***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Obesity is a major public health problem in the United States . The role of physical activity and formal exercise in controlling body weight has not been clearly determined . OBJECTIVE This study determined the magnitude of change in body weight and composition across sex , race , and age in response to 20 wk of endurance training . DESIGN Men and women ( n = 557 ) of various ages ( 16 - 65 y ) and 2 races ( black and white ) exercised on cycle ergometers 3 d/wk for a total of 60 exercise sessions starting at 55 % of maximal oxygen consumption ( VO(2)max ) for 30 min/session and building to 75 % of VO(2)max for 50 min/session , where it was maintained during the last 6 wk .  Skinfold-thickness measurements , circumferences , body composition ( by hydrostatic weighing ) , and body fat distribution ( by computed tomography scan at L4-L5 and the waist-hip ratio ) were determined before and after training . RESULTS All skinfold-thickness and circumference measures , waist-hip ratio , body mass index , total body mass , fat mass , percentage body fat , and computed tomography scan measures of total , subcutaneous , and visceral abdominal fat decreased with training , whereas total body density and fat-free mass increased . These changes were significant , but small . There were several differences in training response by sex and race , but not by age . CONCLUSIONS A short-term exercise intervention can induce favorable changes in body composition , but the magnitude of these changes is of limited biological significance . Increasing physical activity likely has a major effect on body-composition and fat distribution characteristics only when it is of a greater magnitude and sustained for much longer BACKGROUND Exercise could contribute to weight loss by altering the sensitivity of the appetite regulatory system . OBJECTIVE The aim of this study was to assess the effects of 12 wk of m and atory exercise on appetite control . DESIGN Fifty-eight overweight and obese men and women [ mean ( + /-SD ) body mass index ( in kg/m(2 ) ) = 31.8 + /- 4.5 , age = 39.6 + /- 9.8 y , and maximal oxygen intake = 29.1 + /- 5.7 mL . kg(-1 ) . min(-1 ) ] completed 12 wk of supervised exercise in the laboratory .  The exercise sessions were design ed to expend 2500 kcal/wk . Subjective appetite sensations and the satiating efficiency of a fixed breakfast were compared at baseline ( week 0 ) and at week 12 . An Electronic Appetite Rating System was used to measure subjective appetite sensations immediately before and after the fixed breakfast in the immediate postpr and ial period and across the whole day . The satiety quotient of the breakfast was determined by calculating the change in appetite scores relative to the breakfast 's energy content . RESULTS Despite large variability , there was a significant reduction in mean body weight ( 3.2 + /- 3.6 kg ) , fat mass ( 3.2 + /- 2.2 kg ) , and waist circumference ( 5.0 + /- 3.2 cm ) after 12 wk . The analysis showed that a reduction in body weight and body composition was accompanied by an increase in fasting hunger and in average hunger across the day ( P < 0.0001 ) . Paradoxically , the immediate and delayed satiety quotient of the breakfast also increased significantly ( P < 0.05 ) . CONCLUSIONS These data show that the effect of exercise on appetite regulation involves at least 2 processes : an increase in the overall ( orexigenic ) drive to eat and a concomitant increase in the satiating efficiency of a fixed meal Obesity and physical inactivity are independent risk factors for the development of nonalcoholic fatty liver disease ( NAFLD ) . We determined the effect of endurance exercise training on hepatic lipid content and hepatic enzyme concentration in men and women .  Waist circumference ( WC ) , percent body fat ( BF ) , computed tomography ( CT ) scans for liver attenuation ( inverse relationship with hepatic lipid ) , bilirubin , alanine aminotransferase ( ALT ) , and gamma-glutamyltransferase ( GGT ) plasma concentrations were measured before and after 12 weeks of endurance training in 41 lean and obese men and women .  