Better sleep means a fitter body

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“Sleep is the interest that we pay on capital that is recovered upon death, and the more we pay this interest regularly, the more the date of capital recovery will be postponed.” That saying by the philosopher Schopenhauer sums up the importance of sleep, which is no longer a period of rest for the brain and body, but recent studies link its disruption to weight gain. The two most recent experimental studies I reviewed on the effect of lack of sleep on weight were published in July and October 2026. The first monitors a connection with the biological clock, and the second tests Actual reduction in sleep, July study: A loss of about 80 minutes of sleep increases weight within six weeks. It was published in the journal Annals of Internal Medicine under the title: “Short, extended sleep and its effect on body weight and composition: a pooled analysis of randomized trials,” led by researchers from Columbia University, and combined two trials that included 95 adults with factors that increase the risk of heart and metabolic diseases. Participants went through two periods, each six weeks long: a period of sufficient sleep, and another in which sleep was reduced, when sleep actually decreased by an average of 78 minutes each night, the following differences emerged compared to the period of adequate sleep:

Average weight gain of 450 grams.

Increase waist circumference by about half a centimeter.

Increase the time a person spends sitting or inactive by about 17 minutes per day.

The importance of the study is that it tested a moderate deficiency similar to that of many people staying up late, and showed that this deficiency may contribute to weight gain, but the increase was limited, and the follow-up was short. It is not correct to assume that it will repeat itself at the same rate every six weeks, or to consider all the weight gained as fat. As for the October 10, 2026 study, published in the International Journal of Obesity, it included 809 people, and measured exposure to light and wrist temperature during a week as indicators of the circadian rhythm, and found an association between poor regularity of these rhythms and worse metabolic indicators, and between some rhythm indicators and higher fat and body mass index in women.

But this study does not prove that rhythm disturbance is what caused obesity, and it did not test increasing sleep hours as a treatment. But what are the reasons for this conditional link between disturbed sleep and obesity?

First: increasing appetite and desire for high-calorie foods. Sleep deprivation affects the reward circuits in the brain, making sweets and fatty meals more tempting. It may change hunger and satiety hormones, such as ghrelin and leptin, but the pattern of these changes is not consistent in all studies.

Second: Staying up late prolongs the time available for eating, especially snacks at night. Experiments have shown that the calories of these meals increase when sleeping hours are reduced.

Third: Lack of sleep may reduce the body’s sensitivity to insulin, weakening its ability to regulate blood sugar. Also, the disruption of the biological clock affects the way food is processed, so your fitness starts from a bed without snoring, a quiet continuous sleep of 6-8 hours, without an annoying mobile phone next to you.