.9-11.7 kg and urinary sodium excretion did not change. In period 2:ErSr urinary sodium output was reduced by 81.4 (SEM 17.8) mmol(mEq)/24 h and there was a weight loss of 8.2 (SEM 0.7) kg. Systolic and diastolic blood pressures fell significantly, as did the heart rate and urinary noradrenaline excretion. These results show that in hypertensive obese men a moderate weight reducing diet decreases indices of sympathetic nervous system activity. Reduction of blood pressure to the normotensive range was observed only when there was a concomitant restriction of sodium intake.     

Metabolic effects of weight reduction in obese diabetics and nondiabetics.

A weight loss of about 10 kg was acheived by means of individual periods of total fasting, hypocaloric diets and physical activity in three groups of patients: maturity-onset diabetics, patients with pathological OGTT and overweight persons with normal OGTT. Adipocyte volume decreased in all groups, glucose tolerance improved. IRI curves showed a significant overall lowering and FFA concentrations during OGTT were dimished.     

Leptin and metabolic syndrome in obese and non-obese children.

Metabolic syndrome is characterized by a clustering of metabolic abnormalities: insulin resistance - hyperinsulinemia, dyslipidemia (high triglycerides and low HDL - cholesterol serum concentrations), impaired glucose tolerance and/or type 2 diabetes, and hypertension. The aim of this study was to analyse the role of different variables of metabolic syndrome, including leptin, in 74 non-obese children and 68 children with non-syndromal obesity. As metabolic syndrome variables, we have included body mass index, waist circumference, trunk-to-total skinfolds (%), systolic blood pressure, diastolic blood pressure, glucose, uric acid, fasting insulin, triglycerides and high-density lipoprotein-cholesterol (HDL-C). Factor analysis showed 4 factors in each group. In non-obese children, waist circumference, BMI, fasting insulin, triglycerides, trunk-to-total skinfolds (%), leptin and uric acid loaded positively on factor 1, and HDL-C loaded negatively on this factor; systolic and diastolic blood pressure had high positive loadings in factor 2; HDL-C and leptin showed positive loadings and triglycerides and uric acid, negative loadings in factor 3; and, finally, glucose and insulin showed positive loadings in factor 4. These four factors explained 72.16 % of the total variance in the non-obese group. In obese children, BMI, waist circumference, leptin, diastolic blood pressure and systolic blood pressure loaded positively on factor 1; diastolic blood pressure, trunk-to-total skinfolds (%), uric acid and systolic blood pressure showed high positive loadings in factor 2; fasting insulin, glucose and triglycerides showed positive loadings in factor 3; and, finally, triglycerides showed positive loadings and HDL-C negative loadings in factor 4. These four factors explained 74.18 % of the total variance in the obese group. Our results point to a different homeostatic control of metabolic syndrome characteristics in obese and non-obese children. Leptin seems to play a key underlying role in metabolic syndrome, especially in the obese group.     

The effects of stress on body weight: biological and psychological predictors of change in BMI

Objective: To investigate individual differences in the effects of stress on BMI. Research Methods and Procedures: Participants were 71 healthy women volunteers enrolled in a university‐based nurse practitioner program. Predictors of change in BMI were hypothesized to be cortisol secretion, dietary restraint, bingeing, mastery, mood, and eating attitudes. Measures were made at the beginning of the academic semester and 12 weeks later during the participants’ examination period. Results: The women were of normal weight (BMI 25.2 ± 4.3) for their age [43; standard deviation (SD), 7]. By the examination period, 40 had gained weight (mean, 5.5 pounds; SD, 2.2), 19 lost weight (mean, 2.5 pounds; SD, 1.5), and 12 had stable weight. BMI, salivary cortisol secretion, bingeing behavior, depression, and anxiety increased significantly, whereas scores on dietary restraint, weight, shape, and eating concerns, and mastery decreased significantly. Regression analysis showed that change in daily cortisol secretion significantly predicted change in BMI and that mastery significantly moderated this relationship. However, a reduction in dietary restraint was a perfect mediator of this relationship. Change in cortisol secretion also significantly predicted change in dietary restraint, and this was moderated by dietary restraint at the beginning of the academic semester. Reduction in dietary restraint was also predicted by a reduction in mastery and weight concern. Discussion: We identified individual differences that confer vulnerability to weight gain during stressful life events (dietary restraint and mastery). Given that women are exposed to daily stressors and use cognitive strategies to restrain their dietary intake, increasing awareness of the role of stress on eating behavior and weight is an important goal.     

