High sodium intake is associated with short leukocyte telomere length in overweight and obese adolescents.

BACKGROUND/OBJECTIVES: Telomere shortening has an important role in cellular aging. However, the impact of high sodium intake, an important risk factor of age-related diseases, on telomere shortening remains unknown. Therefore, we examined the relationship between high dietary sodium intake and leukocyte telomere length (LTL), particularly in the context of obesity, as obesity increases salt sensitivity. SUBJECTS/METHODS: LTL was determined by a quantitative polymerase chain reaction method in 766 adolescents aged 14-18 years (50% females, 49% African Americans). Dietary sodium intake was assessed by seven independent 24-h dietary recalls. We divided the sample into low sodium (mean 2388±522 mg per day) or high sodium groups (mean 4142±882 mg per day) based on the median value (3280.9 mg per day). RESULTS: In the entire cohort, there was no significant association between sodium intake and LTL (r=-0.05, P=0.24). However, there was a significant interaction between sodium intake and obesity status (P=0.049). Further multiple linear regression analyses revealed that higher dietary sodium intake was associated with shorter LTL in the overweight/obese group (body mass index ⩾85th percentile, ß=-0.37, P=0.04), but not in the normal-weight group (ß=0.01, P=0.93) after adjusting for multiple confounding factors. In the overweight/obese group, LTL was significantly shorter in the high sodium intake subjects vs low sodium intake subjects (1.24±0.22 vs. 1.32±0.20, P=0.02), but not the normal-weight group (1.29±0.24 vs 1.30±0.24, P=0.69). CONCLUSIONS: Higher dietary sodium intake is associated with shorter telomere length in overweight and obese adolescents.

[Differential role of physical activity and diet in the prevention of childhood obesity: pre-eminence of physical activity]. / Rôle différentiel de l'activité physique et de l'alimentation dans la prévention de l'obésité infantile: prééminence de l'activité physique.

The current theory, known as the "theory ofenergy balance", perceives paediatric obesity, like adults' obesity, as the result of an excessively positive energy balance. Thus, prevention endeavours have focused on controlling calories intake and dietary education, with increases in physical activity (PA) having just a supporting role. Paradoxically, preventive programmes developed with this vision are not satisfactory, whereas some recent findings suggest, that in the growing body of youths, PA may stimulate stem cells to differentiate preferentially into lean tissue. These observations advocate the emergence of a new theoretical framework to childhood obesity prevention: the "developmental theory", which posits the pre-eminence of PA. As a result, preventive strategies that would emphasise vigorous PA rather than food intake control can help youths develop lean bodies, at the same time that they ingest sufficient amounts of the energy and accompanying nutrients needed for a healthy growth.

Diet vs exercise for the prevention of pediatric obesity: the role of exercise.

As pediatric obesity is commonly viewed as the result of an excessively positive energy balance, preventive efforts typically emphasize reduction of energy intake, with increases in physical activity (PA) having a supporting role. However, recent research that has focused on body composition rather than weight has found that PA stimulates development of lean tissue rather than fat tissue. Preventive interventions that emphasize vigorous PA rather than restriction of energy intake can help youths to develop lean bodies, at the same time that they ingest sufficient amounts of the energy and accompanying nutrients needed for healthy growth.

Associations between muscle mass, physical activity and dietary behaviour in adolescents.

