Written by: Reneé Prince
Updated March 10, 2021
The rise in obesity rates (1) over the last few decades closely parallels the shorter and shorter sleep times reported by the American population. Although more research is needed to understand exactly how sleep affects weight, many researchers agree that poor sleep may be a risk factor for obesity (2).
Approximately one-third of Americans regularly sleep less than the recommended seven hours, and research suggests that sleeping less than six hours a night can raise the risk of obesity by at least 27% (3). Maintaining a consistent sleep schedule appears to lower the risk of being overweight (4), while short sleep, fragmented sleep, and even too much sleep are all considered risk factors for being overweight.
How Does Sleep Affect Weight Loss?
Sleep loss causes a number of changes to the brain and body that might make it more difficult to lose weight. These include changes to metabolism and hormones, as well as changes to our meal timings, exercise levels, and appetite.
Sleep Deprivation Alters Metabolism
Sleep plays a key role in regulating our metabolism, the process by which the body converts the food we eat into the energy that we need to function. Because our metabolism slows during sleep, spending more time awake means that we consume slightly more energy (5). The body compensates for this energy loss by lowering metabolism rates the next morning, meaning we don't burn as many calories.
Sleep Loss Affects the Brain's Reward System
To further compensate for the energy lost by staying awake instead of sleeping, the brain also ramps up activity in its reward centers (6), inducing cravings for highly caloric food (7). Certain brain regions that control how we judge foods (8) based on their odor and flavor are known to suffer disruptions after sleep deprivation.
A recent study proposed that sleep loss may increase levels of an endocannabinoid (9) that drives reward-seeking behavior in the form of tasty food. When food is readily available, we end up consuming more calories than would be required (10) to make up for the small amount of energy lost by staying awake.
A Lack of Sleep Influences Appetite and Food Choices
Sleep deprivation has been shown to lower levels of leptin, the hormone that promotes feelings of satiety and raises levels of ghrelin, the hormone that stimulates our appetite. These altered hormone levels make it easy to overeat when we are tired.
Studies have shown that sleep-deprived individuals or those with inconsistent sleep times are more likely to choose larger portion sizes and favor sweet, salty, starchy, and fatty (11) foods. Unfortunately, these food choices may cause a snowball effect, as a diet high in sugar and saturated fats (12) can lead to poorer-quality sleep.
Sleep Loss Pushes Back Meal Timings
Being awake until late at night leaves more time for eating. There is some evidence to show that night owls consume more of their calories later in the day, often skipping breakfast and snacking on carbohydrate-rich foods (13) after dinner. Unfortunately, late-night snacking (14) can make it more difficult to fall asleep, and it can lead to lighter sleep when you do drift off.
Eating during the biological night, or the time when a person usually becomes tired and goes to sleep, has also been linked to decreased glucose tolerance and weight gain (15). This connection is supported by studies of shift workers with irregular eating schedules, who are at a higher risk for diabetes (16).
Sleep Deprivation Favors Fat Cells and High Blood Sugar
If you're following a diligent diet but you're still not happy with your body make-up, the answer may lie in the way our muscle and fat tissues respond to sleep loss. It turns out that long-term sleep deprivation induces changes in metabolism (17) that encourage the body to burn muscle instead of fat (18).
Sleep deprivation in humans also raises levels of cortisol (19), the stress hormone, as well as certain proteins that are involved with inflammation (20). These changes contribute to insulin resistance and higher blood sugar levels, raising the risk of type 2 diabetes, high blood pressure, and heart disease.
Sleep Loss May Reduce Physical Activity
Researchers suspect that one reason for the link between sleep deprivation and weight gain is the simple fact that sleep-deprived people are more sedentary. This theory is supported by studies of children that found that those with irregular sleep schedules spent less time exercising. Along the same lines, sleep-deprived individuals with busy schedules may have less time to prepare meals, making them more likely to reach for prepared foods that are high in calories.
Sleep and Weight Loss: A Bidirectional Relationship
There is a wealth of evidence to suggest a relationship between sleep and weight gain, but it's difficult to say whether one influences the other, or both are influenced by a third factor. The encouraging news is that regularly getting an appropriate amount of sleep has been shown to help with weight loss (21) and better health overall. If you're having trouble managing weight, ask your doctor for advice on sleep hygiene to complement a healthy diet and regular exercise plan.
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