Find out why a lack of sleep may negatively affect weight loss by increasing the likelihood of weight gain through increased caloric consumption.
New research is bolstering how important sleep is for a healthy weight. When you’re awake between 10 p.m. and 4 a.m., you’re more likely to take in extra calories, says a study from the University of Pennsylvania. People ate an average of 553 more calories when they were kept awake until the early morning. But a lack of sleep affects more than just late-night eating.
You Gain Weight
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.
While these studies were all observational, weight gain has also been seen in experimental sleep deprivation studies.
One study allowed 16 adults just five hours of sleep per night for five nights. They gained an average of 1.8 pounds (0.82 kg) over the short course of this study.
Additionally, many sleep disorders, like sleep apnea, are worsened by weight gain.
It’s a vicious cycle that can be hard to escape. Poor sleep can cause weight gain, which can cause sleep quality to decrease even further.
Poor sleep isn’t the only factor in weight gain, of course—there are several, including your genetics, your diet and exercise habits, your stress, and your health conditions. But the evidence is overwhelming: when sleep goes down, weight goes up.
And it doesn’t take a long time, or a lot of sleep deprivation, to bring the weight on. A fascinating study from researchers at the University of Colorado found that one week of sleeping about 5 hours a night led participants to gain an average of 2 pounds.
Lacking sleep, you experience multiple changes to your body that can lead to weight gain. Sleep deprivation causes changes in hormones that regulate hunger and appetite. The hormone leptin suppresses appetite and encourages the body to expend energy. Sleep deprivation reduces leptin. The hormone ghrelin, on the other hand, triggers feelings of hunger—and ghrelin goes up when you’re short on sleep.
Sleep deprivation changes what foods you’re most interested in eating, creating more intense cravings for fat and sugar-laden foods. Low on sleep, your brain can’t make reasoned decisions and use its best judgment about food, and you’re more likely to be impulsive and give into junk-food desires. (More on the powerful effects of sleep deprivation on the brain soon.)
We also know that even after a moderate amount of sleep deprivation, you’re likely to eat more the next day. And lack of sleep makes you more likely to eat more of your overall calories at night, which can lead to weight gain.
I talked a few weeks ago about a really interesting new study on sleep and sugar consumption, which showed that increasing sleep amounts reduced sugar intake significantly—by about 10 grams. The American Heart Association’s recommended maximum daily intake of added sugar is 36 grams for men, and 25 grams for women, which gives you some idea of just how significant a 10-gram reduction is. That study also showed boosting sleep amounts started participants on a trend toward lowering their fat and carbohydrate intake.
Poor Sleep Can Increase Your Appetite
Many studies have found that people who are sleep-deprived report having an increased appetite.
This is likely caused by the impact of sleep on two important hunger hormones, ghrelin and leptin.
Ghrelin is a hormone released in the stomach that signals hunger in the brain. Levels are high before you eat, which is when the stomach is empty, and low after you eat.
Leptin is a hormone released from fat cells. It suppresses hunger and signals fullness in the brain.
When you do not get adequate sleep, the body makes more ghrelin and less leptin, leaving you hungry and increasing your appetite.
A study of over 1,000 people found that those who slept for short durations had 14.9% higher ghrelin levels and 15.5% lower leptin levels than those who got adequate sleep.
The short sleepers also had higher BMIs. In addition, the hormone cortisol is higher when you do not get adequate sleep. Cortisol is a stress hormone that may also increase appetite.
Poor Sleep Can Increase Your Calorie Intake
People who get poor sleep tend to consume more calories. A study of 12 men found that when participants were allowed only four hours of sleep, they ate an average of 559 more calories the following day, compared to when they were allowed eight hours.
This increase in calories may be due to increased appetite and poor food choices, as mentioned above.
However, it may also simply be from an increase in the time spent awake and available to eat. This is especially true when the time awake is spent being inactive, like watching television.
Furthermore, some studies on sleep deprivation have found that a large portion of the excess calories was consumed as snacks after dinner.