BACKGROUND AND OBJECTIVES: Investigations in older individuals suggest that adequate nutrition and physical activity are particularly important to skeletal muscle health; however, data in adolescents are scant and equivocal. The objective was to determine the associations among diet, physical activity and skeletal muscle mass in adolescents. METHODS: We assessed diet with four to seven 24-h recalls and physical activity by accelerometry in 640 adolescents. Using total body measures of fat-free soft tissue mass and fat mass assessed by dual-energy X-ray absorptiometry, the skeletal muscle mass index (SMMI) was derived by adjusting fat-free soft tissue mass for fat mass in addition to height. RESULTS: Skeletal muscle mass index (SMMI) was negatively associated with consumption of sugar-sweetened beverages (standardized beta coefficient [ß] = -0.10, P = 0.001) and saturated fats (ß = -0.28, P < 0.001). SMMI was positively associated with physical activity (moderate + vigorous) (ß = 0.20, P < 0.001). In further analysis, we observed a significant interaction between physical activity and sugar-sweetened beverage intake on SMMI (P = 0.002). CONCLUSION: Our study in adolescence suggests that physical activity and consumption of both sugar-sweetened beverages and saturated fats are associated with skeletal muscle mass. More importantly, our findings suggest that sugar-sweetened beverage intake may attenuate the beneficial effects of physical activity on skeletal muscle mass.

Thermic effect of food at rest, during exercise, and after exercise in lean and obese men of similar body weight.

The thermic effect of food at rest, during 30 min of cycle ergometer exercise, and after exercise was studied in eight lean (mean +/- SEM, 10 +/- 1% body fat, hydrostatically-determined) and eight obese men (30 +/- 2% body fat). The lean and obese mean were matched with respect to age, height, weight, and body mass index (BMI) to determine the relationship between thermogenesis and body composition, independent of body weight. All men were overweight, defined as a BMI between 26-34, but the obese had three times more body fat and significantly less lean body mass than the lean men. Metabolic rate was measured by indirect calorimetry under four conditions on separate mornings, in randomized order, after an overnight fast: 3 h of rest in the postabsorptive state; 3 h of rest after a 750-kcal mixed meal (14% protein, 31.5% fat, and 54.5% carbohydrate); during 30 min of cycling and for 3 h post exercise in the postabsorptive state; and during 30 min of cycling performed 30 min after the test meal and for 3 h post exercise. The thermic effect of food, which is the difference between postabsorptive and postprandial energy expenditure, was significantly higher for the lean than the obese men under the rest, post exercise, and exercise conditions: the increments in metabolic rate for the lean and obese men, respectively, were 48 +/- 7 vs. 28 +/- 4 kcal over 3 h rest (P less than 0.05); 44 +/- 7 vs. 16 +/- 5 kcal over 3 h post exercise (P less than 0.05); and 19 +/- 3 vs. 6 +/- 3 kcal over 30 min of exercise (P less than 0.05). The thermic effect of food was significantly negatively related to body fat content under the rest (r = -0.55), post exercise (r = -0.66), and exercise (r = -0.58) conditions. The results of this study indicate that for men of similar total body weight and BMI, body composition is a significant determinant of postprandial thermogenesis; the responses of obese are significantly blunted compared with those of lean men.

Body composition, not body weight, is related to cardiovascular disease risk factors and sex hormone levels in men.

To clarify the independent relationships of obesity and overweight to cardiovascular disease risk factors and sex steroid levels, three age-matched groups of men were studied: (i) 8 normal weight men, less than 15% body fat, by hydrostatic weighing; (ii) 16 overweight, obese men, greater than 25% body fat and 135-160% of ideal body weight (IBW); and (iii) 8 overweight, lean men, 135-160% IBW, but less than 15% fat. Diastolic blood pressure was significantly greater for the obese (mean +/- SEM, 82 +/- 2 mmHg) than the normal (71 +/- 2) and overweight lean (72 +/- 2) groups, as were low density lipoprotein levels (131 +/- 9 vs. 98 + 11 and 98 + 14 mg/dl), the ratio of high density lipoprotein to total cholesterol (0.207 +/- 0.01 vs. 0.308 +/- 0.03 and 0.302 +/- 0.03), fasting plasma insulin (22 +/- 3 vs. 12 +/- 1 and 13 +/- 2 microU/ml), and the estradiol/testosterone ratio (0.076 +/- 0.01 vs. 0.042 +/- 0.02 and 0.052 +/- 0.02); P less than 0.05. Estradiol was 25% greater for the overweight lean group (40 +/- 5 pg/ml) than the obese (30 +/- 3 pg/ml) and normal groups (29 +/- 2 pg/ml), P = 0.08, whereas total testosterone was significantly lower in the obese (499 +/- 33 ng/dl) compared with the normal and overweight, lean groups (759 +/- 98 and 797 +/- 82 ng/dl). Estradiol was uncorrelated with risk factors and the estradiol/testosterone ratio appeared to be a function of the reduced testosterone levels in obesity, not independently correlated with lipid levels after adjustment for body fat content. Furthermore, no risk factors were significantly different between the normal and overweight lean groups. We conclude that (a) body composition, rather than body weight per se, is associated with increased cardiovascular disease risk factors; and (b) sex steroid alterations are related to body composition and are not an independent cardiovascular disease risk factor.

