In 30 seconds
- On the same diet, spending 5.5 hours in bed instead of 8.5 reduced the fat lost by 55% and increased the fat-free mass lost by 60%.
- After short sleep, people ate an average of 385 kcal more a day, in a meta-analysis of 11 studies, with no rise in energy expenditure.
- In adults with overweight who slept less than 6.5 hours, extending sleep by 1.2 hours reduced what they ate by 270 kcal a day.
- On a 15-24 week diet, each extra hour of sleep was associated with 0.72 kg more fat lost.
Short sleep does not stop you losing weight, but it changes what you lose. On the same diet, people who slept 5.5 hours instead of 8.5 lost 55% less fat and more lean mass 2. On top of that, short sleep makes you eat more: around 385 kcal a day on average 5.
Hours of sleep per night
How much sleep an adult needs
Why sleep belongs in your plan
When you diet, what you are after is losing fat and keeping your muscle. Studies show that sleep influences both, and the hunger you feel along the way.
It is the piece most often forgotten. The sleep experts' recommendation is clear: adults need 7 hours or more a night, and 6 or fewer are not enough to maintain health 1.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Fat lost on a diet | Moderate | Less fat and more lean mass lost with short sleep in two trials, with the same weight lost. |
| Hunger and calories | Moderate | 385 kcal more a day after short sleep, in a meta-analysis of 11 studies. |
| Appetite hormones | Moderate | Less leptin and more ghrelin with fewer hours of sleep, in a cohort of 1,024 adults and in trials. |
| Sleeping more to eat less | Preliminary | 270 kcal less a day by extending sleep by 1.2 hours, in a trial with 80 adults. |
| Catching up on sleep at the weekend | Preliminary | Sleeping more on 2 nights did not fully make up for 5 short nights in an 8-week trial. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Nedeltcheva et al., 2010 | Crossover trial | 10 adults with overweight, average age 41 | 14 days on the same diet: 1.4 kg of fat lost with 8.5 hours in bed, compared with 0.6 kg with 5.5. Fat-free mass lost: 1.5 compared with 2.4 kg. 2 |
| Wang et al., 2018 | Randomised trial | 36 adults with overweight or obesity | 8 weeks of dieting with one hour less sleep 5 nights a week: same weight lost, but a smaller proportion of fat. 3 |
| Chaput and Tremblay, 2012 | Intervention study | 123 adults with overweight or obesity | Diet of 600-700 kcal less for 15-24 weeks: 0.72 kg more fat lost for each extra hour of sleep. 4 |
| Al Khatib et al., 2017 | Meta-analysis | 11 studies, 172 people | After short sleep, 385 kcal more a day, with no change in energy expenditure. 5 |
| Taheri et al., 2004 | Cohort | 1,024 adults | Sleeping 5 hours compared with 8: 15.5% less leptin, 14.9% more ghrelin and a higher BMI. 6 |
| Tasali et al., 2022 | Randomised trial | 80 adults with overweight | Extending sleep by 1.2 hours a night for 2 weeks: 270 kcal less a day, without counting calories. 7 |
Same diet, 14 days
5.5 hours in bed instead of 8.5
The landmark trial: same diet, different sleep
In 2010, 10 adults with overweight and an average age of 41 followed the same diet twice, for 14 days each time. They ate 90% of what they used at rest. The only thing that changed was time in bed: 8.5 hours in one phase and 5.5 hours in the other 2.
| 8.5 hours in bed | 5.5 hours in bed | |
|---|---|---|
| Actual sleep | 7 h 25 min | 5 h 14 min |
| Weight lost | 2.9 kg | 3.0 kg |
| Fat lost | 1.4 kg | 0.6 kg |
| Fat-free mass lost | 1.5 kg | 2.4 kg |
| Share of weight lost that was fat | 56% | 25% |
Source: Nedeltcheva et al., 2010. 10 adults with an average age of 41, eating 90% of their resting energy expenditure in both phases.
They lost almost the same weight. But with short sleep, only a quarter of what they lost was fat; the rest came mainly from fat-free mass 2.
There were more changes with short sleep 2:
- More hunger and more ghrelin, the hormone that triggers it.
- Lower resting energy expenditure: around 147 kcal less a day.
- Less fat used for energy, both fasted and after meals.
One hour less on weekdays
Real life looks more like this: an hour less sleep during the week and a bit more at the weekend. A trial tested it with 36 adults with overweight or obesity over 8 weeks of dieting 3.
