Not getting enough sleep doesn’t just mean waking up tired. Over time, it can change the way your body manages weight, reduce your daily physical activity, and worsen certain indicators related to metabolic health.
This is shown in a study from Columbia University, published by researchers at the Vagelos College of Physicians and Surgeons, which found that a reduction of about 80 minutes of sleep per night over six weeks was associated with an average weight gain of about half a kilo and an increase in the amount of time spent on sedentary activities.
This may seem like a small increase, but it becomes significant when you consider that it covers just a month and a half. According to the authors, maintaining such a reduction in sleep over time could contribute to clinically significant weight gain.
Sleeping 5 hours instead of 7
Until now, many studies on the relationship between sleep and obesity had focused on extreme situations: people forced to sleep about four hours a night for a few days. This is a useful model for understanding the effects of acute sleep deprivation, but it is far removed from real life. The Columbia University study sought to answer the question: What happens to people who consistently sleep a little less than they need to?
It is a very common condition: about 30% of adults routinely sleep 5–6 hours a night, often without noticing any immediate consequences.
Six weeks of less sleep, half a kilo heavier
The study involved 95 adults who normally slept 7–8 hours per night. For six weeks, they were asked to go to bed about 90 minutes later than usual. A wrist-worn device then tracked their actual sleep and physical activity levels. The actual reduction in sleep was about 80 minutes. After this period, the participants gained an average of about half a kilo.
The finding does not mean that everyone who gets little sleep will automatically gain weight, but it suggests that chronic sleep deprivation can put the body in a state that is less conducive to maintaining a healthy weight.
More hours awake, but less physical activity
One of the most interesting findings concerns physical activity. With less sleep, the participants did not use the extra time they were awake to be more active. On the contrary, they remained seated for longer periods: on average, 17 more minutes per day, with increases of nearly 30 minutes among men and postmenopausal women. This is an important detail, because a sedentary lifestyle is an independent risk factor for many chronic diseases.
Metabolism Pays the Price
The effects of sleep deprivation aren’t limited to weight gain. In an analysis conducted on a subset of the same participants, women with an already elevated cardiometabolic risk showed an increase in insulin resistance after six weeks of sleep deprivation. This phenomenon was most pronounced in postmenopausal women. Another related study found, in people with high cardiovascular risk, an increase in immune cells involved in inflammatory processes in the heart.
According to Marie-Pierre St-Onge, the study’s lead author, addressing weight gain by focusing solely on diet and physical activity risks being an incomplete approach if sleep is neglected. The research does not suggest that sleeping more is a miracle cure for being overweight, but it highlights an increasingly evident fact: sleep is not just a period of inactivity. This is a phase in which the body regulates fundamental processes, from metabolism to energy balance.