Exercise effect on weight and body fat in men and women

Objectives: The effect of national exercise recommendations on adiposity is unknown and may differ by sex. We examined long‐term effects of aerobic exercise on adiposity in women and men. Research Methods and Procedures: This was a 12‐month randomized, controlled clinical trial testing exercise effect on weight and body composition in men (N = 102) and women (N = 100). Sedentary/unfit persons, 40 to 75 years old, were recruited through physician practices and media. The intervention was facility‐ and home‐based moderate‐to‐vigorous intensity aerobic activity, 60 min/d, 6 days/wk vs. controls (no intervention). Results: Exercisers exercised a mean 370 min/wk (men) and 295 min/wk (women), and seven dropped the intervention. Exercisers lost weight (women, ?1.4 vs. +0.7 kg in controls, p = 0.008; men, ?1.8 vs. ?0.1 kg in controls, p = 0.03), BMI (women, ?0.6 vs. +0.3 kg/m² in controls, p = 0.006; men, ?0.5 kg/m² vs. no change in controls, p = 0.03), waist circumference (women, ?1.4 vs. +2.2 cm in controls, p < 0.001; men, ?3.3 vs. ?0.4 cm in controls, p = 0.003), and total fat mass (women, ?1.9 vs. +0.2 kg in controls, p = 0.001; men, ?3.0 vs. +0.2 kg in controls, p < 0.001). Exercisers with greater increases in pedometer‐measured steps per day had greater decreases in weight, BMI, body fat, and intra‐abdominal fat (all p trend < 0.05 in both men and women). Similar trends were observed for increased minutes per day of exercise and for increases in maximal oxygen consumption. Discussion: These data support the U.S. Department of Agriculture and Institute of Medicine guidelines of 60 min/d of moderate‐to‐vigorous physical activity.     

Antihypertensive effect of diet compared with drug treatment in obese men with mild hypertension.

OBJECTIVE--To determine whether dietary treatment has a similar antihypertensive effect to conventional drug treatment while being superior to drugs in improving serum lipid concentrations in obese men with mild hypertension. DESIGN--Six week run in period followed by randomisation to either diet or drug treatment groups for one year. SETTING--Outpatient clinic in city hospital. PATIENTS--61 Men aged 40-69 years, body mass index greater than or equal to 26, diastolic blood pressure 90-104 mm Hg when untreated. Exclusion criteria were signs of organ damage secondary to hypertension and diseases that might have interfered with compliance or with interpretation of results. INTERVENTIONS--Dietary treatment was based on weight reduction, restriction of sodium, and decrease of excess alcohol intake (defined as greater than or equal to 250 g alcohol per week). Drug treatment used a stepped care approach with atenolol as drug of first choice. MAIN OUTCOME MEASURES--Diastolic blood pressure less than 90 mm Hg; absolute reductions in blood pressure and serum lipid concentrations. RESULTS--Mean body weight decreased 7.6 kg in the diet group and increased 0.9 kg in the drug treatment group (p less than 0.0001), and mean sodium excretion decreased 42 and 10 mmol/24 h respectively (p = 0.019). There was no difference in reported alcohol intake. Mean systolic blood pressure decreased 4 mm Hg in the diet group and 16 mm Hg in the drug group (p = 0.003) and diastolic blood pressure 3 and 11 mm Hg respectively (p = 0.002). Diastolic blood pressure of 90 mm Hg was attained by 29% of the diet group (nine men) and 73% (22) of those receiving drug treatment (mean difference 44%, 95% confidence interval 21 to 67%, p = 0.001). Dietary treatment produced decreases in mean serum concentrations of total and low density lipoprotein cholesterol as well as triglycerides and an increase in high density lipoprotein cholesterol concentration. In the drug treatment group the changes were in the opposite direction, and the groups differed significantly in all but total cholesterol. CONCLUSIONS--Dietary treatment was inferior to conventional drug treatment in controlling mild hypertension but superior in lowering serum concentrations of lipids.