For decades, we’ve been trained to think about weight as it relates to physical activity—as in, regular workouts are key to maintaining a healthy body weight. Yet as scientists’ understanding of obesity has evolved, it’s become clear that the relationship between exercise and weight isn’t quite so straightforward (nor is weight loss as simple as “calories in, calories out”). In fact, research shows that, as counterintuitive as it might sound, inactivity might be just as important as hitting the gym when it comes to achieving a healthy body weight and preventing obesity. More specifically, we’re talking about the importance of getting a good night’s sleep.
A growing body of evidence is exploring powerful links between sleep deprivation and the prevalence of obesity. In fact, many people increasingly view sleep deprivation and obesity as parallel epidemics, says clinical sleep educator Terry Cralle, RN, a Better Sleep Council representative. The relationship between sleep and weight is complex, but a few things are clear: “Sleep deprivation will lead to a decrease in metabolism, an increase in appetite, and a decrease in physical activity,” Cralle says.
Now, before you say, “Sleep deprivation—that’s not about me,” this term doesn’t just apply to people who routinely stay up until 2 a.m. watching TV and then wake at 6 a.m. for work (although that definitely counts). It can also just mean that you chronically fall short of the seven to nine hours of sleep recommended for adults. While going to bed an hour or two later might not feel like a huge deal the next day, falling just one or two hours short on sleep over the course of weeks or months has been shown to have a measurable impact on our waistlines.
Studies have shown that people who sleep less than seven hours a night (about one third of Americans, according to the Centers for Disease Control and Prevention) are more likely to have a higher body mass index (BMI) and are at higher risk of obesity than people who sleep the recommended number of hours. Other research has shown that people who sleep less than six hours a night are at increased risk for type 2 diabetes. Also important to note: Sleep deprivation isn’t just about the amount of sleep you get; it can also mean that the quality of your sleep is poor because, for example, you wake up frequently due to a partner’s snoring, or because of work stress, or because you’re a parent of little kids.
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Whatever the reasons that someone isn’t clocking enough Zs, there are several ways in which sleep deprivation makes weight management more challenging. For starters, “Chronic sleep deprivation can reduce the body's resting metabolic rate, meaning we burn fewer calories at baseline,” explains Dr. John Carter, director of the Center for Sleep Medicine at MetroHealth in Cleveland. Yet tired people typically have a higher caloric intake than people who sleep for a longer stretch. As you might have noticed, the day after a late night out, disrupted sleeping patterns often lead to nonstop snacking and cravings for high-calorie foods loaded with carbohydrates, which make us feel (temporarily) more upbeat. "When we're tired, we're more likely to reach for sugary foods and beverages to get a quick boost of energy,” says Dr. Christine Ren-Fielding, Professor of Surgery at NYU School of Medicine, Director of the NYU Langone Weight Management Program and Chief of the Division of Bariatric Surgery. Despite this increased food intake, our energy expenditure on tired days can be lower; when our energy balance is out of sync, this can lead to excess calories stored as fat.
Meanwhile, lack of sleep depletes our motivation, willpower, and decision-making abilities, meaning we’re more likely to cancel that Pilates class or skirt right past the produce section during our grocery run. Studies show that people with sleep loss eat fewer fruits and vegetables, which contain nutrients like fiber that are key to feeling full and maintaining steady energy levels throughout the day. “When you’re sleep deprived, you’re simply not in the mindset to make thoughtful, healthy choices. You’re too tired to plan, too drained to cook, and too overwhelmed to even think clearly,” says Chevy Mermelstein, a Montreal-based sleep coach. “That’s when we start reaching for the easy stuff—processed, packaged foods, sugary snacks, caffeine, or anything that gives a quick boost. Your body is desperate for energy and relief.”
Underlying all of this are the complex, hormonal reasons that sleep affects weight management. Insufficient sleep—due to short sleep duration, poor sleep quality, or both—alters the balance of the hormones that regulate things like appetite, metabolism, and fat storage. Without enough sleep, your body produces less leptin, known as the satiety hormone. Lower levels of leptin mean you’re less likely to feel full after you eat and more likely to keep reaching for more servings. On the flip side, lack of sleep is associated with an increase in ghrelin, the hunger hormone. Increased ghrelin levels have been shown to not only make people increase their overall food intake but also to specifically crave higher-calorie foods.
