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London, UK Posted 2 years, 6 months ago

Does Sleep Affect Weight Loss?

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.

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 [2423]. 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 [29555657].

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 [2931].

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 (544341).

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


Read the full article at: sci-fit.net

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