Leptin, the product of ob gene secreted by adipose tissue as a hormone to regulate the deposition of body energy, has become a research focus of obesity problem during recent years. However, little is known concerning exercise and leptin. Therefore it is worth while to further study the effect of exercise on leptin level, especially the recommended aerobic exercise for weight control.
In this study, single acute aerobic stimulus composed by 30 min run-walk was applied to female subjects with different body compositions to examine the changes of leptin before and after the exercise, to analyze how the leptin response related to the cardiopulmonary endurance, total skinfold, waist to hip ratio, and tympanic temperature of the subjects, and to infer the possibility for a prediction formula. Seventy-two females were divided into three groups according to their body mass index (BMI): (1) the overweight (BMI >. 23), (2) the normal weight (19 < BMI < 23), and (3) the underweight (BMI ≦ 19). All the subjects completed breakfast at 8:00, then were undergone a thirty minutes run-walk stimulus during 9:00 to 11:00 in the morning. The intensity of the exercise was maintained at 50 ~ 85% maximal heart rate reserve (HRRmax). Blood samples were taken before and after the exercise from each individual, and analyzed for leptin concentration. The leptin level in the sera taken after the exercise was corrected by plasma volume to eliminate the effect of hemoconcentration caused by loss of water. All data were statistically analyzed by student t- test, Chi-square, one way ANOVA, regression and correlation analysis, and came to results as follows:
1. After exercise, the average leptin level of the overweight group was significantly elevated from 20.4 ±9.8 ng/ml to 24.2 ± 12.3 ng/ml (P < 0.001). For the normal weight group, leptin level also increased from 5.4 ±4.5 ng/ml to 6.3 ±5.3 ng/ml with significance (P < 0.001). There was no significant change in the leptin level for the underweight group (from 3.9 ±3.0 ng/ml to 4.0 ±3.7 ng/ml, P> 0.05).
2. The average leptin levels and the changes in it before and after exercise among three groups were significantly different (P < 0.0001) for showing the order of the overweight > the normal weight > the underweight.
3. The change in leptin levels was related to the BMI of the analyzed subjects. The regression analysis data showed that females with BMI larger than 18.8 tended to have a positive leptin response to the stimulus, and the degree of elevation was positively related to the BMI. On the contrary, subjects with BMI smaller than 18.8 tend to have a decreased leptin level after exercise, and the degree of decreasing was negatively related to the BMI. Using Chi-square analysis to evaluate the proportion of people that tend5 to have an increase or decrease in leptin level after exercise in each group has reached a meaningful result (P＝0.0009).
4. The leptin levels, no matter before or after the exercise, were significantly correlated to the cardiopulmonary endurance, total skinfold, waist to hip ratio, and tympanic temperature of the subjects (P < 0.05). The best one factor and two factors correlation formula for leptin concentration prediction before exercise were leptin conc, (ng/ml)=2.1601 x BMI (kg/m2) - 37.677, R2=0.7228, P < 0.0001, and leptin conc. (ng/ml)=1.7294 x BMI (kg/m2) - 0.0066 x 12''RW-13.571, R2=0.7980, P < 0.0001.
In conclusion, the effect of single acute 30 min run-walk exercise on the leptin level was different for subjects with different body composition. For women with larger BMI, exercise seemed to stimulate leptin level. As for underweight women, exercise caused a decrease in leptin level. Although cardiopulmonary endurance, total skinfold, waist to hip ratio, and tympanic temperature were also correlated to the level of leptin, BMI showed the best correlation.