Meal Timing during Alternate Day Fasting: Effect on Body Weight and Cardiovascular Disease Risk

Background and aims: Alternate day fasting (ADF) involves the cycling between consuming 25% energy needs on the “fast day” with ad libitum intake on the “feed day”. It is effective for weight loss when the fast day meal is eaten at lunch. However, consuming this meal at a different time may optimize ADF for a broader group of dieters. Diet tolerability may be improved if this fast day meal was eaten at dinner or distributed throughout the day as small meals. Preliminary evidence suggests that ADF is safe; however, further investigation is warranted. Appetite alterations during ADF are not well understood. Accordingly, this study aimed to determine the optimal meal time and frequency of the fast day meal, evaluate the safety of this diet, and examine the effect of ADF on postprandial appetite ratings and gut peptides Methods: Obese subjects (n = 59) participated in an 8-week ADF study. Food was provided on the fast day. Results: All groups lost a similar amount of body weight, body fat, and visceral fat (P < 0.001). Plasma lipids were unaffected, and LDL particle size increased (P < 0.05) in all groups (1.3 ± 0.5 Å). Minor adverse events included constipation (17%), water retention (2%), dizziness (<20%), and general weakness (<15%). Depression and binge eating decreased (P < 0.01) after the diet. Purgative behavior and fear of fatness did not change. Subjects reported an improvement in (P < 0.01) restrictive eating and (P < 0.01) body image perception. Fasting leptin and insulin decreased (P < 0.05) and ghrelin AUC levels increased (P < 0.05). However hunger sensations were unchanged. PYY increased (P < 0.05) as did subjective fullness. Conclusion: Therefore, several ADF protocols are effective for weight loss and cardio-protections. Collectively, ADF appears to have minimal adverse effects and results in benign or beneficial alterations to psychological outcomes. Additionally, the appetite alterations stand to promote diet adherence due to an increase in fullness sensations without compensatory increases in hunger during weight loss.