Does sleep affect weight loss? (Research Review)

Written by: Jack Quint | Graphics and editing : Adam Tzur | Published: September 30, 2021 1Updated October 4, 2021

Key takeaways

Research suggests that...

  1. Sleep recovers your body and mind. Hormones are key to this regeneration.
  2. Sleep deprivation will put your body in a catabolic state. This means you may gain fat and lose muscle mass.
  3. If you are on a diet, sleep longer to speed up weight loss and prevent muscle loss.

The full science-based article continues below the infographic.

What Happens When We Sleep

Outside of training and nutrition, recovery should be your top priority for building muscle, gaining strength, or losing body fat.

Getting adequate sleep at night is essential for recovery from both a performance and health perspective. In this article, we’ll show you the scientific data on sleep duration and body composition.

Sleep Stages And Sleep Cycles

There are two primary types of sleep: rapid eye movement (REM) and non rapid eye movement (non-REM). While REM is just a single sleep stage, non-REM contains three stages- each of which have their own specific functions towards recovery.

Here’s a brief summary of each of the four sleep stages from sleep onset to deep sleep [49].

  • Stage 1 (non-REM): this happens during the first few minutes of falling asleep. Heart rate and breathing begin to slow down.
  • Stage 2 (non-REM): a period of light sleep before you enter deep sleep, typically lasting for around 25 minutes of the sleep cycle.
  • Stage 3 (non-REM): the slow-wave deepest sleep cycles. It is during this time that the greatest amount of recovery and regeneration takes place, leaving you refreshed in the morning.
  • Stage 4 (REM): the final stage of sleep. Eye movement and brain activity significantly increase, and this is when most dreams will occur.

Combined, these stages make up one sleep cycle. This cycle repeats itself throughout the night and lasts approximately 90 minutes each time.

How sleep helps the body recover

Getting a good night of sleep helps us feel refreshed and recovered in the morning, and that doesn’t just happen magically. During each sleep cycle, a variety of biological processes take place that support our health.

Here are some key processes that happen overnight [48]:

  • Cellular and tissue restoration: throughout the day, we perform a wide variety of activities that stresses our body. During sleep, muscles and tissues are repaired.
  • Improved brain function: sleep clears out waste and improves cognitive function. Sleep deprivation can negatively affect learning and memory.
  • Energy conservation: when we sleep, we greatly reduce our energy expenditure. At the same time, we are not consuming energy, leaving us at a relative energy balance. This helps facilitate recovery and allows us to save our energy for when we need it during the day.

The role of hormones

Sleep is a crucial time for the release of hormones in the body. Many of these hormones are responsible for aiding in muscle repair, the regulation of appetite, or neurotransmitters that influence mood and stress levels.

Some of the most important ones are described below.

How Poor Sleep Affects Weight Loss

Now that we have discussed a thorough background on the different sleep cycles and processes that occur overnight, we can dive into the main topic of this article: how exactly does sleep duration affect fat loss?

Sleep deprivation slows fat loss and burns muscle instead

We found that sleep restriction resulted in less loss of fat but greater loss of lean mass (...). - Wang et al. 2018 (23)


Two studies have looked at the effects of sleep restriction in an energy deficit on body composition (fat mass and fat-free mass) in adults [24; 23]. In these studies, all participants lost body weight. However, the sleep deprived participants lost more fat-free mass (i.e muscle and water).

There are several potential reasons for this muscle loss [29, 55, 56, 57].

When sleep deprived,

  • the body produces more cortisol and less testosterone,
  • muscle protein synthesis goes down, and
  • muscle protein breakdown may go up

A single night of total sleep deprivation is sufficient to induce anabolic resistance (...) - Lamon et al., 2021 (56)

Hence, sleep deprivation is catabolic.

Finally, a 2015 meta-analysis examined the impact of sleep duration on body mass. The researchers found that restricting sleep led to either more weight gained or less weight lost, although it was not a statistically significant effect [6].

If you have physique goals, this is not good. You want to maintain as much muscle mass as possible during a diet, while burning as much fat as possible.

Lack of sleep makes you eat more and move less

The basics of energy balance

Energy balance is how many calories you eat minus the calories you burn. This is also known as Calories In, Calories Out (CICO).

If you are eating more calories than you burn, then you will gain weight. If you expend more calories than you eat, you will lose weight.