Exercise training did not change liver attenuation , body weight , percent BF , bilirubin , or ALT concentration , but did lower WC ( P < 0.0001 ) , and decreased GGT in men only ( P = 0.01 ) . Obese subjects had a lower liver attenuation than lean subjects ( P = 0.04 ) . Obese women had lower ALT than obese men ( P = 0.03 ) . GGT was lower in women before and after training . WC was positively correlated with GGT ( r = 0.32 , P = 0.003 ) and ALT ( r = 0.320 , P = 0.004 ) and negatively correlated with liver attenuation ( r = -0.340 , P = 0.03 ) . Percent BF was negatively correlated with bilirubin ( r = -0.374 , P = 0.005 ) . Liver attenuation was negatively correlated with ALT ( r = -0.405 , P = 0.003 ) . Short-term endurance training without weight loss does not alter hepatic lipid content . There was a strong relationship between GGT/ALT and body composition ( percent BF ) as well as between ALT and hepatic lipid content BACKGROUND Obesity is a major health problem due , in part , to physical inactivity . The amount of activity needed to prevent weight gain is unknown . OBJECTIVE To determine the effects of different amounts and intensities of exercise training . DESIGN R and omized controlled trial ( February 1999-July 2002 ) . SETTING AND PARTICIPANTS Sedentary , overweight men and women ( aged 40 - 65 years ) with mild to moderate dyslipidemia were recruited from Durham , NC , and surrounding communities . INTERVENTIONS Eight-month exercise program with 3 groups : ( 1 ) high amount/vigorous intensity ( calorically equivalent to approximately 20 miles [ 32.0 km ] of jogging per week at 65%-80 % peak oxygen consumption ) ; ( 2 ) low amount/vigorous intensity ( equivalent to approximately 12 miles [ 19.2 km ] of jogging per week at 65%-80 % ) , and ( 3 ) low amount/moderate intensity ( equivalent to approximately 12 miles [ 19.2 km ] of walking per week at 40%-55 % ) . Subjects were counseled not to change their diet and were encouraged to maintain body weight . MAIN OUTCOME MEASURES Body weight , body composition ( via skinfolds ) , and waist circumference . RESULTS Of 302 subjects screened , 182 met criteria and were r and omized and 120 completed the study . There was a significant ( P<.05 ) dose-response relationship between amount of exercise and amount of weight loss and fat mass loss . The high-amount/vigorous-intensity group lost significantly more body mass ( in mean [ SD ] kilograms ) and fat mass ( in mean [ SD ] kilograms ) ( -2.9 [ 2.8 ] and -4.8 [ 3.0 ] , respectively ) than the low-amount/moderate-intensity group ( -0.9 [ 1.8 ] and -2.0 [ 2.6 ] , respectively ) , the low-amount/vigorous-intensity group ( -0.6 [ 2.0 ] and -2.5 [ 3.4 ] , respectively ) , and the controls ( + 1.0 [ 2.1 ] and + 0.4 [ 3.0 ] , respectively ) . Both low-amount groups had significantly greater improvements than controls but were not different from each other . Compared with controls , all exercise groups significantly decreased abdominal , minimal waist , and hip circumference measurements . There were no significant changes in dietary intake for any group . CONCLUSIONS In nondieting , overweight subjects , the controls gained weight , both low-amount exercise groups lost weight and fat , and the high-amount group lost more of each in a dose-response manner . These findings strongly suggest that , absent changes in diet , a higher amount of activity is necessary for weight maintenance and that the positive caloric imbalance observed in the overweight controls is small and can be reversed by a modest amount of exercise . Most individuals can accomplish this by walking 30 minutes every day Exercise is recommended by public health agencies for weight management ; however , the role of exercise is generally considered secondary to energy restriction . Few studies exist that have verified completion of exercise , measured the energy expenditure of exercise , and prescribed exercise with equivalent energy expenditure across individuals and genders . Objective The objective of this study was to evaluate aerobic exercise , without energy restriction , on weight loss in sedentary overweight and obese men and women . Design and Methods This investigation was a r and omized , controlled , efficacy trial in 141 overweight and obese participants ( body mass index , 31.0 ± 4.6 kg/m2 ; age 22.6 ± 3.9 years ) . Participants were r and omized ( 2:2:1 ratio ) to exercise at either 400 kcal/session or 600 kcal/session or to a non-exercise control . Exercise was supervised , 5 days/week , for 10 months . All participants were instructed to maintain usual ad libitum diets . Due to the efficacy design , completion of ≥ 90 % of exercise sessions was an a priori definition