Thermic effect of food during graded exercise in normal weight and obese men.

The thermic effect of food during incremental cycle ergometer exercise was compared in six normal weight and six obese men (mean +/- SEM 104 +/- 5% and 160 +/- 11% ideal body weight, respectively). Graded exercise tests were performed after a 12-h fast and 60 min after the start of a 910 kcal mixed meal, on separate days. The thermic of food during exercise, which is the fed minus the fasting oxygen consumption (VO2), was significantly greater for the normal than the obese men at submaximal intensities from O (unloaded cycling) to 100 W (p less than 0.05). The mean slope of the regressions of VO2 (ml . min-1) on power output (W), which reflects the rate of increase in energy expended relative to increases in external work performed, did not differ significantly between the fed and fasting conditions for either group, but the mean (+/- SEM) intercept was significantly higher for the normal, but not the obese men, in the fed than the fasting state (599 +/- 53 versus 497 +/- 47 ml O2 . min-1 for the normal men and 819 +/- 126 versus 821 +/- 145 ml O2 . min-1 for the obese men). These results indicate that the thermic effect of food during exercise, which is virtually absent in the obese men, does not increase significantly across submaximal power outputs for the normal men and therefore does not reflect a significant reduction in efficiency.

Effects of strength or aerobic training on body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects.

Given that resting metabolic rate (RMR) is related largely to the amount of fat-free mass (FFM), the hypothesis was that strength training, which stimulates muscle hypertrophy, would help preserve both FFM and RMR during dieting. In a randomized controlled intervention trial, moderately obese subjects (aged 19-48 y) were assigned to one of three groups: diet plus strength training, diet plus aerobic training, or diet only. Sixty-five subjects (25 men and 40 women) completed the study. They received a formula diet with an energy content of 70% of RMR or 5150 +/- 1070 kJ/d (x +/- SD) during the 8-wk intervention. They were seen weekly for individual nutritional counseling. Subjects in the two exercise groups, designed to be isoenergetic, trained three times per week under supervision. Those in the strength-training group performed progressive weight-resistance exercises for the upper and lower body. Those in the aerobic group performed alternate leg and arm cycling. After 8 wk, the mean amount of weight lost, 9.0 kg, did not differ significantly among groups. The strength-training group, however, lost significantly less FFM (P < 0.05) than the aerobic and diet-only groups. The strength-training group also showed significant increases (P < 0.05) in anthropometrically measured flexed arm muscle mass and grip strength. Mean RMR declined significantly, without differing among groups. Peak oxygen consumption increased the most for the aerobic group (P = 0.03). In conclusion, strength training significantly reduced the loss of FFM during dieting but did not prevent the decline in RMR.

Effects of physical training and its cessation on the hemostatic system of obese children.