Factors that affect calories in:

  • Hormones
  • Hunger
  • How much food you eat
  • Calories absorbed

Factors that affect calories out:

  • Calories burned at rest (basal metabolic rate)
  • Calories burned during exercise
  • Calories burned outside of exercise (i.e. leisure activities)
  • Calories burned when metabolizing food

Sleep affects energy balance

Overall, sleep restriction makes you more passive, thus expending less energy.

There are multiple lines of evidence that suggests that sleep restriction has a negative effect on energy expenditure. First, sleep restriction may reduce energy expenditure by decreasing physical activity due to tiredness and fatigue. In a crossover study on healthy adults, subjects had either a regular 24 hour sleep-wake cycle or a 24 hour period of complete wakefulness [2].

The researchers found that after a night of complete sleep restriction, subjects recorded a reduced resting and postprandial energy expenditure of 5% and 20%, respectively [2].

Other studies have found that sleep loss is associated with fatigue that results in not only less physical activity, but also less non-exercise activity thermogenesis, which has shown to have a profound effect on an individual’s daily energy expenditure [31].

It’s important to note though that not all studies find that sleep restriction has a profound effect on energy expenditure.

For example, in a 2010 randomized crossover study, 12 healthy men were restricted to either 4 or 8 hours a sleep [1]. Interestingly, physical activity was higher for the sleep-restricted group, even though their sleepiness was higher [1].

Some researchers have concluded that energy expenditure is not the primary component linking sleep deprivation to excess body fat, and is rather influenced by increased hunger and calorie intake [29; 31].


Sleeping Longer Speeds Up Weight Loss

Sleep extension favors weight loss in adolescents under caloric restriction (...) - Moreno-Frias et al., 2020 (41)

The current evidence suggests that increasing sleep duration and quality is beneficial for losing body fat. This might be because you are less likely to overeat, the longer you sleep [43].

Three studies have found that sleeping longer is associated with reduced fat mass (54, 43, 41).

Chaput (43) found that sleeping 1 hour longer was associated with a 0.7 kg decrease in fat mass. In Jåbekk (54), participants who trained and got sleep education lost 1.8 kg of fat. The control group who only trained without sleep education, did not lose fat.

Another study looked at the effects of sleep extension on body composition and metabolic conditions in obese adolescents [41]. 52 subjects received a diet with daily 500 calorie restriction, and were randomly assigned to either a sleep extension or control group. The sleep extension group aimed to increase their sleep by a total of 1 hour per night.

The researchers found that both groups lost weight, but the sleep-extension group improved weight loss and waist circumference to a significantly greater extent. Additionally, sleep extension improved inflammation and other metabolic conditions [41].

Collectively, these studies provide evidence that sleep extension may aid fat loss.


Methodology and Study Quality

Our Systematic Search Strategy

We researched sleep and fat loss using the Europe PMC database.

We used the following search string: (“sleep”) AND ("calorie restriction" OR "caloric restriction" OR "diet" OR "caloric deficit") AND (“fat mass” OR “body fat” OR “adipose tissue” OR “fat tissue” OR "weight loss") NOT ("disease" OR "cancer" OR "pain" OR "ventricular" OR "alcohol" OR "covid" OR "rat" OR "mouse" OR "mice" OR "animal" OR "insect" OR "patient").

Date range: we included all studies that were published up until 17.05.2021.

We reviewed the references of included studies to identify more studies. Additional studies were found in the “similar articles” section on the journal websites.

Study Outcomes

The primary outcomes we assessed from the available studies were the effect of sleep duration on fat mass, body mass, or BMI.

Our secondary outcomes included the effect of sleep duration on hormonal secretion, metabolism, energy expenditure, and appetite/calorie consumption.

Inclusion Criteria

Studies that were included in our analysis had to meet all of the following criteria:

  1. Were carried out in humans
  2. Subjects ranged in age from 18 years or older
  3. Was a narrative or systematic review analyzing sleep parameters on weight loss or body composition
  4. Assessed any of the primary or secondary outcomes

Exclusion Criteria

Additionally, studies from our systematic search were excluded for any of the following reasons:

  1. Consisted of animal, in vitro, disease or case studies
  2. Had fewer than 10 participants
  3. For experimental trials investigating primary outcomes: duration shorter than 2 weeks

Study Inclusion And Data Extraction

The systematic search yielded 673 studies. 29 studies were included after first-pass inclusion. These studies were scanned and 17 additional studies were extracted from the references. A second-pass exclusion was performed and 3 studies were removed.

