Fasting diets leave sleep largely untouched

Intermittent fasting has become a mainstream weight-loss tool for people with overweight or obesity, with alternate-day fasting, time-restricted eating and the 5:2 diet the three dominant styles. A common worry is that going long stretches without food, or eating on an unusual schedule, might disturb sleep, and poor sleep would be a heavy price for weight loss. Yet the effects of fasting on sleep have remained unclear, with individual trials too small to settle it. This analysis pooled the randomised evidence to compare fasting styles, continuous calorie restriction and usual diets on sleep outcomes.

The researchers searched multiple databases in January 2025 for randomised controlled trials in adults with overweight or obesity that compared intermittent fasting, continuous energy restriction and a usual diet on sleep-related outcomes. Sixteen trials qualified. The primary outcome was the global Pittsburgh Sleep Quality Index, a standard questionnaire score, with secondary outcomes including its components, the Epworth sleepiness scale and other subjective and objective sleep measures. A Bayesian network meta-analysis allowed all the diet approaches to be compared against each other simultaneously.

There were no significant differences in Pittsburgh Sleep Quality Index components among alternate-day fasting, continuous energy restriction, time-restricted eating, the 5:2 diet and a usual diet. A few small signals did emerge: alternate-day fasting scored worse on sleep latency than both continuous restriction and a usual diet, with differences of 1.04 and 1.39 points on that component. Time-restricted eating was associated with longer time in bed than a usual diet and a longer sleep onset latency than continuous restriction, differences of 26.04 and 9.54 on those measures. Most other sleep parameters showed no differences at all.

This is a broadly reassuring answer to a reasonable worry, and it fits the wider picture that fasting's main effects show up in weight and metabolic markers rather than sleep. The slight delays in falling asleep with alternate-day fasting and time-restricted eating are worth noting but small, and the authors caution that the included trials were small with varying protocols. Whether specific eating windows, for example early versus late in the day, matter for sleep remains an open question these pooled comparisons cannot resolve.

If sleep worries have kept you away from fasting-style diets, this evidence suggests the fear is mostly unfounded: across 16 trials, overall sleep quality held steady regardless of the eating pattern. The small delays in falling asleep seen with alternate-day fasting and time-restricted eating are the one thing to watch, particularly if drifting off is already a struggle. None of this makes fasting better or worse for weight loss, it simply removes sleep from the list of likely casualties. Firmer answers await larger, better standardised trials.