One group slept as usual. The other cut their time in bed on 5 nights a week, by about 57 minutes, and slept as much as they wanted on the other 2 3.
Both groups lost a similar amount of weight. But in the group that cut back on sleep, the share of weight lost that was fat was significantly smaller. The authors believe that catching up at the weekend does not fully make up for it 3.
Every hour counts
One study followed 123 adults with overweight or obesity on a diet of 600-700 kcal less a day, for 15 to 24 weeks. They lost 4.5 kg on average, 76% of it fat 4.
The researchers adjusted for age, sex, starting weight and what people ate. Even so, each extra hour of sleep was associated with 0.72 kg more fat lost. People who slept better at the start also lost more fat 4.
Sleep and hunger
Short sleep versus more sleep
Short sleep makes you eat more
A meta-analysis of 11 studies with 172 people compared short nights with normal nights. After short sleep, people ate 385 kcal more a day, with more fat and less protein, and energy expenditure did not change 5.
Appetite hormones help to explain it. In a cohort of 1,024 adults, sleeping 5 hours instead of 8 was associated with 15.5% less leptin, which makes you feel full. And with 14.9% more ghrelin, which triggers hunger. Those who slept less had a higher BMI 6.
Sleep more, eat less
It also works the other way round. A trial tested it with 80 adults with overweight who slept less than 6.5 hours. The group that extended their sleep by 1.2 hours a night for 2 weeks ate 270 kcal less a day 7.
They were not counting calories or dieting: they ate what they wanted in their normal lives. Some cut their intake by as much as 500 kcal a day 7.
How to protect your sleep during a fat-loss phase
- Set aside time in bed. If you need 7-8 hours of sleep, allow a little more time in bed: in the landmark trial, 8.5 hours in bed gave 7 h 25 min of actual sleep 2.
- A regular schedule, at the weekend too: catching up on hours does not fully make up for it 3.
- Watch your afternoon caffeine. We explain why in caffeine and sleep.
- Do not cut your dinner so much that you go to bed hungry: the deficit is measured at the end of the day.
- Evening routine: low light, screens out of bed and a cool bedroom. You have it step by step in the sleep and recovery guide.
If you are not sure how well you are sleeping, start with our sleep test.
What about CLA?
With your sleep, diet and training in order, CLA has also been studied. In a meta-analysis of 18 trials, 3.2 g a day led to 0.09 kg more fat lost per week than placebo 8.
You have the full plan in the fat-loss guide.
Frequently asked questions
Does lack of sleep make you put on weight?
It can make things harder for you. In a meta-analysis of 11 studies, after short sleep people ate an average of 385 kcal more a day, without using more energy. And in a cohort of 1,024 adults, sleeping less was associated with a higher BMI.
How many hours of sleep do you need to lose fat?
Sleep experts recommend 7 hours or more for adults. In the landmark trial, people who spent 8.5 hours in bed lost more than twice as much fat as with 5.5 hours, on the same diet.
Can you catch up on sleep at the weekend?
Only partly. In an 8-week trial, sleeping one hour less on 5 nights and one hour more on the other 2 led to less fat being lost than sleeping normally all week.
Why am I hungrier when I sleep badly?
Because your appetite hormones change. With 5 hours of sleep compared with 8, researchers measured 15.5% less leptin, which makes you feel full, and 14.9% more ghrelin, which makes you hungry.
Sources
- Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843-844. View publication
- Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435-441. View publication
- Wang X, Sparks JR, Bowyer KP, Youngstedt SD. Influence of sleep restriction on weight loss outcomes associated with caloric restriction. Sleep. 2018;41(5):zsy027. Europe PMC record. View publication
- Chaput JP, Tremblay A. Sleeping habits predict the magnitude of fat loss in adults exposed to moderate caloric restriction. Obes Facts. 2012;5(4):561-566. View publication
- Al Khatib HK, Harding SV, Darzi J, Pot GK. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. Eur J Clin Nutr. 2017;71(5):614-624. View publication
- Taheri S, Lin L, Austin D, Young T, Mignot E. Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index. PLoS Med. 2004;1(3):e62. View publication
- Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. Effect of sleep extension on objectively assessed energy intake among adults with overweight in real-life settings: a randomized clinical trial. JAMA Intern Med. 2022;182(4):365-374. View publication
- Whigham LD, Watras AC, Schoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203-1211. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