BACKGROUND: Physical training can improve hemostatic function in adults, thereby reducing heart disease risk, but no information is available in children on whether physical training can enhance hemostatic function. OBJECTIVE: The purpose of this investigation was to examine the effects of a physical training program on hemostatic variables in a biethnic group of obese children. DESIGN: Children were randomly assigned to 2 groups. Group 1 participated in physical training for 4 mo and then ceased physical training for 4 mo, whereas group 2 did no physical training for the first 4 mo and then participated in physical training for 4 mo. Plasma hemostatic variables [fibrinogen, plasminogen activator inhibitor 1 (PAI-1), and D-dimer) were measured at months 0, 4, and 8. RESULTS: Analyses of variance revealed no significant group-by-time interactions for the hemostatic variables. When data from both groups were combined there was a significant decrease in D-dimer after 4 mo of physical training (P < 0.05). Factors explaining individual differences in responsiveness to the physical training revealed that individuals with greater percentage fat before physical training showed greater reductions in fibrinogen and D-dimer, and that blacks showed greater reductions in D-dimer than whites (P < 0.05). Stepwise multiple linear regression showed that only higher prephysical training concentrations of fibrinogen, PAI-1, and D-dimer explained significant proportions of the variation in changes in these variables. CONCLUSIONS: In obese children, 4-mo periods of physical training did not lead to significant changes in hemostatic variables. Children with greater adiposity and concentrations of hemostatic factors before physical training showed greater reductions in hemostatic variables after physical training than did children with lesser values.

Correlates of individual differences in body-composition changes resulting from physical training in obese children.

BACKGROUND: No studies have been reported in children that assess correlates of body-composition changes in response to a physical training intervention. OBJECTIVE: The hypothesis studied was that variation in diet and physical activity would explain a significant portion of the interindividual variation in the response of body composition to physical training. DESIGN: The participants were 71 obese children aged 7-11 y (22 boys, 49 girls; 31 whites, 40 blacks). Body composition was measured by dual-energy X-ray absorptiometry, physical activity by a 7-d recall interview, and diet by two, 2-d recalls. The children underwent 4 mo of physical training. RESULTS: The mean attendance was 4 d/wk, the mean (+/-SD) heart rate for the 40-min sessions was 157 +/- 7 beats/min, and the mean energy expenditure was 946 +/- 201 kJ/session. On average, the percentage body fat decreased significantly in the total group, and total mass, fat-free soft tissue, bone mineral content, and bone mineral density increased, but there was a good deal of individual variability. Multiple regression models indicated that in general, more frequent attendance, being a boy, lower energy intake, and more vigorous activity were associated with healthier body-composition changes with physical training. Ethnicity was not retained as a correlate of the change of any component of body composition. CONCLUSIONS: In obese children, age, vigorous activity, diet, and baseline percentage body fat together accounted for 25% of the variance in the change in percentage body fat with physical training.

Plasma leptin concentrations in obese children: changes during 4-mo periods with and without physical training.

BACKGROUND: Little is known about the effects of physical training on plasma leptin concentrations in children. OBJECTIVE: We sought to determine the effects of 4-mo periods with and without physical training on leptin in obese children and to explore the determinants of leptin at baseline and in response to physical training. DESIGN: Participants were 34 obese 7-11-y-old children randomly assigned to engage in physical training during either the first or second 4 mo of the 8-mo study. RESULTS: Total body composition, visceral adiposity, and insulin were all positively correlated with leptin at baseline (P < or = 0.05); however, only fat mass was retained in the final stepwise regression (P = 0.0001, R2 = 0.57). Leptin decreased during the 4-mo periods of physical training and increased in the 4 mo after cessation of physical training (P < 0.001 for the time by group interaction). Decreases in leptin were greatest in children with higher pretraining leptin concentrations, those whose total mass increased least, and those whose insulin concentrations decreased most (P < or = 0.05); only pretraining leptin concentration (P = 0.009) and change in total mass (P = 0.0002) were retained in the final regression (R2 = 0.53). CONCLUSIONS: In obese children, leptin concentration decreased during 4 mo of physical training and increased during a subsequent 4-mo period without physical training, fat mass was highly correlated with baseline leptin, and greater reductions in leptin during 4 mo of physical training were seen in children with higher pretraining leptin and in those whose total mass increased least.

