Knowledge Center

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 examined the effects of insufficient sleep on weight gain and looked specifically at energy intake (calories in) and energy expenditure (calories out). Researchers investigated 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 14-15 day inpatient study. All volunteers were in good health, and at a healthy weight. Participants spent the roughly 2-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 3 days. During this time participants were allowed to sleep to a maximum of 9 hours per night. Their eating was regulated during this 3-day period so they were only consuming what they needed to maintain their initial weight.

Next, researchers split participants into 2 groups. One group continued to be allowed to sleep for as much as 9 hours nightly. The other group was limited to 5 hours of sleep per night. They slept this way for 5 consecutive nights, in a sleep pattern designed to mimic a typical workweek. During this 5-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 5 days, the groups switched sleep schedules, for another 5-day cycle. During both 5-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. Researchers found:

• Participants whose sleep was restricted to 5 hours a night for 5 consecutive nights burned 5% more overall calories daily than those who were allowed to sleep up to 9 hours per night. However, the daily calorie intake of restricted sleepers was 6% higher than longer sleepers. The result? An energy imbalance for restricted sleepers, with more calories consumed than used.
• This energy imbalance led to an average weight gain of almost 2 pounds for those in the restricted sleep phase.
• The 5-day restricted sleep pattern also resulted in alterations to participants’ circadian rhythms: the onset of nighttime melatonin release was delayed, and wake times occurred earlier.
• Eating patterns also changed among participants in the 5-hour nightly sleep phase. People ate less early in the day, and pushed more of their eating to evening hours. In particular, people whose sleep was restricted snacked more at night. Evening snacks increased to the point where the calories consumed in these late-day snacks exceeded the calories consumed in any single meal during the day.
• When people moved from restricted sleep to the longer sleep period, their daily calorie intake reduced. In particular, researchers saw a drop in fat and carbohydrate consumption. The transition resulted in slight weight loss among this group.
• Researchers found that men and women responded differently to sleep restriction, with regard to weight. Overall, women were able to maintain their weight during the 9-hour nightly sleep phase, during which they had unrestricted access to food. Men, on the other hand, were more likely to gain weight in this phase. But in the restricted-sleep phase, women were more likely to gain weight than men.

These results strongly align with other recent research on the impact of poor sleep on weight. In particular, we’ve seen other studies suggest the restricted sleep may make it more difficult for people to choose healthful foods, and that lack of sleep may contribute to a shift in calorie consumption to later in the day, to the detriment of our waistlines.

• A pair of recent studies indicates that sleep deprivation causes neurological changes that may compromise judgment and trigger desire for unhealthy foods. This study found that lack of sleep is associated with diminished activity in the brain’s frontal lobe, an area that’s critical to judgment and complex decision making. Participants who were sleep deprived made different, less healthy food decisions than those who were not. And in this study, researchers found that in people who were sleep deprived, the reward center of the brain was more strongly activated by unhealthy foods than in those who had received sufficient sleep.
• This 2011 study examined the timing of sleep and of eating, and their impact on weight. Researchers found that “night owls”—people with late bedtimes—did more of their daily eating in the evening, compared to those with earlier bedtimes. People with later bedtimes also slept less overall, and had lower quality sleep. Night owls consumed more calories at dinner and after 8 p.m. than those whose bedtimes were earlier.
• A study of mice found that alterations to a circadian-linked gene involved in hunger regulation caused the mice to become obese. Disruptions to this “clock gene” also altered the timing of the mice’s eating, causing them to consume more calories during the period normally reserved for rest.

The challenge of maintaining a healthy weight is a daily endeavor, made up of many small choices—What to eat? How much? When?—that over time have a powerful cumulative effect. A strong routine of sufficient nightly sleep can aid in this endeavor, helping your body and mind work at its best, every day, for weight control and overall health.

By Michael Breus, PhD, ABSM