The Two-Way Relationship Between Weight and Sleep

If you’re used to squeaking by on minimal sleep, you’re hardly alone. According to the Centers for Disease Control and Prevention (CDC), about one-third of US adults don’t get the recommended seven hours of sleep per night.

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But rest is always a worthwhile priority. Vital processes, such as memory consolidation, tissue repair and hormone production, occur after your body powers down. While a night of poor sleep here and there might not have major consequences, regularly skimping on sleep is associated with a spate of health issues, including obesity and weight gain. The relationship is bidirectional: Being underslept can contribute to weight gain and impede weight-loss efforts, and being overweight can make it harder to get a good night’s rest.

Courtesy of sleep research, here are six things to understand about the two-way street between sleep and weight.  

Sleep loss can throw your hormones out of whack         

Two of the main appetite-regulating hormones are leptin, which tells your brain when you’re full, and ghrelin, which signals hunger. They’re both tied to your circadian system (aka your body clock), which means levels of these hormones should rise and fall at the same times each day. But sleep loss interrupts their normal daily patterns. Multiple studies have associated insufficient sleep with increased levels of ghrelin and reduced levels of leptin, and corresponding increases in hunger and appetite.  One 2022 study found that ghrelin levels increased after just one night of sleep deprivation, and that the effect was stronger in those with obesity.

There’s also evidence that short sleep duration impairs insulin, a key metabolic hormone. Studies have found that even short-term sleep deprivation (e.g., sleeping four to five hours for five nights in a row) has been associated with reduced insulin sensitivity (aka insulin resistance). This means that your cells become less responsive to insulin, requiring you to make more of it to control blood sugar levels. Insulin resistance can lead to high blood sugar and, if the issue becomes chronic, to prediabetes and even Type 2 diabetes. And, in an effort to lower blood sugar levels, your body begins to store extra sugar in your fat cells, which contributes to weight gain. 

You make worse food choices when you’re underslept

Eating habits change for the worse when people don’t sleep enough, according to a 2022 review paper that analyzed the results of 10 studies. Insufficient sleep, the review determined, can lead to greater consumption of a variety of unhealthy foods, including fast food, sweets, and foods high in saturated fat such as bacon and whole-fat dairy products. Consumption of fruits and vegetables, by comparison, goes down. Another study showed that people who log less than 5.5 hours of sleep are more likely to snack on high-carb snacks compared to those getting 8.5 hours. To state an obvious but important point, sleeping less in a given 24-hour period means more time for eating. 

Food choices can also affect how people sleep. In one 2016 study, researchers found that eating foods high in saturated fat or low in fiber led to lighter, less restorative sleep. In addition, consuming sugar and non-sugar carbs affects sleep quality by causing nighttime arousal. 

Consistent nighttime sleep is optimal for weight management

In studies, shift work has been associated with health issues including abdominal obesity. One issue with sleeping during waking hours, research suggests, is that people simply end up sleeping less. Even though shift workers are more likely than others to get extra sleep on their days off, those additional Zzzs may not compensate for an overall sleep deficit (and we already know that getting enough sleep helps weight management). A 2023 review found that shift workers have similar energy intake as non-shift workers, but that people gain more weight when they eat during nighttime hours, versus eating the same amount and types of foods during the day. Evidence from animal research echoes these results by showing that keeping irregular hours can cause weight gain via a desynchronized body clock. If you have an inconsistent work schedule, experts recommend taking a nap before or during your shift (if possible) and paying close attention to your food choices while working.

Late-night noshing impedes weight loss 

Research has found that eating a late dinner or snacking before bedtime can lead to weight gain. Animal studies suggest that eating during nighttime hours leads to more weight gain than eating during the day. This remains true even when calorie intake and activity levels during waking hours are similar. Because of this, researchers suspect that when you eat — not only what you eat — affects weight gain or loss. In other words, it’s better for your waistline to have a snack at 2 pm than 2 am. 

Snoozing is key for fat loss

A lack of sleep leads to a slower metabolic rate, meaning that you burn fewer calories throughout the day. This is evident from multiple studies where people who slept less, usually less than 5.5 hours per night, burned less fat than those who got over 8 hours of sleep. 

When you stay awake longer, you do burn extra calories — about 100 more, according to a 2023 comprehensive review study. But under-slept people also tend to consume more calories than their well-rested counterparts. One study found that people who sleep less than four hours per night consume 200 to 500 more calories per day than those who log seven to nine hours.

Sleep quantity isn’t the only metric that matters  

When it comes to sleep and its impact on weight, both how much and how well you sleep are important. Weight-loss success has been associated with longer sleep duration as well as better sleep quality.

Many studies have found that it’s easier to lose weight when a higher percentage of your night is spent in deeper sleep stages. The opposite relationship is true too – there’s a well-supported link between poor sleep quality and high body weight. Sleep disruptions can promote weight gain, both by impairing hormone functioning and by causing your body to break down carbs for energy instead of fat. What’s more, obesity and weight gain are risk factors for multiple sleep disorders, including sleep apnea, defined by repetitive pauses in breathing, and restless legs syndrome, defined by an urge to move your legs that typically sets in at nighttime. 

Sleep quality and quantity are often interrelated. For instance, if it takes you two hours every night to fall asleep, that’s a sleep quality issue — but it probably also means you’re not hitting your seven-hour nightly sleep goal. So how can you tell if your sleep quality is up to snuff? Experts often use the Pittsburgh Quality Sleep Index, a questionnaire that assesses different aspects of sleep, including:

  • Sleep latency, meaning how long it takes to fall asleep (20 minutes or less is ideal)
  • Sleep efficiency, meaning the percentage of time in bed spent asleep (vs. lying awake)
  • Sleep disturbances, such as a nightmare, snoring or anything else that interrupts your sleep   
  • Daytime functioning

If you’re dealing with recurring sleep problems — whether you can’t fall asleep, can’t stay in a deep sleep, or fall asleep at the wrong hours — talk to your healthcare provider, who can determine if you’ll benefit from treatment. 

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