According to the Center For Disease Control, poor sleep has repeatedly been linked to a higher body mass index (BMI) and weight gain. People’s sleep requirements vary, but generally speaking, research has observed changes in weight when people get fewer than seven hours of sleep a night. A major review found that short sleep duration increased the likelihood of obesity by 89% in children and 55% in adults. Another study followed about 60,000 non-obese nurses for 16 years. At the end of the study, the nurses who slept five or fewer hours per night were 15% more likely to be obese than those who slept at least seven hours a night.
Those numbers are both frightening and comforting at the same time. If you’re trying to lose weight, you may be missing the most important factor – sleep. So many patients come to me frustrated at how hard they work at diet and exercise but still can’t lose weight. And there might be a good reason. Between eating healthier, watching your intake and exercising, they’re forgetting to sleep enough! More likely, they just didn’t realize that sleep is the key to seeing the benefit of all their hard work. According to the Centers for Disease Control and Prevention, more than 35% of people are sleep deprived, pretty much the same statistic for obesity. This is unlikely a coincidence. Studies are clearly showing sleep impacts weight.
Not sleeping enough- less than seven hours of sleep per night- can reduce and undo the benefits of dieting, according to research published in the Annals of Internal Medicine. In the study, dieters were put on different sleep schedules. When their bodies received adequate rest, half of the weight they lost was from fat. However, when they cut back on sleep, the amount of fat lost was cut in half- even though they were on the exact same diet. What’s more, they felt significantly hungrier, were less satisfied after meals, and lacked energy to exercise. Overall, those on a sleep-deprived diet experienced about half the reduction in fat loss compared to their well-rested counterparts.
According to a University of Chicago study, poor sleep affects fat cells. “Lack of sleep makes you fuzzy, exhausted, confused, grumpy. It’s not just your brain and body that feel that way- your fat cells do too. When your body is sleep deprived, it suffers from ‘metabolic grogginess'”. The term was coined by University of Chicago researchers who analyzed what happened after just four days of poor sleep- something that commonly happens during a busy week. They showed that one late night at work leads to two late nights at home, and next thing you know, you’re in sleep debt. It may not seem like a lot, but the hormones that control your fat cells don’t feel the same way. Within just four days of sleep deprivation, your body’s ability to properly use insulin becomes completely disrupted. In fact, the University of Chicago researchers found that insulin sensitivity dropped by more than 30%, causing insulin resistance. This is important because insulin is a hormone that moves sugar from the bloodstream into your body’s cells, to be used as energy. When cells become insulin resistant, more sugar remains in the bloodstream and the body produces more insulin to compensate. The excess insulin makes you hungrier and tells the body to store more calories as fat. Eventually this excess insulin ends up storing fat in all the wrong places, such as tissues, like your liver. This is exactly how you gain excess fat and develop diseases like diabetes.
According to research published in the Journal of Clinical Endocrinoloy and Metabolism- lack of rest makes you crave food. The belief that willpower can control hunger is not accurate. Hunger is controlled by two hormones: leptin and ghrelin. Leptin is a hormone that is produced in your fat cells. The less leptin you produce, the more your stomach feels empty. The more ghrelin you produce, the more you stimulate hunger while also reducing the amount of calories you burn (your metabolism) and increasing the amount fat you store. In other words, you need to control leptin and ghrelin to successfully lose weight, but sleep deprivation makes that nearly impossible. Research showed that sleeping less than six hours triggers the area of your brain that increases your need for food while also depressing leptin (which then prevents you from feeling satiated) and stimulating ghrelin (which increases hunger), a triple whammy.
Unfortunately there’s more; scientists at Harvard University discovered exactly how sleep loss makes it nearly impossible to lose weight. When you don’t sleep enough, your cortisol levels rise. This is the stress hormone that is frequently associated with fat gain. Cortisol also activates reward centers in your brain that make you want food. At the same time, the loss of sleep causes your body to produce more ghrelin. A combination of high ghrelin and cortisol shut down the areas of your brain that leave you feeling satisfied after a meal, so you feel hungry all the time no matter how much you eat.
It gets worse.
Skimping on sleep sets your brain up to make bad decisions. It dulls activity in the brain’s frontal lobe, the area of decision-making and impulse control. It’s a little like being drunk. You don’t have the mental clarity to make good decisions. Plus, when you’re overtired, your brain’s reward centers are more stimulated and satisfied by whatever feels good. So while you might be able to ignore unhealthy foods when you’re well-rested, your sleep-deprived brain may have trouble saying no to all that comfort food. A study in the American Journal of Clinical Nutrition found that when people were starved of sleep, even by one night, late-night snacking increased, and people were more likely to choose high-carb snacks. In another study done at the University of Chicago, sleep-deprived participants chose snacks with twice as much fat as those who slept at least 8 hours. In study after study, researchers found that a lack of sleep led to increased cravings for energy-dense, high-carbohydrate foods. A sleepy brain appears to crave junk food while also lacking the impulse control to say no. Add to this: research published in Psychoneuroendocrinology found sleep deprivation makes you select bigger portion sizes of all foods, increasing further the likelihood of weight gain. So not sleeping the recommended hours makes you constantly hungry, craving only comfort food high in calories, carbs and fat while finishing bigger portions all without the brain functioning well enough to say “STOP!”.
The impact of sleep deprivation spreads beyond diet and into workouts. Having some muscle on your body is important. Muscle is the enemy of fat, it helps you burn fat. But lack of sleep is the enemy of muscle. Scientists from Brazil found that sleep debt decreases protein synthesis (your body’s ability to make muscle), causes muscle loss, and can lead to a higher incidence of injuries. One study put 10 overweight adults on a 14-day diet of moderate calorie restriction. Participants were allowed either 8.5 or 5.5 hours to sleep. Both groups lost weight from both fat and muscle, but the ones who were given only 5.5 hours to sleep lost less weight from fat and more from muscle. Getting more sleep may also improve your athletic performance. In one study, college basketball players were asked to spend 10 hours in bed each night for five to seven weeks. They became faster, their reaction times improved, their accuracy increased and their fatigue levels decreased.
Just as important, the study showed that lack of sleep makes it harder for your body to recover from exercise by slowing down the production of growth hormone, your natural source of anti-aging and fat burning, that also facilitates recovery. This happens in two different ways: poor sleep means less slow-wave sleep, which is when the most growth hormone is released. A poor night of rest also increases the stress hormone cortisol, which also slows down the production of growth hormone. This means that the already reduced production of growth hormone due to lack of slow-wave sleep is further reduced by more cortisol in your system. It’s a vicious cycle. Sleep deprivation makes everything more challenging, including your workouts.
The connection between sleep and weight gain is hard to ignore. Research published in the American Journal of Epidemiology found that women who are sleep deprived are a third more likely to gain 33 pounds over the next 16 years than those who receive seven hours of sleep per night.
Losing weight isn’t just about feeling good and looking better, it’ll improve your overall health, decreasing the risks for diabetes, high blood pressure, cancer, heart disease, osteoarthritis, and cognitive issues (read more here). Clearly, getting at least 7-9 hours sleep should be an important part of everyone’s weight loss program. Not just once in awhile but every night. It might not seem like much, but one night tossing and turning can turn into 4 in a blink. Prioritizing sleep could make all the difference in losing those extra pounds.