This left us with a grand total of 43 included studies for the review. 6 additional references were included for other sections of the article.

The Strengths Of The Literature

Study length

One of the advantages of observational studies is that they are able to assess individuals over different time periods. Many of the studies in our review were several months long, sometimes upwards of multiple years. When we are able to assess longitudinal changes in a given variable over time, we can have more confidence in the data.

Strong mechanistic rationale

Although there aren’t many RCT’s looking at the effects of different sleep durations on body composition, many published studies have demonstrated mechanistically why sleep restriction likely limits fat loss. This includes many of the secondary outcomes we assessed in our review: decreased energy expenditure, increased appetite/food consumption, and altered hormones/metabolism.

Large sample sizes

Many studies in our review report findings from several hundred or thousands of participants, which can increase our confidence and the ecological validity of these findings. Larger sample sizes provide a smaller margin error by limiting the effects of outliers in a given investigation.

The Most Common Study Limitations

Study designs

Although observational and cross-sectional studies can enroll a large number of participants, their main flaw is that they cannot establish cause-and-effect between variables, and rather can observe general trends and relationships. To further investigate a causative relationship between sleep duration and fat loss, we’ll need additional randomized controlled trials, and eventually meta-analyses.

Lack of exercise or nutrition intervention

We’ve seen in thousands of studies over the years that exercise and nutrition can have a profound effect on body composition. Specifically, the inclusion of resistance training and an elevated protein intake have shown to help maintain FFM during an energy deficit. Future studies looking at the effect of sleep duration on multiple compartments of body composition (i.e. fat mass and fat-free mass) should aim to include an exercise and nutrition protocol to stimulate FFM retention.

Body composition measurements

Within the RCTs that we have which have measured body composition during a sleep  intervention, body composition measurements are often assessed using a 2-compartment (fat mass and fat-free mass or 3-compartment (fat mass, bone mineral, other fat-free mass). Additionally, body composition is typically assessed with DEXA. Even though this is considered the “gold standard” body composition method, fat-free mass is largely confounded by hydration status. This means that it is not the ideal measure of skeletal muscle mass, compared to a validated method like ultrasound or MRI.