Poor sleep can also increase your calorie intake by affecting your ability to control your portion sizes.
This was demonstrated in a study on 16 men. Participants were either allowed to sleep for eight hours or kept awake all night. In the morning, they completed a computer-based task where they had to select portion sizes of different foods.
The ones who stayed awake all night selected bigger portion sizes, reported they had increased hunger and had higher levels of the hunger hormone ghrelin.
Poor Sleep May Decrease Your Resting Metabolism
Your resting metabolic rate (RMR) is the number of calories your body burns when you’re completely at rest. It’s affected by age, weight, height, sex and muscle mass.
Research indicates that sleep deprivation may lower your RMR.
In one study, 15 men were kept awake for 24 hours. Afterwards, their RMR was 5% lower than after a normal night’s rest, and their metabolic rate after eating was 20% lower.
On the contrary, some studies have found no changes in metabolism with sleep loss. Therefore, more research is needed to determine if and how sleep loss slows metabolism.
It also seems that poor sleep can cause muscle loss. Muscle burns more calories at rest than fat does, so when a muscle is lost, resting metabolic rates decrease.
One study put ten 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.
A 22-pound (10-kg) loss of muscle mass could lower your RMR by an estimated 100 calories per day.
You Have Less Sex
You might have seen the recent news that nearly a third of American couples are interested in a “sleep divorce,” according to a new survey. More than 30 per cent of survey-takers said they’d prefer to sleep separately from their partners—and 10 per cent said they’d had an earlier relationship end oversleep issues. I understand and support the drive to get a good night’s sleep, even if that means partners were sleeping in separate beds. Rather than a “sleep divorce,” I’d prefer to see couples address the fundamental sleep issues that are driving them apart—whether that’s snoring, restlessness, sleeping in a bed that’s too small, or struggling to manage differing sleep schedules.
Attending to the core problems that are leading couples to consider sleeping apart would result in better sleep—and more sex.
We all know being tired can decrease the likelihood partners will want to have sex—especially at the end of a long day. (Despite the long-held social convention, 10 or 11 p.m. is, biologically-speaking, about the worst time to have sex, thanks in large part to low levels of the hormones that drive sexual desire. When are those arousal hormones at their highest? First thing in the morning.)
But the effects of sleep deprivation on sex lives go way beyond we’re-too-tired-tonight issue.
Sleep deprivation can affect both sexual arousal and sexual function, in both men and women, resulting in less pleasurable, less frequent sex. In men, sleep deprivation lowers testosterone. A recent study found one week of sleeping just under 5 hours a night sent testosterone levels in healthy young men plummeting 10-15 per cent. (There’s also worrisome research accumulating that sleeping too little—or too much—may reduce men’s fertility.) Sleep deprivation is also strongly linked to erectile dysfunction.
In women, sleep deprivation may also lower levels of testosterone, a hormone important to female sex drive. Research show sleep deprivation reduces physical arousal and desire in women—and that getting additional sleep boosts next-day arousal. The effects of poor sleep in women haven’t received the degree of scientific attention they deserve—we need more research to understand how sleep deprivation—especially a chronic sleep debt—might contribute to sexual problems in women.
Reading one another’s sexual interest also becomes harder when sleep deprived. A 2013 study found that men, when sleep-deprived even for a single night, overestimated women’s interest in sex. Scientists attributed this to the effects of sleeplessness on the brain’s frontal lobe, where we assess risk, manage inhibition, and make complex judgment calls.
You Look, and Feel, Older
During sleep—particularly during deep, slow-wave sleep, the body produces more human growth hormone, or HGH, and goes to work repairing and refreshing cells throughout the body—including cells of the skin, muscles, and bone. Short on sleep, you risk losing out on this important rejuvenation—and it’s going to show in how you look and feel.