of per protocol , and these participants were included in the analysis . Results Weight loss from baseline to 10 months for the 400 and 600 kcal/session groups was 3.9 ± 4.9 kg ( 4.3 % ) and 5.2 ± 5.6 kg ( 5.7 % ) , respectively compared to weight gain for controls of 0.5 ± 3.5 kg ( 0.5 % ) ( p<0.05 ) . Differences for weight loss from baseline to 10 months between the exercise groups and differences between men and women within groups were not statistically significant . Conclusions Supervised exercise , with equivalent energy expenditure , results in clinical ly significant weight loss with no significant difference between men and women The acute ( single bout of exercise ) and chronic ( exercise training ) effects of exercise on plasma leptin were investigated in 97 sedentary adult men ( n = 51 ) and women ( n = 46 ) participating in the HERITAGE Family Study .  Exercise training consisted of a st and ardized 20-wk endurance training program performed in the laboratory on a computer-controlled cycle ergometer . Maximal oxygen uptake , body composition assessed by hydrostatic weighing , and fasting insulin level were also measured before and after training . Pre- and posttraining blood sample s were obtained before and after completion of a maximal exercise test on the cycle ergometer . Exercise training result ed in significant changes in maximal oxygen uptake ( increase in both genders ) and body composition ( reduction of fat mass in men and increase in fat-free mass in women ) . There were considerable interindividual differences in the leptin response to acute and chronic effects of exercise , some individuals showing either increase or reduction in leptin , others showing almost no change . On average , leptin levels were not acutely affected by exercise . After endurance training was completed , leptin levels decreased significantly in men ( from 4.6 to 3.9 ng/ml ; P = 0.004 ) but not in women . However , after the training-induced changes in body fat mass were accounted for , the effects of exercise training were no longer significant . Most of the variation observed in leptin levels after acute exercise or endurance training appears to be within the confidence intervals of the leptin assay . We conclude that there are no meaningful acute or chronic effects of exercise , independent of the amount of body fat , on leptin levels in humans OBJECTIVE To evaluate the relationship between changes in physical fitness and  risk of mortality in men . DESIGN Prospect i ve study , with two clinical examinations ( mean interval between examinations , 4.9 years ) to assess change or lack of change in physical fitness as associated with risk of mortality during follow-up after the subsequent examination ( mean follow-up from subsequent examination , 5.1 years ) . SETTING Preventive medicine clinic . STUDY PARTICIPANTS Participants were 9777 men given two preventive medical examinations  , each of which included assessment of physical fitness by maximal exercise tests and evaluation of health status . MAIN OUTCOME MEASURES All cause ( n = 223 ) and cardiovascular disease ( n = 87 ) mortality . RESULTS The highest age-adjusted all-cause death rate was observed in men who were unfit at both examinations ( 122.0/10,000 man-years ) ; the lowest death rate was in men who were physically fit at both examinations ( 39.6/10,000 man-years ) . Men who improved from unfit to fit between the first and subsequent examinations had an age-adjusted death rate of 67.7/10,000 man-years . This is a reduction in mortality risk of 44 % ( 95 % confidence interval , 25 % to 59 % ) relative to men who remained unfit at both examinations . Improvement in fitness was associated with lower death rates after adjusting for age , health status , and other risk factors of premature mortality . For each minute increase in maximal treadmill time between examinations , there was a corresponding 7.9 % ( P = .001 ) decrease in risk of mortality . Similar results were seen when the group was stratified by health status , and for cardiovascular disease mortality . CONCLUSIONS Men who maintained or improved adequate physical fitness were less likely to die from all causes and from cardiovascular disease during follow-up than persistently unfit men . Phys 
    Output:
    
We hypothesize that , when energy expenditure is equivalent , there will be no evidence for sex differences in body weight response to exercise