Systematically collected studies

Citation number Study title First author and year
1 Acute partial sleep deprivation increases food intake in healthy men Brondel, 2010
2 Acute sleep deprivation reduces energy expenditure in healthy men Benedict, 2011
3 Assessment of sleep and obesity in adults and children: Observational study. Bonanno, 2019
4 Associations between Poor Sleep Quality, Obesity, and the Anthropometric Measurements of Women in Turkey. Ozturk, 2018
5 Associations of disordered sleep with body fat distribution, physical activity and diet among overweight middle-aged men. Tan, 2015
6 A Systematic Review and Meta-Analysis of Randomized Controlled Trials of the Impact of Sleep Duration on Adiposity and Components of Energy Balance Capers, 2015
7 Behavioural mediators of reduced energy intake in a physical activity, diet, and sleep behaviour weight loss intervention in adults. Fenton, 2021
8 Beneficial Impact of Sleep Extension on Fasting Insulin Sensitivity in Adults with Habitual Sleep Restriction Leproult, 2015
9 Brief communication: sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite Spiegel, 2004
10 Concomitant changes in sleep duration and body weight and body composition during weight loss and 3-mo weight maintenance. Verhoef, 2013
11 Does stress influence sleep patterns, food intake, weight gain, abdominal obesity and weight loss interventions and vice versa? Geiker, 2018
12 Eating behavior traits and sleep as determinants of weight loss in overweight and obese adults. Filiatrault, 2014
13 Effect of shortened sleep on energy expenditure, core body temperature, and appetite: a human randomised crossover trial Hibi, 2017
14 Effects of experimental sleep restriction on caloric intake and activity energy expenditure Calvin, 2013
15 Effects of experimental sleep restriction on weight gain, caloric intake, and meal timing in healthy adults Spaeth, 2013
16 Effects of recovery sleep after one work week of mild sleep restriction on interleukin-6 and cortisol secretion and daytime sleepiness and performance. Pejovic, 2013
17 Energy expenditure during sleep, sleep deprivation and sleep following sleep deprivation in adult humans Jung, 2011
18 Experimental sleep curtailment causes wake-dependent increases in 24-h energy expenditure as measured by whole-room indirect calorimetry Shechter, 2013
19 Exposure to recurrent sleep restriction in the setting of high caloric intake and physical inactivity results in increased insulin resistance and reduced glucose tolerance. Nedeltchva, 2009
20 Factors that may impede the weight loss response to exercise-based interventions. Boutcher, 2009
21 Habitual sleep variability, not sleep duration, is associated with caloric intake in adolescents. He, 2015
22 Impact of sleep debt on metabolic and endocrine function Spiegel, 1999
23 Influence of sleep restriction on weight loss outcomes associated with caloric restriction. Wang, 2018
24 Insufficient sleep undermines dietary efforts to reduce adiposity Nedeltchva, 2010
25 Less physical activity and more varied and disrupted sleep is associated with a less favorable metabolic profile in adolescents. Rognvaldsdottir, 2020
26 Longer sleep duration associates with lower adiposity gain in adult short sleepers Chaput, 2011
27 Longitudinal associations between sleep duration and subsequent weight gain: A systematic review Magee, 2012
28 Obesity and sleep disturbance: the chicken or the egg? Muscogiuri, 2019
29 Partial sleep deprivation and energy balance in adults: an emerging issue for consideration by dietetics practitioners. Shlisky, 2012
30 Relationship between sleep pattern and efficacy of calorie-restricted Mediterranean diet in overweight/obese subjects. Pagliai, 2018
31 Role of sleep duration in the regulation of glucose metabolism and appetite. Morselli, 2010
32 Short sleep duration and weight gain: a systematic review Patel, 2008
33 Short-Term Moderate Sleep Restriction Decreases Insulin Sensitivity in Young Healthy Adults. Wang, 2016
34 Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index Taheri, 2004
35 Sleep curtailment is accompanied by increased intake of calories from snacks Nedeltchva, 2009
36 Sleep Deprivation And Obesity In Adults: A Narrative Review Cooper, 2018
37 Sleep Deprivation Selectively Upregulates an Amygdala-Hypothalamic Circuit Involved in Food Reward. Rihm, 2019
38 Sleep disturbances, body fat distribution, food intake and/or energy expenditure: pathophysiological aspects. St-Onge, 2014
39 Sleep duration and weight loss among overweight/obese women enrolled in a behavioral weight loss program. O'Brien, 2012
40 Sleep duration, sleep quality and body weight: parallel developments. Gonnissen, 2013
41 Sleep Extension Increases the Effect of Caloric Restriction Over Body Weight and Improves the Chronic Low-Grade Inflammation in Adolescents With Obesity. Moreno-Frias, 2020
42 Sleep extension is a feasible lifestyle intervention in free-living adults who are habitually short sleepers: a potential strategy for decreasing intake of free sugars? A randomized controlled pilot study Khatib, 2018
43 Sleeping habits predict the magnitude of fat loss in adults exposed to moderate caloric restriction. Chaput, 2012
44 Sleeping hours: what is the ideal number and how does age impact this? Chaput, 2018
45 The fall in leptin concentration is a major determinant of the metabolic adaptation induced by caloric restriction independently of the changes in leptin circadian rhythms. Lecoultre, 2011
46 The metabolic consequences of sleep deprivation Knutson, 2007
47 The role of sleep duration in the regulation of energy balance: effects on energy intakes and expenditure. St-Onge, 2013


Additional References

Citation number Study title First author and year
48 Why we sleep: the temporal organization of recovery

Mignot, 2008

49 Physiology, Sleep Patterns


Jawabri, 2021

50 Sleeping hours: what is the ideal number and how does age impact this?

Chaput, 2018

51 Interrelationship between sleep and exercise: a systematic review Dolezal, 2017
52 Recommended amount of sleep for a healthy adult: a joint consensus statement of the american academy of sleep medicine and sleep research society Watson, 2015
53 National Sleep Foundation’s sleep time duration recommendations: methodology and results summary Hirshkowitz, 2016
54 A randomized controlled pilot trial of sleep health education on body composition changes following 10 weeks' resistance exercise Jåbekk, 2020
55 Sleep and muscle recovery: endocrinological and molecular basis for a new and promising hypothesis Dattilo, 2011
56 The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment Lamon, 2021
57 The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men Saner, 2020