Surprising Ways Too Little Sleep Can Affect Your Body Composition

Lack of sleep and body composition

Sleep is the ultimate reboot for your body and brain. At the end of a long day, it is exactly what your body longs for. No wonder! It’s during deep sleep that the information your brain processed during the day is consolidated into long-term storage. Sleep is also vital if you work out since your muscles recover and repair during sleep, mostly during the deep stages of sleep. Therefore, sleep matters for a healthy brain and for mental health.

Lack of sleep can also affect your body composition, and not in a positive way. Studies show that people who skimp on sleep are more likely to gain body fat. One reason is the lack of sleep affects appetite hormones like leptin and ghrelin that control appetite. Skimping on sleep decreases leptin and boosts ghrelin and that leads to an increase in appetite. Plus, the food choices you make won’t be as healthy in a sleep-starved state. When you’re tired, you’re more likely to reach for whatever is convenient or you may crave ultra-processed carbs and sugar foods. These cravings may be your body’s way of asking for energy.

What you may not realize is lack of sleep or poor sleep can affect muscle tissue and the ability to make muscle gains too. If you strength train, you understandably want to hang on to the muscle you’ve worked so hard to build. If that’s the case, turn in to bed early and get your seven-plus hours. Here’s why.

What a Study Showed

To look at the impact of sleep on body composition, researchers asked fifteen healthy young men to stay up all night. In a separate session, they allowed them to sleep for 8.5 hours. After their respective sleep sessions, they took blood samples along with samples of fat and muscle tissue to see how the different sleep interventions affected muscle and fat metabolism.

Their findings? When the men skimped on sleep, they experienced a decline in metabolic activity in muscle tissue but a bump up in the activity of adipose tissue. If you’re trying to get a healthier body composition, more muscle, and less fat, that’s exactly what you don’t want.

What is the underlying mechanism for the decline in muscle metabolic activity and the rise in fat cells activity? One other finding was the men who didn’t sleep experienced a surge in the stress hormone cortisol, a hormone that breaks down muscle tissue. The rise in cortisol could explain this finding.

But there’s more to the story. The researchers also found the subjects who lost sleep experienced changes in gene expression that favor fat storage and increase muscle breakdown. So, skimping on sleep offers a double hit to your body physique-greater fat storage and more muscle breakdown.

Be Consistent with Your Sleep Schedule Too

It’s not just the amount of sleep you get, it’s also important to be consistent with your sleep habits. A study published in the American Journal of Health Promotion showed that turning in and awakening at the same time daily is better for your health and your body composition and weight. In fact, the study found that people who had sleep and wake times that varied by more than 90 minutes throughout the week had higher body fat percentages. In this study, researchers concluded that 8 to 8.5 hours of sleep per night was optimal for weight and body fat control.

If possible, stick to a regular sleep schedule on the weekends too. Many people are consistent with their sleep times during the week and stay up late on the weekend since they aren’t on a schedule. This disrupts your body’s internal biological clock and can make it harder to get back on track. You’ll feel better and more rested if you have a designated sleep and wake time and stick to it.

Lack of Sleep Can Affect Your Health Too

Beyond body composition, not sleeping enough can impact your health and increase the risk of health problems. For example, research shows lack of sleep reduces insulin sensitivity and makes it harder for your body to process glucose. When insulin sensitivity goes down, it’s easier for your body to store fat rather than burn it. In fact, one researcher points out that one night without sleep could be as harmful to insulin sensitivity as six months of a bad diet. When you deprive your body of sleep, it triggers hormonal changes that worsen insulin sensitivity and increase appetite. Plus, you’re more likely to get the munchies since lack of sleep increases the appetite hormone ghrelin and the stress hormone cortisol.

The Bottom Line

We often prioritize exercise and diet but are less mindful of good sleep habits. It’s not just what you eat and how much you move your body, it’s also how much you sleep and the quality of that sleep.

Even if you eat a healthy diet and exercise, depriving your body of sleep can impact your body composition by:

  • Increasing fat storage
  • Reducing muscle metabolic activity and muscle building

If you’re trying to gain muscle and lose body fat, focus on your sleep habits too. Make sure you’re getting enough sleep and that your sleep times are consistent, even on the weekend. Sleeping enough is also important for your overall health. Make it a priority!



  • “The Impact of Sleep Deprivation on Hormones and Metabolism” January 30, 2017.
  • National Sleep Foundation. “How Much Do We Really Need?”
  • Tufts Health and Nutrition Letter. “Chronic sleep Loss May Impact Body Composition”
  • Science Daily. “Consistent Bed, Wake Time Linked to Healthier Weight”
  • Bruce W. Bailey, Matthew D. Allen, James D. LeCheminant, Larry A. Tucker, William K. Errico, William F. Christensen, Marshall D. Hill. Objectively Measured Sleep Patterns in Young Adult Women and the Relationship to Adiposity. American Journal of Health Promotion, 2013; 131107080257006 DOI: 10.4278/ajhp.121012-QUAN-500.
  • Endocrinol Metab Clin North Am. 2013 Sep; 42(3): 617–634. doi: 10.1016/j.ecl.2013.05.001.
  • com. “Insulin sensitivity: One night of poor sleep could equal six months on a high-fat diet, study in dogs suggests”


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