What do Americans have against sleep? The average amount of sleep has gone from 8 hours in the 1960s to 6.5 hours today, with as many as 30 percent of middle-aged Americans reporting less than 6 hours of sleep each night.[1] People don't realize that while our minds rest when we sleep, our bodies continue their never-ending work of trying to keep us balanced and healthy.

If you're conscious of your nutrition, the quality of your diet, and your body composition, you need to be just as conscious of your sleep. Along with regulating a myriad of other bodily functions, sleep has a direct impact on your appetite and hunger regulation, and on your body composition.

The Less Sleep You Get, the More Calories You Crave

To understand the impact of sleep on weight gain, you have to understand the distinction between hunger and appetite. Hunger arises from your body's need to obtain energy and nutrients—it's a physical thing. Appetite is a mental thing—it is the desire to eat, whether your body needs food or not. Lack of sleep throws the balance between hunger and appetite all out of whack.

To understand the impact of sleep on weight gain, you have to understand the distinction between hunger and appetite.

A 2004 sleep study limited 12 otherwise healthy, normal-weight men to 4.5-5 hours of sleep per night, while controlling their caloric intake and physical activity. Researchers found that lack of sleep decreased the amount of leptin, the hormone that signals satiety (fullness), by 18 percent. At the same time, lack of sleep increased by 28 percent the amount of ghrelin, a hormone which signals hunger.[2]

These changes in hormone levels really aren't fair. Just as the amount of the hormone that tells us we're hungry (ghrelin) goes up, the one that helps us control our appetite (leptin) goes down.[3]

Fatigue Impacts What You Eat and When You Eat It

The relationship between sleeping and needing more calories when you're awake makes sense: If you're sleeping less, you're awake more, and it takes more energy to be awake than to be asleep.[4] To compound the problem, changes in the levels of leptin and ghrelin brought about by inadequate sleep can cause people to consume significantly more calories than they need.[4]

Lack of sleep can also affect the kinds of food you eat and when you eat them. Fatigued people tend to eat more carb-heavy, sweet snacks the following day, and typically eat them in the late evening.[4,5]

Studies have shown that eating energy-dense foods late in the day can lead to weight gain.[6] This is the time of day when your metabolism starts to slow down because of lower levels of activity. With a slowed-down metabolism, your body doesn't need all of that caloric energy you've taken on with those energy-dense foods, so it stores it as fat.[7]

Bad News for Good Body Composition

In 2010, a team of researchers investigated the relationship between sleep and body fat. For two weeks, a study group of 10 overweight or obese men and women slept either 5.5 hours or 8.5 hours per night, while on a controlled 10 percent calorie-deficit diet.[8]

Since the diet was calorie controlled, all of the subjects lost about the same amount of weight. But the group that got only 5.5 hours of sleep lost more lean body mass and less fat mass than the control group. When you're working on your physique, that's the last thing you want to do.

During the first week, the men who slept less lost more weight than the others.

Another study looks at the effect less sleep had on 19 healthy men who typically got 7-7.5 hours of sleep per night. Some of the men were allowed to continue this pattern. Others had their sleep time decreased by 90 minutes for three weeks.[9] (All of the subject continued with their normal diets and slept at home.)

During the first week, the men who slept less lost more weight than the others. But for the next two weeks their weight continued to increase. This suggests that while many studies look at the effects of severe sleep restriction (like getting only 4-5.5 hours per night), more chronic but less severe lack of sleep can have a bigger effect on weight.

A third study concluded that a one-hour increase in sleep duration, combined with moderate caloric restriction resulted in a 1.5-pound decrease in fat mass.[10]

How Much Sleep Do You Really Need?

The overwhelming weight of evidence indicates that the average adult needs about 7-9 hours of sleep per night.[11] A majority of respondents to a sleep survey said they need about 7.5 hours of sleep per night to function well during the day.[12] What about you? Are you getting the sleep you need to crush your workouts?

If sleep is holding you back from reaching your health and body-composition goals, come up with a plan to up your game so that your time in bed works for, not against, your diet and health.


  1. Briançon-Marjollet, A., Weiszenstein, M., Henri, M., Thomas, A., Godin-Ribuot, D. and Polak, J. (2015). . Diabetology & Metabolic Syndrome, 7(1).
  2. Spiegel, K. (2004). . Annals of Internal Medicine, 141(11), p.846.
  3. Morselli, L., Leproult, R., Balbo, M. and Spiegel, K. (2010). . Best Practice & Research Clinical Endocrinology & Metabolism, 24(5), pp.687-702.
  4. Markwald, R., Melanson, E., Smith, M., Higgins, J., Perreault, L., Eckel, R. and Wright, K. (2013). . Proceedings of the National Academy of Sciences, 110(14), pp.5695-5700.
  5. Nedeltcheva, A., Kilkus, J., Imperial, J., Kasza, K., Schoeller, D. and Penev, P. (2008). American Journal of Clinical Nutrition, 89(1), pp.126-133.
  6. Baron, K., Reid, K., Horn, L. and Zee, P. (2013). Appetite, 60, pp.246-251.
  7. Oike, H., Oishi, K. and Kobori, M. (2014). . Current Nutrition Reports, 3(3), pp.204-212.
  8. Nedeltcheva, A., Kilkus, J., Imperial, J., Schoeller, D. and Penev, P. (2010). . Annals of Internal Medicine, 153(7), p.435.
  9. Robertson, M., Russell-Jones, D., Umpleby, A. and Dijk, D. (2013). . Metabolism, 62(2), pp.204-211.
  10. Chaput, J. and Tremblay, A. (2012). . Obesity Facts, 5(4), pp.561-566.
  11. Golem, D., Martin-Biggers, J., Koenings, M., Davis, K. and Byrd-Bredbenner, C. (2014). . Advances in Nutrition: An International Review Journal, 5(6), pp.742-759.
  12. National Sleep Foundation. (2013). 2013 International Bedroom Poll. Retrieved May 2, 2017, from

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Adam Flanagan

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