Ever look in the mirror after a few nights of poor sleep and think your skin looks tired? Sleep is critical to the health of your skin—and its youthful appearance. The boost in HGH is related to increases in the production of collagen, the protein that gives skin its elasticity and firmness and helps keep wrinkles at bay. Research shows that sleep deprivation interferes with collagen production and can weaken the integrity of the skin.
Healthy, plentiful sleep is important to maintaining muscle mass—and sleep deprivation is linked to both reduced muscle mass and muscle strength in both men and women, particularly with age. Sleep deprivation also can interfere with bone health, reducing bone density and the production of new, strong bone.
Losing strength and mass in muscles and bones can affect everything from your posture to your flexibility to your ability to exercise and be active, to how well you heal after an injury. To stay looking and feeling youthful, we need our muscles and bones strong and ready to work for us—and they need sleep to do that work.
Your Risk for Accident and Injury Goes Through the Roof
Whether you’re at home, on the job, on the sports field or behind the wheel, when sleep-deprived, you’re at much higher risk for accident and injury. I’ve written before about the dangers that not getting enough sleep poses to your safety, and research that shows how insomnia is a major risk factor for accidental death.
The effects on the brain from sleep deprivation are in many ways similar to the effects of drinking too much alcohol—yet drowsy driving still doesn’t get nearly the attention as drunk driving. Some of the latest research from AAA shows drivers who slept even 1 hour less than they typically do are at significantly higher risk for motor-vehicle crashes. And the more sleep deprivation piles on, the higher the crash risk goes. The study found drivers who slept less than 4 hours the night before had more than 11 times the crash rate as drivers who slept seven or more hours a night.
The workplace becomes much less safe when you’re sleep-deprived. According to the National Sleep Foundation, highly sleep-deprived workers are 70 per cent more likely to be in work-related accidents than well-rested workers.
And a lack of sleep is linked to a higher risk of injury in athletes—including teenage athletes.
Accident risks are often talked about in relation to obstructive sleep apnea—and it’s true that the presence of OSA raises your risk of accident and injury significantly. But NOT having OSA doesn’t protect you against accidental injury, if you’re not getting enough sleep. No matter how your sleep is disrupted or cut short, you’re more vulnerable to accidents.
You Don’t Heal as Quickly from Illness and Injury
There’s brand new research that suggests sleep is more important than nutrition to healing. The study is particularly interesting because the scientists set out to test how a nutritional boost might speed wound healing, even in the presence of sleep deprivation. Instead, they found it was a sleep that accelerated healing—and a lack of sleep slowed it down. This is consistent with other research showing that sleep deprivation slows the healing process.
Sleep has a powerful effect on the immune system, so it’s not just wound healing, but all forms of recovery from illness, injury, and disease that are affected by sleep. Your risks for coming down with an illness are greater when you’re sleep-deprived, and it will take you longer to recover.
We’ve known for a while of the relationship between sleep and immune function. Both sleep and immune system activity are both regulated by circadian rhythms. And sleep—especially slow-wave sleep—is a time when the body’s immune activity goes into high gear, releasing more of its fighter cells, repairing damaged cells, and pushing back against the disease. From the common cold to cancer, we’ve seen scientific evidence supporting sleep’s role in fighting illness.
New research looked at the sleep patterns and immune function in pairs of identical twins, to show that sleep deprivation depresses the immune system. In a study that re-created real-world sleep patterns, scientists found the twins who slept less had less robust immune activity than their longer-sleeping siblings.
Along with eating right and exercising, getting quality sleep is an important part of weight maintenance. Poor sleep dramatically alters the way the body responds to food.
For starters, your appetite increases, and you are less likely to resist temptations and control portions. To make matters worse, it can become a vicious cycle. The less you sleep, the more weight you gain, and the more weight you gain, the harder it is to sleep.
If you’re sleep-deprived, you not only weaken your immune system, but also deprive yourself of the time when the body naturally does some of its best work to heal and repair itself.
Remember, when you’re sleep-deprived, you’re not just facing one of these issues: you’re more than likely grappling with all of them. Think about that the next time you’re tempted to shortchange your sleep because something else seems more important.