4 Reasons Sleep Is So Important for Weight Loss

While every weight-loss program or diet has its own nuanced take on the process, the basics are generally the same and involve trimming calories while increasing exercise. But most plans neglect one key variable: your sleep.

Most of us need at least seven hours of sleep each night, but more than a third of American adults aren't hitting that minimum on a regular basis, according to the Centers for Disease Control and Prevention. Yet sleep is crucial for healthy body function and can affect your hormones, gut health, fat storage process and even your decision-making abilities — all of which can influence the number on the scale.

So, if you're following that diet plan to a T and hitting the gym regularly but aren't prioritizing quality rest, here's what you should know about how sleep (or lack thereof) might be affecting your weight-loss goals.

How much sleep you get influences your body's production of the hormones leptin and ghrelin.

Leptin is a hormone that your body releases to increase your satiety, according to the Hormone Health Network. Leptin regulates your food intake and energy expenditure, helping your body maintain its weight.

Restricting sleep, however, can decrease the body's leptin levels, says Cynthia Li, MD, an integrative and functional medicine doctor based in Berkeley, California. In turn, your appetite goes up, which can cause you to overeat. That's why a late night may leave you feeling less satisfied after lunch and reaching for the snack cabinet more frequently.

While your leptin levels decrease with sleep deprivation, your ghrelin levels go up, according to Lisa Alex, MD, a primary care physician with the Medical Offices of Manhattan. Ghrelin is a hormone that increases feelings of hunger, causing your body to crave and consume more calorie-rich food in attempt to compensate for your lack of energy.

Lack of sleep can also increase the levels of cortisol in the body, a hormone associated with stress, says Dr. Li. Chronically elevated cortisol can not only increase your hunger but may also negatively affect your body's metabolism, according to a November 2015 study published in ‌Sleep Science‌.

The increase in cortisol caused by restricted sleep can also affect where your body stores fat, says Dr. Li. In a state of sleep deprivation, you tend to store more fat in the belly. "This belly fat, called 'VAT' (visceral adipose tissue), in turn releases inflammatory chemicals, which stimulates more cortisol," says Dr. Li. (Talk about a vicious cycle.)

Even just a few days of sleep deprivation can affect how your body stores fat from food, according to a September 2019 study published in the ‌Journal of Lipid Research‌. After comparing blood samples, researchers found that sleep-restricted participants maintained less fat in their bloodstreams after a meal. This means the body hoards or stores fat more quickly when sleep-deprived, explains Dr. Li.

Cutting back on your sleep can also reduce the benefits of diet and exercise, according to a small October 2010 study published in the ‌Annals of Internal Medicine‌. When you restrict calories in a sleep-deprived state, your body loses more lean muscle mass than fat. Ultimately, this renders your diet less effective, as muscle burns more calories than fat, even at rest, according to the Mayo Clinic.

Just as your weight can be affected by your hormones, weight loss can be hindered by your gut. Your gut microbiome (the trillions of bacteria, viruses, yeast and fungi in your gut) plays a big role in digestion and processing food, drugs, hormones and brain chemicals, according to Dr. Li. Therefore, this friendly bacteria community is important when it comes to weight maintenance.

Gut health can be compromised in those who are active during the night, according to a September 2019 study published in ‌Nature‌. Sleep deprivation affects your circadian rhythm (your body's internal clock, which regulates your sleep), which can damage your gut.

Sleep deprivation and gut health affect one another cyclically. Even short intervals of sleep deprivation can alter your gut flora, according to Dr. Li. This increases inflammation in the body, which can then cause you to lose even more sleep.

Sleep can not only influence your feelings of hunger and fullness, but it may also affect the type of food you crave. Sleep deprivation activates parts of the brain associated with motivation and reward, which can intensify food cravings, especially for unhealthy foods, according to a March 2016 study published in ‌Sleep‌.

Sleep deprivation also negatively affects the prefrontal cortex of the brain, which is responsible for impulse control and helping you make healthy decisions, according to Dr. Alex. So, not only can sleep deprivation cause you to crave more unhealthy foods, but it also can impair your ability to resist indulging in them.

"In studies looking at acute sleep deprivation and food choices, people with less sleep opted more for high-calorie junk foods," Dr. Li says. "This makes sense — that we would crave 'easy energy' when our bodies feel tired."

"Easy energy" foods are often also comforting. When cortisol spikes (like when you skimp on sleep), comfort foods seem to dampen feelings of stress, according to Harvard Health Publishing, which may also cause you to crave more unhealthy foods.

Occasionally, we're all guilty of checking our email before bed or staying up to watch just one more episode of our favorite show. But kicking some bad habits and optimizing your evening routine can help improve your sleep and set you up for successful weight loss.

Your body needs time to switch to night mode, so be sure to give yourself enough time to wind down. Practice a relaxing bedtime ritual (like stretching or journaling) and avoid using bright light in the few hours before your head hits the pillow, advises the National Sleep Foundation. Set the temperature in your bedroom between 60 and 67 degrees and avoid alcohol or nicotine in the evening.

If you continue to struggle with your sleep or experience insomnia, consider speaking with your doctor or a sleep professional. For some, even keeping a sleep diary can help bring attention to some bad sleep habits you may be practicing without realizing it.