Background: Feelings of hunger and satiation are known to be influenced physiologically through hormone secretion. Ghrelin (GH) is known as the primary “hunger” hormone, and GLP-1, PP, PYY, and C-Peptide (CP) are hormones known to signal feelings of satiety. The aim of this study was to assess hunger and satiety hormone production during a prolonged fast, and to evaluate how an initial bout of exercise influences this secretion. Subjective feelings of mood and hunger were also assessed throughout.

Methods: In this crossover study, 20 adult subjects (11 Male, 9 Female) completed two 36-hour fasts, with one protocol requiring the subject to complete an intense treadmill exercise session at the beginning of the fast. Hunger and satiety hormone levels were assessed via venous blood samples taken every 12 hours. Subjective mood and hunger ratings were also recorded via an online survey every two hours.

Results: Compared with fasting only conditions, exercise conditions suppressed ghrelin secretion during the first 24 of the 36 hours of the fast (P = 0.01). Additionally, compared to fasting only conditions, hormone secretions of GLP-1 (P = .04) and C-peptide (P = .035) were significantly increased when compared to the fasting alone intervention between the initial measurements and at 12 and 24 hours after initiating the fast. However, subjective feelings of hunger and stomach discomfort did not differ between conditions.

Conclusions: Completing a bout of aerobic exercise at the beginning of a 36-hour fast results in significant decrease in ghrelin and significant increases in satiety hormone secretions while not making a significant impact on subjective ratings of hunger and stomach discomfort. Concentrations of hunger and satiety hormones provide evidence that an individual should feel less desire to consume food during a prolonged fast if they initiate that fast with a bout of aerobic exercise.



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