Fat distribution and hemostatic measures in obese children.

We examined the relation of general and visceral adiposity to plasma hemostatic factors [fibrinogen, D-dimer, and plasminogen activator inhibitor 1 (PAI-1)] in obese boys and girls 7-11 y of age (n = 41). Boys had significantly greater fibrinogen and D-dimer concentrations than girls (P < 0.05). whereas blacks had significantly greater fibrinogen and D-dimer concentrations than whites (P < 0.05). Univariate analyses revealed that fibrinogen was positively associated with percentage body fat (%BF) (r = 0.42, P < 0.01), subcutaneous abdominal adipose tissue (SAAT) (r = 0.40, P < 0.01), total fat mass (r = 0.42, P < 0.01), and body mass index (r = 0.41, P < 0.01). PAI-1 was positively associated with visceral adipose tissue (VAT) (r = 0.49, P < 0.01), SAAT (r = 0.32, P < 0.05), fat-free mass (r = 0.50, P < 0.01), and insulin (r = 0.61, P < 0.001). D-Dimer was positively associated with %BF (r = 0.40, P < 0.01), SAAT (r = 0.37, P < 0.05), total fat mass (r = 0.40, P < 0.01), and body mass index (r = 0.43, P < 0.01). Multiple regression analysis revealed that for fibrinogen, sex and higher %BF explained significant independent portions of the variance. For PAI-1, higher amounts of VAT and fat-free mass were significant predictors. For D-dimer, ethnicity was a significant predictor. These results suggest that general adiposity and VAT may play a role in regulating plasma hemostatic factors in obese children. Even early in childhood, adiposity is associated with unfavorable concentrations of hemostatic factors that are in turn implicated in cardiovascular morbidity and mortality later in life.

Body-composition measurement in 9-11-y-old children by dual-energy X-ray absorptiometry, skinfold-thickness measurements, and bioimpedance analysis.

We compared, in 9-11-y-old children (n=43), three measures of body composition: dual-energy X-ray absorptiometry (DXA), skinfold thickness, and bioimpedance analysis (BIA). The intraclass correlation coefficient (ICC), Bland-Altman procedure, and Spearman rank correlation were used to determine test-retest reliabilities of the three methods and to compare methods. For DXA measurements, the rank correlation between fat-free soft tissue and fat-free mass (FFM) was > 0.99, indicating that bone mineral content did not provide independent information. Thus, subsequent analyses used the two-compartment model (ie, fat mass and FFM) for all three techniques, focusing especially on values for percentage of fat. The test-retest reliabilities for all methods were high (ICCs > 0.994 and no significant differences between trials 1 and 2). The range of individual differences from trial 1 to trial 2 and Bland-Altman limits of agreement suggested that the reliability was greatest for DXA, followed by BIA and skinfold-thickness measurement. The percentage of fat values for the three methods were highly intercorrelated (all Spearman r values > 0.83). However, there was a systematic tendency (P < 0.01) for DXA values (mean: 23.98) to be higher than those derived from skinfold-thickness measurements (mean: 21.05) and BIA (mean: 21.52). The variance in percentage of fat values for BIA was significantly smaller than that for the other two techniques. These findings, along with rather large limits of agreement derived from the Bland-Altman procedure, suggest that the methods should not be used interchangeably.

Levels of serum sex hormones and risk factors for coronary heart disease in exercise-trained men.

