How Does Sleep Affect Weight Loss?

Can sleeping enough help with fat loss and diet control? Get-Fit Guy Ben Greenfield weighs in.

Ben Greenfield,
Episode #299

It’s no secret that not sleeping enough, considered to be less than seven hours of sleep per night, can cause weight gain, even if you’re on a weight loss diet.

For example, in research published in the Annals of Internal Medicine, dieters were put on different sleep schedules comprised of adequate sleep (7+ hours per night) and not quite enough sleep (less than 7 hours per night). With adequate sleep, half of the weight the dieters lost was from fat, not muscle, and furthermore, those on a sleep-deprived diet experienced 55% less fat loss. The sleep-deprived group also felt significantly hungrier, had less satisfaction after meals, and lacked enough energy to exercise.

There are a few biological mechanisms that explain why not sleeping enough can make you fat or disrupt your diet.

For example, within just four days of sleep deprivation, your body’s ability to properly respond to insulin signals begins to diminish (University of Chicago researchers found a 30% drop insulin sensitivity caused by lack of sleep). When you’re not responsive to insulin, fat cells are far less able to release fatty acids and lipids to produce energy, blood glucose remains higher, and any extra fats and sugars circulating in your blood cause you to pump out even more insulin. Eventually, all this excess insulin causes you to begin storing fat in all the wrong places, including tissues like your liver, leading to problems such as fatty liver and diabetes.

But insulin isn’t the only hormone affected by lack of sleep. Hunger is controlled by two other hormones that respond to sleep cues: leptin and ghrelin. Leptin is a hormone that is produced in your fat cells, and the less leptin you produce, the more your stomach feels empty and the less satiating a meal is. Ghrelin, on the other hand, stimulates hunger while also reducing metabolic rate and increasing fat storage. Research in the Journal of Clinical Endocrinoloy and Metabolism has shown that sleeping fewer than six hours reduces leptin and stimulates ghrelin: causing you to feel more hungry and less satiated!

Then there’s the hormone cortisol. When you don’t sleep enough, your cortisol levels rise. Not only does cortisol upregulate food reward centers in your brain that make you want to eat more food, but cortisol can also inhibit the breakdown of fat for energy and increase breakdown of muscle.


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