Another hormone that increases when you’re in a state of sleep deprivation is the so-called “stress hormone” called cortisol; higher cortisol levels are linked to increased abdominal fat, as well as muscle breakdown. They also affect insulin sensitivity, which decreases when you don’t get enough sleep. Put simply, lower insulin sensitivity means your body is less efficient at processing carbs, leading to elevated blood glucose and more storage of excess energy as body fat. (Not ideal at times when you’re grabbing chips straight from the bag to get through a sleepy afternoon slump.) And sorry, poor sleepers, but that’s not all. “Poor sleep also compromises slow-wave sleep, which is when growth hormone is released,” says Dr. Anne Marie Morse, a double board-certified neurologist and sleep medicine specialist and founder of DAMM Good Sleep. “That hormone is critical for recovery, metabolism, and preserving muscle mass.”
Another challenge: The specific types of foods that insufficient sleep makes us crave may cause sleep disturbances the next night. Studies have linked higher intake of saturated fat and lower intake of fiber with lighter, less-restorative sleep, and increased intake of sugar and carbohydrates with a higher incidence of sleep disturbances. Since weight gain and obesity can negatively impact quality of sleep, “This cycle of poor sleep and poor food choices can lead to a vicious cycle of weight gain and further sleep issues,” Dr. Ren-Fielding says.
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The good news: Improving your sleep even slightly could have a noticeable impact on weight loss. The first step in breaking a sleep loss cycle is to look at your sleep habits and think about ways that you can improve your sleep hygiene (the daily habits that set us up to get great rest). While maintaining a consistent bedtime is important, making yourself go to bed earlier may be the hardest place to start, since hitting the pillow before you feel sleepy can lead to anxious tossing and turning. Instead, look at your wake-up time as the first place to adjust your sleep-wake cycle. “To regulate your circadian rhythm, get out of bed at the same time each morning, even if you slept poorly,” says Jessica Fink, a sleep specialist in Austin, TX. “Our circadian rhythm determines the timing of sleep and wakefulness. Erratic rise times dysregulate this rhythm. It's like jet lag without the vacation.”
Once you’re up, try to spend some time outside in daylight (also important for regulating the circadian rhythm) and get in some physical activity, which can help you fall asleep sooner and sleep more soundly. “Good sleep starts in the morning,” Mermelstein says. “How you eat, move, and manage your day impacts your night. Get outside. Move your body. Eat enough during the day so you’re not crashing in the afternoon.” Then work toward sticking to a set sleep schedule during the week, and stay within one sleep cycle (90 to 110 minutes) of your bedtime or wake-up time on weekends.
Also helpful: Avoiding caffeine after 2 p.m., and dimming your lights and screen brightness in the hour before sleep time to boost the hormone melatonin and help induce sleepiness. (Visit the National Sleep Foundation for lots more specific tips.) The timing of your last meal can also have a big impact on sleep. “Pay attention to when you eat. Having an earlier dinner can significantly improve your sleep quality and help with weight control,” Dr. Ren-Fielding says. Some people with insomnia have success with a practice called sleep restriction, where you only get in bed during the hours you should be sleeping.
If you snore or struggle to fall asleep or stay asleep, make an appointment with your primary-care doctor or a sleep specialist, who may order a sleep study to assess whether you have sleep apnea or another sleep disorder. “The good news is that if it's diagnosed, sleep apnea can often be effectively treated with a CPAP machine,” Dr. Ren-Fielding says. “By improving sleep quality with a CPAP, a person's cortisol levels can decrease, reducing the cravings for sugary snacks and drinks, and leading to weight loss.” (Notably, losing weight can also help prevent sleep disorders; a 10-percent increase in body weight increases the risk of developing obstructive sleep apnea by 600 percent, according to the American Academy of Sleep Medicine).
Especially for people with obesity, weight loss itself can help reduce sleep disruptions and improve sleep health—a win-win cycle when it comes to weight management. “In my experience, improving sleep is one of the fastest ways to improve hunger control, mood, energy, and weight loss results,” says Dr. Hector Perez, MD, lead bariatric surgeon at Renew Bariatrics in Mexico. “If we tackled sleep first instead of last, we’d cut obesity rates faster than any fad diet ever could. As a bariatric surgeon, I’ve learned that if a patient’s sleep is broken, their metabolism usually is too. You can follow a perfect meal plan, exercise daily, even have surgery, but if you're consistently sleep-deprived, your body will fight fat loss every step of the way.”
