It's no secret that not sleeping enough - which is typically considered to be less than seven hours of sleep per night - can cause weight gain, even if you're on a weight oss diet.
For example, in research published in the Annals of Internal Medicine, dieters were put on different sleep schedules comprised of adequate sleep (7+ hours per night) and not quite enough sleep (less than 7 hours per night). With adequate sleep, half of the weight the dieters lost was from fat, not muscle, and furthermore, those on a sleep-deprived diet experienced 55% less fat loss! The sleep-deprived group also felt significantly hungrier, had less satisfaction after meals, and lacked enough energy to exercise.
There are a few biological mechanisms that explain why not sleeping enough can make you fat or disrupt your diet.
For example, within just four days of sleep deprivation, your body's ability to properly respond to insulin signals begins to diminish (University of Chicago researchers found a 30% drop insulin sensitivity caused by lack of sleep). When you're not responsive to insulin, fat cells are far less able to release fatty acids and lipids to produce energy, blood glucose remains higher, and any extra fats and sugars circulating in your blood cause you to pump out even more insulin. Eventually, all this excess insulin causes you to begin storing fat in all the wrong places, including tissues like your liver, leading to issues such as fatty liver and diabetes.
But insulin isn't the only hormone affected by lack of sleep. Hunger is controlled by two other hormones that respond to sleep cues: leptin and ghrelin. Leptin is a hormone that is produced in your fat cells, and the less leptin you produce, the more your stomach feels empty and the less satiating a meal is. Ghrelin, on the other hand, stimulates hunger while also reducing metabolic rate and increasing fat storage. Research in the Journal of Clinical Endocrinoloy and Metabolism has shown that sleeping fewer than six hours reduces leptin and stimulates ghrelin: causing you to feel more hungry and less satiated!
Then there's the hormone cortisol. When you don't sleep enough, your cortisol levels rise. Not only does cortisol upregulate food reward centers in your brain that make you want to eat more food, but cortisol can also inhibit the breakdown of fat for energy and increase breakdown of muscle.
As if all these hormonal issues from lack of sleep weren't enough of an issue, it's also been shown in research that lack of sleep also causes your brain to be less resistant to the temptation of junk foods, excess calorie intake and foods you know you shouldn't eat. One study published in Nature Communications found that a single night of sleep deprivation is enough to impair activity in a section of your frontal lobe that controls food-related decision-making, which is one reason why it's so much easier to mow through an entire bar of chocolate, box of French fries or carton of ice cream when you're sleep deprived. When sleep deprived, you also have increased activity in the amygdala, a reward region of your brain that can make you crave high-calorie or very fatty and salty foods. When you get enough sleep, you can often fight off these desire, but another area of your brain - a section called your "insular cortex" gets desensitized due to sleep deprivation, and this means you have more trouble fighting the urges to eat highly rewarding foods. In a nutshell, when sleep deprived, you simply don't have the mental clarity to make complex decisions with regards to the foods you eat or the foods you want to avoid.
If you think that you can simply go hit the gym to fight off all these weight gain issues that can arise from lack of sleep, you may want to think again. Brazilian research has shown that sleep debt decreases protein synthesis, causes muscle wasting, and can lead to a higher incidence of injuries - and also slows production of growth hormone, which can make it more difficult for your body to build muscle, to recover from exercise and to utilize fatty acids as a fuel.
Finally, research in Psychoneuroendocrinology has shown that sleep deprivation makes you select greater portion sizes of all foods, further increasing the likelihood of weight gain. So not getting enough sleep basically means you're constantly hungry, you want bigger portions, you want food that tends to be associated with weight gain, the deleterious hormonal and weight gain effect of these foods is significantly magnified, and you have trouble putting on the metabolism-boosting muscle that could potentially help you fight off all these issues.
So what can you do about it? In next week's episode, you're going to get plenty of tips to get adequate sleep, and you're also going to discover why oversleeping can be just as deleterious as undersleeping when it comes to weight gain!
In the meantime, check out my article on "How Sleep Cycles Work" for even more advanced information on sleep and sleep cycles.