It’s during sleep that your body repairs. Unfortunately, most people don’t get enough deep, restful sleep for good health. What you might not realize is that skimping on sleep can have a negative effect on your body composition.


How Sleep Contributes to Weight Gain


One way that sleep affects body composition is by increasing appetite. A number of studies show that people who sleep less than 6 or 7 hours per night are more likely to be overweight or obese. It isn’t just that people who sleep less have more time to eat. Lack of sleep and irregular sleep habits triggers a rise in ghrelin, a powerful appetite hormone that gives you the munchies. It also suppresses leptin, a hormone that signals you’re full and no longer need to eat.


In fact, subjects who slept only 4 hours per night two nights in a row experienced an 18% decrease in leptin and a 28% rise in ghrelin. That combination can make you hungry! Unfortunately, the kind of hunger changes these hormones trigger is for sugary fare and processed carbohydrates, not the stuff you want to eat to stay slim and healthy. You can imagine how this would lead to weight gain and a rise in body fat over time.


It’s one thing for lack of sleep to affect appetite hormones, but do people gain weight when they sleep too little? In one study of 276 young and middle-aged adults, short sleepers gained, on average, 1.98 kilograms more than did average sleepers. Short sleepers are those who sleep between 5 and 6 hours per night, while average sleepers snooze 7 to 8 hours each night.


However, more sleep is detrimental to weight control too. Long sleepers, those who slept 9 to 10 hours nightly, gained 1.58 kilograms more than average sleepers over 6 years. So, neither extreme of sleep is beneficial for body weight and body composition. Based on this study and other research, 7 to 8 hours of sleep nightly is optimal. However, this study also shows that sleeping too little really can lead to weight gain. It’s not just theoretical.


Lack of Sleep Can Increase Muscle Loss Too


If you’re over the age of 30, you’re already slowly losing muscle mass because of aging, and the loss speeds up after the age of 50. If you skimp on sleep too much, it can trigger additional muscle loss. Why might this be? Chronic sleep loss can trigger a rise in the stress hormone cortisol, and an overabundance of cortisol causes muscle breakdown and muscle loss. Plus, your muscles repair during deep sleep. As your body drifts into the deepest stage of sleep called slow-wave sleep, your brain releases growth hormone that aids in muscle repair and the synthesis of new muscle tissue. So, not sleeping enough can make it harder to build muscle if you strength train, or to retain muscle if you don’t.


The Bottom Line


Not sleeping enough can trigger an increase in appetite, and that can lead to substantial weight gain over months to years. Based on current research, sleeping 7 to 8 hours per night is ideal for appetite and weight control. Not sleeping can contribute to muscle loss too, since lack of sleep and poor sleep reduces the amount of growth hormone your muscles can benefit from. Plus, growth hormone plays a role fat burning too, so it helps with fat loss.


In addition, too little sleep is a stressor on your body. The stress of not enough sleep increases cortisol, and that can lead to muscle loss. Research also suggests that not sleeping enough increases the risk of other health problems, including cardiovascular disease and type 2 diabetes. So, make getting enough sleep a priority, especially if you’re trying to lose weight.


Sleep quality counts too. If you’re tossing and turning, you’re not getting quality sleep and you could suffer from the same problems, like weight gain and muscle loss, that people who skimp on sleep do. Just as you keep a food and exercise diary when you’re trying to lose weight, keep a sleep journal too. Document how many hours you sleep each night and rate the quality of that sleep. It’s that important.



References: “Sleep loss boosts appetite, may encourage weight gain”

Sleep. 2008 Apr 1; 31(4): 517-523.doi: 10.1093/sleep/31.4.517.

Sleep . 2005 Oct;28(10):1289-96. doi: 10.1093/sleep/28.10.1289.

Sleep. 2004;27:661-666. “Just One Night of Poor Sleep May Add to Weight Gain, Muscle Loss”

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