Sleep and Obesityby Viatcheslav Wlassoff, PhD | November 23, 2014
Thanks to the obesity epidemic, we’ve seen an explosion of research on the problem of excess weight and the physiological mechanisms of weight control. It has turned out that body weight balance is far from the simple arithmetic of “calories in” and “calories out”. What has surprised many researchers, however, is the clear connection between gain in body weight and lack of sleep.
As with many other aspects of obesity, the connection between excess weight and inadequate sleep was clearly documented only recently. The most convincing evidence of this connection came from the study of nurses in the U.S. This study monitored various health and lifestyle parameters of approximately 7,000 health workers over a period of 16 years. It turned out that female nurses who regularly slept five hours or less per day were 32% more likely to put on additional 15kg or more over the study period. The effect of the lack of sleep on the weight gain was further confirmed by meta-analysis of multiple studies which altogether covered more than 600,000 people.
These studies, obviously, don’t give a clue about the physiological mechanisms behind the observed weight gain. Further research, however, revealed two interesting phenomena. Firstly, it turned out that the lack of sleep at night leads to the imbalance of appetite-controlling hormones during the day. Sleep deprivation results in a substantial decrease of the level of leptin and serious increase of ghrelin. This, in turn, results in much stronger appetite and hunger, particularly in food cravings towards carbohydrate-laden foods.
The latter aspect of sleep deprivation attracted further interest of neuroscientists. They found that lack of sleep results in a rise in amygdala activity and deactivation of the anterior cingulate. These two brain structures are involved in decision making and the control of behavior. The imbalance in their activity essentially means that after a bad night, our judgment center is simply not functioning well enough, thus leading us to poor choices when it comes to the quality and quantity of food. The studies show that this lack of judgment can easily increase the calorie intake by up to 300 calories per day, mostly in the form of “bad” calories such as sugary foods and drinks.
In addition, lack of sleep affects our basal metabolic rate. Basal metabolism is responsible for the burning of around 60% of all calories that we consume. Even relatively small changes in the basal metabolic rate may have a significant effect on the final balance of calories. Metabolic rate is also controlled by the brain. Basic metabolic rate decreases following the sleep deprivation by around 200 calories.
Taken together, changed brain activity and decreased metabolic rate may add up to 500 calories of excess calories per day. This is enough to add 6kg of weight per year with two days of bad sleep each week.
These days, we sleep 25% less time than 50 years ago. In 1960, an average American was sleeping eight and a half hours a night. By 2010, the sleep time of average adult reduced to six hours and twenty minutes. Problem of insomnia is very common, particularly among obese people. The problem, however, is often ignored as an inevitable consequence of modern lifestyle, even though many people are aware that chronic bad sleep is linked to serious problems such as increased risk of cardiovascular diseases.
Many researchers now believe that to properly address the problem of obesity, we also have to address the problem of inadequate sleep. Better sleep will not miraculously make you slim, but it will certainly prevent further weight gain. Over time, it will even help to shed some pounds. Anyone serious about weight loss should pay attention to their sleep pattern, in addition to their diet and level of physical activity.
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