On the basis of previous findings, it has been hypothesized that hyperestrogenemia may be the major predisposing factor for coronary heart disease and that an elevation in the estradiol-to-testosterone ratio, or a closely related hormonal alteration, may cause the expression of risk factors for coronary heart disease. The present study was carried out to investigate whether exercise training, which has been reported to reduce risk factors for coronary heart disease, affects the serum sex hormone levels. The serum sex hormone levels, established risk factors for coronary heart disease, and physical fitness were measured in 10 men who had undergone at least six months of intensive exercise training and in 10 sedentary men of similar age. Despite evidence for a strikingly higher level of physical fitness and a lower level of risk factors in the trained group, no significant difference in mean serum estradiol level was found. Nor did three subjects from the sedentary group show a decrease in estradiol level after three to four months of exercise training. The mean estradiol-to-testosterone ratio, however, was significantly lower in the trained group and might account for the lower level of risk factors in that group. If the hypothesis is correct, exercise training may decrease established risk factors for coronary heart disease without decreasing the risk of coronary heart disease.

Fasting insulin concentration is related to cardiovascular reactivity to exercise in children.

OBJECTIVE: One mechanism through which hyperinsulinemia is linked to hypertension is through its stimulation of sympathetic nervous activity. Thus, insulin concentration may be correlated with indices of sympathetic activity before it is associated with resting blood pressure. We tested this hypothesis by determining the relationship of insulin concentration and sympathetically mediated cardiovascular reactivity to exercise in children. DESIGN: Survey. SETTING: General community. PARTICIPANTS: Volunteer sample of 46 black and white boys and girls, 9 to 11 years of age. INTERVENTIONS: None. Fasting insulin concentration was the main independent variable. MAIN OUTCOME MEASURES: Systolic blood pressure and heart rate during a standard submaximal bout of treadmill exercise, and systolic blood pressure at peak effort. RESULTS: The hypothesis was tested by multiple regression analyses controlled for resting values. Insulin contributed significantly to the regression models for submaximal heart rate (P < .001), submaximal systolic blood pressure (P = .001), and peak systolic blood pressure (P = .006). CONCLUSIONS: Fasting insulin concentration is associated with cardiovascular reactivity to exercise in young children. This supports the hypothesis that the relationship between hyperinsulinemia and hypertension is mediated by sympathetic nervous tone and that the process begins in childhood. Because percent body fat was positively associated with both insulin and cardiovascular reactivity to exercise, prevention of childhood obesity may be a valuable prophylactic measure for these health problems.

Low density lipoprotein cholesterol/apolipoprotein B-100 ratio: interaction of family history of premature atherosclerotic coronary artery disease with race and gender in 7 to 11 year olds.

BACKGROUND: In adults, a low density lipoprotein cholesterol (LDL-C)/apolipoprotein B-100 (ApoB) ratio is an indicator of ApoB-enriched small dense LDL, which is associated with premature coronary artery disease (CAD). Since this LDL subclass may be inherited, we investigated whether a low LDL-C/ApoB ratio was associated with a positive family history of premature CAD in young children. METHODS: Subjects were 66 children aged 7 to 11 years who were recruited through a school-based family history survey, flyers, and hospital newspaper advertisements. They were divided according to family history and assessed for fatness, blood pressure, lipids, lipoproteins, and apoproteins. RESULTS: Family history interacted with gender such that girls with a positive family history had a lower LDL-C/ApoB ratio than girls with a negative family history, while the opposite was true in boys; ie, family history-positive boys had a higher ratio than family history-negative boys. The association of a low ratio with a positive family history was seen most clearly in white girls. Family history-positive whites had higher ApoB than family history-negative whites, whereas the pattern was reversed in the blacks. The LDL-C/ApoB ratio and ApoB were not related to other CAD risk factors such as fatness, blood pressure, or other lipids and lipoproteins. CONCLUSION: In young children, a low LDL-C/ApoB ratio and high ApoB levels were associated with a positive family history of CAD only in the white girls, suggesting that this group is at increased risk of genetically mediated CAD.

The rate of increase in blood pressure in children 5 years of age is related to changes in aerobic fitness and body mass index.

