The Effects of Fasting and Circadian Rhythms on Hunger and Mood: A Randomized Cross-over Study

Recent research highlights the role of circadian rhythms in regulating hunger and satiety. Preliminary evidence suggests that fasting earlier in the day may better align with circadian rhythms, potentially leading to lower hunger compared to later fasting windows. PURPOSE: This study aimed to explore the impact of different 24-hour fasting windows on subjective measures of hunger and mood. METHODS: A randomized crossover design was implemented with 24 participants (11 males, 13 females) with a BMI greater than 27. Each participant completed three 24-hour fasts, starting at either 8 am, 1 pm, or 6 pm, with a 5-day washout period between conditions. Subjective hunger and mood were assessed using a visual analog scale and the Brunel Mood Scale at multiple time points during the fast. RESULTS: There was a significant main effect of conditions for hunger (F = 6.76, P < 0.01) and tension (F = 4.74, P = 0.01). Participants reported greater hunger at the beginning and end of the evening fast, followed by the afternoon fast, and then the morning fast. More tension was reported at the beginning and end of the afternoon fast. There was a significant main effect of time for hunger (P < 0.01), stomach discomfort (P < 0.01), anger (P < 0.01), depression (P < 0.01), confusion (P = 0.02), and vigor (P < 0.01). Hunger, stomach discomfort, anger, depression and confusion went up during the fast while vigor went down. CONCLUSION: The timing of a 24-hour fast significantly influences subjective hunger and tension levels. Fasting in the evening may lead to higher hunger and tension, suggesting that morning fasts might be more manageable for individuals engaging in time restricted eating or intermittent fasting.