Calories in, calories out. We’ve all heard this basic, fundamental calculation regarding weight loss and weight gain. To lose weight, we must expend more calories than we take in. Consume more than you need, and the result? The pounds go on. Turns out, lack of sleep may increase daily calorie consumption, and contribute to weight gain.

There is a tremendous amount of evidence that sleep plays an important role in weight management. Insufficient sleep is strongly linked to obesity and metabolic disorders, as well as to diabetes. But we’re still working to understand the underlying mechanisms by which sleep can influence weight.

A new study

A new study examined the effects of insufficient sleep on weight gain, and looked specifically at energy intake (calories in) and energy expenditure (calories out). Researchersinvestigated the effects of sleep on these two critical factors in weight management. What did they find? During periods of insufficient sleep, people increased their calorie consumption and, as a result, gained weight. What’s more, people who slept too little consumed more of their calories later in the day, which may further contribute to weight gain.

Researchers included 16 adults in a 14- to 15-day inpatient study. All volunteers were in good health, and at a healthy weight. Participants spent the roughly two-week study period in a controlled environment, where researchers could manage and monitor their sleep and eating patterns. Researchers collected baseline health and weight measurements from all 16 volunteers during the study’s first three days. During this time, participants were allowed to sleep to a maximum of nine hours per night. Their eating was regulated during this three-day period so they were only consuming what they needed to maintain their initial weight.

Next, researchers split participants into two groups. One group continued to be allowed to sleep for as much as nine hours nightly. The other group was limited to five hours of sleep per night. They slept this way for five consecutive nights, in a sleep pattern designed to mimic a typical workweek. During this five-day period, both groups were allowed the same unrestricted access to food. Participants were allowed to eat larger meals, and were given free access to snacks between meals. Snack foods included both low-calorie options like fresh fruit, and high-calorie, high-fat choices such as chips and ice cream. After five days, the groups switched sleep schedules for another five-day cycle. During both five-day phases, researchers conducted measurements and analysis of participants’ sleep and their energy expenditure.

Their results shed light on the relationship of sleep to calorie consumption and output, and on some of the ways that sleep may contribute to weight gain.

Read what the Researchers found

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