By Jessica Currier
Many observational and epidemiological studies have shown a connection between obesity and sleep deprivation in Americans. Alarmingly, 28% of American adults sleep less than six hours a night. One common reason for this connection is that sleep restriction affects the regulation of appetite hormones like ghrelin and leptin. Energy balance is tightly regulated by a hormonal system, involving ghrelin and leptin, which conveys information from the body to brain centers that control energy intake and expenditure (1). Restricted sleep is thought to increase ghrelin and decrease leptin, which promotes hunger (2). Sleep restriction is also thought to increase cortisol release, increasing eating behavior (2). Another proposed mechanism is that people, who stay awake longer, are exposed to a higher energy intake, specifically by snacking (2). Nevertheless, these explanations have been questioned. The effect of neuronal activity to food stimuli, an increase in energy intake, and the effect on energy expenditure will be reviewed in relation to sleep deprivation and obesity.
In one study published in The American Journal of Clinical Nutrition, researchers examined the effect on brain response to food stimuli in habitual and restricted sleep normal weight individuals (1). The neuronal pattern found in the restricted sleep group was similar to one that would occur when the body is at a low body weight and is trying to restore body stores (1). This study concluded that the restricted sleep group had a greater food intake and greater brain stimuli to areas that are linked with motivation and desire (1). The stimulated brain areas were the orbitofrontal cortex, insula, thalamus, precuneus, cingulate, gyrus, and supramarginal gyrus. (1). With food being widely accessible, this could be one reason associated with weight gain during sleep restriction. However, studies have shown that there are differences between brain responses to satiety and food stimulation in obese and lean individuals (1). Further research needs to be conducted to see if sleep restriction affects this difference.
Sleep deprivation has been shown to increase energy intake. In another study published in AJCN, researchers found that normal weight women had a significantly higher food intake, specifically in saturated fat, compared to men when sleep was restricted (2). The study did not find an increase in overall energy expenditure. It needs to be noted that gonadotropic-influenced hormones, like estrogen, could have an effect on energy intake (3). High levels of circulating estrogen across the menstrual cycle have been shown to influence energy intake, making food intake lowest during ovulation (3).
Lastly, sleep deprivation is believed to affect overall energy expenditure. Energy expenditure was examined in a group of healthy adolescent boys when sleep was restricted. The results included an increased energy expenditure from increased wake time in the sleep-restricted group while the control group was sleeping (4). There was no change in basal metabolic rate between the conditions (4). No differences in ghrelin and leptin levels were found between the control group and restricted sleep group. Interestingly, this study also found that the adolescents with restricted sleep had a decreased motivation to eat, the opposite of many other experiments.
The link between obesity and sleep deprivation could be a crucial understanding right now due to the alarming rates of obesity in our country. Many assumptions involving ghrelin, leptin, and cortisol have been formed but no known cause-relation effect has been determined. One feasible explanation of why sleep deprivation increases obesity or weight gain is because of brain stimulation and the fact that individuals are awake longer and will be exposed to food stimuli. With advertisements on television and kitchens stocked with food, it is hard to avoid exposure to food at night. If an individual is tired all the time, they are less likely to be physically active too. To decrease calorie intake and maintain a healthy weight strive for seven to nine hours of sleep each night!
1. St-Onge M, McReynolds A, Trivedi Z, Roberts A, Sy M, Hirsch J. Sleep restriction leads to increased activation of brain regions sensitive to food stimuli. Am J Clin Nutr. 2012;95:818-24.
2. St-Onge M, Roberts A, Chen J, Kelleman M, O’Keeffe, RoyChoudhury A, Jones P. Short sleep duration increases energy intakes but does not change energy expenditure in normal-weight individuals. Am J Clin Nutr. 2011;94:410-6.
3. Benedict C. Letters To The Editor: Compromised sleep increases food intake in humans: two sexes, same response. Am J Clin Nutr. 2012;95:531.
4. Klingenberg L, Chaput J, Holmback U, Jennum P, Astrup A, Sjodin A. Sleep restriction is not associated with a positive energy balance in adolescent boys. Am J Clin Nutr. 2012;96:240-8.