Appetite regulation in humans: effect of sex hormones and exercise intensity

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The idea that exercise may produce fat loss without dietary intervention is controversial, as aerobic exercise alone frequently results in fat loss in males but is less effective in females. Recently, we demonstrated an intense model of high-intensity interval training (HIIT) known as sprint interval training (SIT; 4-6 repeated “all-out” 30 s efforts separated by 4 min active rest) induced fat loss in both males and females. However, the magnitude of the fat loss was greater in males. To explore the mechanism for the ability of interval training to induce fat loss, we measured post-exercise metabolism over 24 h across three experimental sessions (no exercise, SIT, moderate-intensity aerobic exercise). Despite the drastically reduced exercise volume (2 min of exercise SIT vs 30 min aerobic), SIT induced a small but prolonged increase in post-exercise metabolism, which likely contributes to the SIT-induced fat loss. However, this increase in post-exercise metabolism is similar across sex. This suggests sex hormones and exercise intensity affect appetite-regulation. Appetite regulation involves the integration of the appetite-stimulating (ghrelin) and appetite-inhibiting (PYY, GLP-1) hormones in the brain, which acutely regulate energy intake. While eating and fasting are known to influence these signals, the mechanisms by which sex hormones and exercise affect appetite-regulation are unknown. Thus, the long-term goal of this research program is to improve our understanding of the specific mechanisms responsible for human appetite regulation. As estrogen and progesterone are known to influence energy intake, sex differences likely involve these key sex hormones. Further, while research has demonstrated exercise alters energy intake, the mechanisms responsible remain unclear. The short-term objectives will explore how: 1) sex hormone levels (estrogen, progesterone) during the menstrual cycle affect appetite-regulating hormones; and 2) how the intensity of exercise alters the appetite-regulating hormones due to increases in the skeletal muscle inflammatory marker interleukin-6 (IL-6) and 3) blood lactate (product of muscle metabolism). The proposed work will be conducted in humans using serial blood draws (fasted, fed, pre- and post-exercise) over several hours to establish a time course of effects. Specific appetite-regulating hormones (grehlin, PYY, GLP-1) and potential physiological mediators (sex hormones, IL-6, lactate) will be analyzed. This research will improve our understanding of appetite regulation and provide training of numerous highly qualified personnel in exercise physiology, endocrinology, and fitness evaluation/exercise prescription. The long-term impact of this research will provide new insights on appetite regulation to improve strategies to induce body fat loss aiding the treatment of metabolic disorders such as obesity and type II diabetes.