OBJECTIVE: To determine whether changes in aerobic fitness and body mass index are related to the age-related rise in blood pressure in healthy preschool children. STUDY DESIGN: Longitudinal analyses of 196 free-living children aged 5 years at baseline who were followed over a mean of 19.7 months. Aerobic fitness was assessed using a treadmill. All measures were obtained on multiple occasions at scheduled visits as part of a longitudinal cohort study. SETTING: An inner-city medical center. OUTCOME MEASURES: Blood pressure was measured using an automated Dinamap device. RESULTS: Mean systolic blood pressure was 95.3 mmHg (SD 8.38) at baseline and increased by 4.46 mmHg per year. Mean diastolic blood pressure was 53.9 mmHg (SD 5.81) at baseline and did not change significantly. Children in the highest quintile of increase in fitness had a significantly smaller increase in systolic blood pressure compared to children in the lowest quintile (2.92 vs 5.10 mmHg/year; P = .03). Children in the lowest quintile of increase in body mass index did not differ significantly in rate of increase in systolic blood pressure compared to children in the highest quintile (3.92 vs 4.96 mmHg/year). In a multiple regression model including baseline systolic blood pressure, fitness, height, body mass index, and other covariates, greater increase in fitness (P = .03) and lesser increase in body mass index (P < .01) were associated with lower rates of increase in systolic blood pressure. In a similar multivariate analysis, an increase in fitness was also associated with a lower rate of increase in diastolic blood pressure (P = .02). CONCLUSION: Young children who increase their aerobic fitness or decrease their body mass index reduce the rate of the age-related increase in blood pressure. These observations may have implications for development of interventions directed at the primary prevention of hypertension.

Exercise in sickle cell anemia: effect on inflammatory and vasoactive mediators.

The aim of this study was to determine the response of inflammatory and vasoactive mediators to 3 consecutive days of exercise in African-American women with and without sickle cell anemia (SCA). Circulating inflammatory mediators [C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha)] were measured before, and vasoactive mediators [endothelin-1 (ET-1), nitric oxide metabolites (NOx)] before and after each exercise bout in ten subjects with SCA and ten controls. Exercise did not affect ET-1, IL-6 or CRP concentrations (p >.05). TNFalpha was higher in SCA than controls (p < or = .0005) at all times; however, the response pattern was similar for the groups: no change from day 1 to day 2, but a decrease from day 2 to day 3 (p < or = .05). NOx increased significantly after exercise (p < or = .0001) but returned to baseline by 24 h afterward. On the 3rd day, NOx increased after exercise in SCA but not in the controls (p < or = .05). In conclusion, exercise did not cause a harmful inflammatory response in these individuals with SCA. However, NOx increased after exercise on all 3 days in SCA but appeared attenuated after 2 days in controls.

Thermic effects of food and exercise in lean and obese women.

The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P less than 0.005). Exercise potentiated the thermic effect of food for the lean women but nor for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P less than 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.

Comparison in man of total body electrical conductivity and lean body mass derived from body density: validation of a new body composition method.

This article reports a study in which total body electrical conductivity (TOBEC) measurements and lean body mass (LBM) estimated from hydrostatic weighing in human subjects were compared. The TOBEC method provides a new approach to assessment of human body composition that is based on the principle that the electrical conductivity of lean tissue is far greater than that of fat. In a sample of 32 men and women varying widely in age (20 to 53 years), body weight (45 to 155 kg), and adiposity (9.5 to 53.0% body fat), the TOBEC measurement was found to be extremely reliable (r = 0.999) and to correlate highly with hydrostatically estimated LBM (r = 0.903, P less than 0.0001). When the TOBEC scores were transformed to provide a single variable; namely, the subject's height times the square root of the TOBEC score, a higher correlation with LBM was obtained (r = 0.943). Taking gender into account further enhanced the prediction of LBM from TOBEC (r = 0.951). These observations strongly reinforce the results of a previous investigation in which high correlations were found between TOBEC and both total body potassium and total body water. Accordingly, this new method promises to provide a useful technique for the evaluation of body composition that is at once simple, rapid, objective, and noninvasive.