Sleep

Short sleep during a diet means losing more muscle and less fat

When people slept less while dieting, they lost about the same weight but a much larger share of it came from lean tissue. Sleep is part of a successful cut.

Most diet advice focuses on calories, protein and training, but sleep quietly decides what kind of weight you lose. In a well-known controlled study, adults followed the same calorie deficit for two weeks, once with 8.5 hours in bed and once with 5.5 hours. Total weight loss was similar, yet with short sleep the share coming from fat dropped by more than half and the share from fat-free mass, which includes muscle, rose sharply. Participants also reported more hunger when sleep was cut.

Several mechanisms likely contribute. Sleep loss shifts appetite hormones toward more hunger and craving for energy-dense food, raises stress hormones, lowers the body's sensitivity to insulin and can reduce testosterone in men. Training quality also suffers after poor nights, so the signal that tells the body to keep its muscle becomes weaker. Combined with a calorie deficit, this makes muscle more vulnerable at exactly the time you are trying to protect it.

During a cut, treat sleep as seriously as your meal plan. Aim for seven to nine hours with a consistent bedtime and wake time, keep caffeine to the morning and early afternoon, and avoid very large deficits that leave you too hungry to sleep. If your nights are short because of work or family, a moderate deficit, high protein and well-planned strength training become even more important. You will lose fat faster and keep more of the muscle you worked to build.

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