Sleep and fasting

Sleep and fasting are closely linked. Most of your fast happens while you sleep, so a good night makes the whole thing easier. And a bad night does the opposite: it turns up your hunger the next day, and makes it harder to stick to your plan. Here's what studies show, and some simple ways to make your fasting window and your sleep work together.

Short sleep makes you hungrier

Your appetite is controlled partly by two hormones: ghrelin, which makes you hungry, and leptin, which helps you feel satisfied. Sleep affects both. In a carefully controlled study, healthy young men had their sleep cut short for two nights, and on another occasion were given two nights of extra sleep. They ate the same food both times. After the short nights, their leptin was lower, their ghrelin was higher, and they were noticeably hungrier, especially for sweet and starchy foods ¹.

Does fasting affect your sleep?

Some people worry that going to bed with an emptier stomach will keep them awake. The research so far is reassuring. A review of randomized trials of time-restricted eating lasting at least 8 weeks found that it doesn't typically worsen sleep, although a few studies saw small changes in one direction or the other ³. A larger 2025 analysis of 18 trials in adults with overweight found no overall effect of intermittent fasting on sleep quality ⁴.

Time your last meal, coffee and drink

Going to bed on a very full stomach can disturb your night in a different way. In a Japanese study, people who went to bed less than 3 hours after dinner had about seven times the odds of reflux compared with those who waited 4 hours or more ⁶. It was an observational study, so it can't prove cause and effect, but it fits with what many doctors advise. Closing your eating window a few hours before bed is one of the easiest ways to combine fasting with better nights.

Sources

1. Spiegel K, Tasali E, Penev P, et al. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med. 2004;141(11):846-50. doi.org/10.7326/0003-4819-141-11-200412070-00008
2. Al Khatib HK, Harding SV, Darzi J, et al. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. Eur J Clin Nutr. 2017;71(5):614-624. doi.org/10.1038/ejcn.2016.201
3. Bohlman C, McLaren C, Ezzati A, et al. The effects of time-restricted eating on sleep in adults: a systematic review of randomized controlled trials. Front Nutr. 2024;11:1419811. doi.org/10.3389/fnut.2024.1419811
4. Yong YN, McCubbin AJ, O'Driscoll DM, et al. The effects of intermittent fasting on sleep quality and cardiometabolic health outcomes in adults with overweight/obesity status: a systematic review and meta-analysis of randomized controlled trials. Sleep Med Rev. 2025;84:102193. doi.org/10.1016/j.smrv.2025.102193
5. Clavero-Jimeno A, Dote-Montero M, Migueles JH, et al. Time-Restricted Eating and Sleep, Mood, and Quality of Life in Adults With Overweight or Obesity: A Secondary Analysis of a Randomized Clinical Trial. JAMA Netw Open. 2025;8(6):e2517268. doi.org/10.1001/jamanetworkopen.2025.17268
6. Fujiwara Y, Machida A, Watanabe Y, et al. Association between dinner-to-bed time and gastro-esophageal reflux disease. Am J Gastroenterol. 2005;100(12):2633-6. doi.org/10.1111/j.1572-0241.2005.00354.x