It can, based on the few controlled trials that exist. In a sleep-lab trial, adults on the same calorie-deficit diet lost the same weight with 5.5 or 8.5 hours in bed, but with the short nights they lost 55% less fat and 60% more fat-free mass1.
So the scale may not show it. What changes is what the weight is made of. This article walks through that trial, a longer one that followed, and what the evidence can and cannot say.
The terms
| Term | Plain meaning |
|---|---|
| Calorie deficit | Eating less energy than you use |
| Crossover trial | Every person tries both conditions, in random order |
| Fat-free mass | Everything in the body that is not fat: muscle, organs, water and bone |
| Time in bed | The window allowed for sleep; actual sleep is shorter |
The 2010 sleep-lab trial
The best-known study was run at a university sleep laboratory and published in the *Annals of Internal Medicine*1. Ten adults with overweight (three women, seven men, aged 35 to 49, sedentary non-smokers) completed it.
Each person did two 14-day stays in the lab, in random order, at least three months apart. The only planned difference was time in bed: 8.5 hours a night in one stay, 5.5 in the other1. Actual sleep averaged 7 hours 25 minutes against 5 hours 14 minutes.
The diet was fixed. Both stays used the same individual meals, set at 90% of each person's resting metabolic rate1. They ate about 1,450 kcal a day in both stays, while doubly labelled water (a tracer method that measures energy use over days) showed they used about 2,140 kcal a day. That is a deficit of roughly 690 kcal a day, or about a third of their energy use, by our arithmetic.
For comparison, Zyra's calorie calculator caps a deficit at 35% of TDEE (total daily energy expenditure) and never sets a target below a floor of 1,500 kcal for men or 1,200 kcal for women on its standard setting (see how big should a calorie deficit be). The trial's diet was a supervised research protocol, not a template.
In plain terms: same people, same food, same deficit. Only the nights changed.
What the trial found
The scale did not tell them apart. Weight loss was about the same: 2.9 kg with long nights and 3.0 kg with short nights, as group averages1.
What was lost did differ. With long nights the group lost 1.4 kg of fat on average; with short nights, 0.6 kg. The paper expresses it as a 55% drop in the share of weight lost as fat. Fat-free mass went the other way: 1.5 kg lost with long nights against 2.4 kg with short nights, 60% more1.
What was lost in 14 days: 8.5 vs 5.5 hours in bed · kg (group average)
8.5 h in bed 5.5 h in bed
Put as shares, fat made up about 56% of the weight lost with 8.5 hours in bed and only about 25% with 5.5 hours1.
Share of the weight lost that was fat · %
They were hungrier. Hunger ratings before meals rose more during the short-sleep stay1. Because food was fixed, extra hunger could not change what they ate here. The authors suggest that outside a lab it could make a diet harder to stick to; the trial did not test that.
The authors concluded that sleep "contributes to the maintenance of fat-free body mass at times of decreased energy intake" and that lack of sleep "may compromise the efficacy of typical dietary interventions"1.
In plain terms: on short sleep, the same diet took off less fat and more of everything else.
A longer trial, outside the lab
A 2018 trial tested a milder version for eight weeks2. Thirty-six adults with overweight or obesity were told to eat at 95% of their measured resting metabolic rate. Twenty-one were also asked to cut time in bed on five nights a week and sleep freely on the other two. They slept about 57 minutes less on restricted nights and about 59 minutes more on free nights, a net loss of about 169 minutes a week.
The two groups lost similar amounts of weight, lean mass and fat mass. But the share of weight lost as fat was significantly greater in the group that slept normally2. The authors concluded that about an hour less sleep on five nights a week led to a smaller share of fat loss, and that "catch-up" sleep on the other nights may not fully offset it.
The other direction: more sleep
A 2022 trial asked whether extending sleep changes how much people eat3. Eighty adults with overweight who habitually slept less than 6.5 hours were randomised to a single sleep-hygiene counselling session aimed at 8.5 hours in bed, or to carry on as usual, at home and with no diet prescribed. The counselled group slept about 1.2 hours more a night. Measured with doubly labelled water and body composition scans, their energy intake fell by about 270 kcal a day compared with the control group (95% CI 147 to 393 kcal)3.
That trial looked at energy intake, not a planned diet. It suggests that short sleep may act on the eating side as well as on body composition, but it tested a different question.
What this does and does not mean
It does not mean sleep makes you lose fat. No study here showed sleep on its own causing fat loss. In the 2010 and 2018 trials, everyone was in a deficit; sleep changed what the loss was made of12.
It does not mean short sleep adds fat. The 2010 trial fixed food, so it cannot speak to weight gain.
It does suggest the scale can mislead. If sleep changes the mix of fat and fat-free mass lost, weight alone will not show it (see why the scale doesn't match the mirror and trend weight vs scale weight).
Fat-free mass is not all muscle. It includes water, organs and bone. The trial measured fat-free mass as weight minus fat, not muscle directly, so it does not show how much muscle was lost.
For individual questions about sleep, a doctor is the right person to ask. This page describes what the trials found in groups; it is not a sleep or nutrition prescription.
What the studies found
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Nedeltcheva et al., *Ann Intern Med*1 | 10 adults with overweight; 14 days in a sleep lab, twice | Same weight loss; share lost as fat 55% lower and 60% more fat-free mass lost with 5.5 vs 8.5 h in bed | 2010 |
| Wang et al., *Sleep*2 | 36 adults with overweight or obesity; 8 weeks | Similar weight loss; smaller share lost as fat with about 1 h less sleep on 5 nights a week | 2018 |
| Tasali et al., *JAMA Intern Med*3 | 80 short-sleeping adults with overweight, at home | Sleep extension: about 270 kcal a day lower energy intake vs control | 2022 |
| Duan et al., *Obes Rev*4 | 30 studies, 10,944 participants | Mixed overall; sleep restriction studies suggested less fat loss | 2026 |
Limits worth knowing
- Tiny and short. The 2010 trial had 10 people over two 14-day stays; the authors note that "the nature of the study limited its duration and sample size"1.
- Lab conditions. Fixed food, sedentary volunteers and supervised nights are not everyday life.
- Body composition is hard to measure precisely over two weeks, and fat-free mass includes water.
- Two people did not finish. Of 12 enrolled in 2010, one stopped after palpitations during combined calorie and sleep restriction and one left for a new job1.
- Abstracts only for the 2018, 2022 and 2026 studies.
- Funding. The 2010 trial was supported by US National Institutes of Health grants1.
Latest research
The newest work we opened is a 2026 systematic review of 30 studies with 10,944 participants on sleep and weight-loss programmes in adults with excess weight4. It found the overall evidence mixed: studies that deliberately restricted sleep suggested less fat loss, while observational links between sleep duration and weight loss were inconsistent. The authors call for high-quality experimental studies to clarify cause.
The short version
- In a controlled trial, short nights did not change how much weight came off during a diet.
- They did change what came off: 55% less fat and 60% more fat-free mass.
- A longer trial with milder sleep loss found a similar shift in the share lost as fat.
- The evidence is small and short-term; the scale alone would not have shown the difference.
Educational overview only — not medical advice.
