Think to yourself for a moment — on average, how many hours do you sleep per night?

According to a report put out by the World Association of Sleep Medicine, the majority of Canadians are sleep deprived. 60% of adults feel tired most of the time, getting an average of 6.9 hours of sleep per night, with the recommended being 8 [1]. The same trend continues in the United States and most modern societies.

Everyone knows that sleep is important, but the reality is that not many of us actually get what we need. We’re too busy with work, family, sports, or even just Netflix, to give our body’s the rest they need. But if you’re looking to improve your body composition and your overall health, getting enough sleep is critical.

Why is sleep important?

Sleep is the time when the body repairs itself. It gives us an opportunity to relax, shut down body systems into low power mode, and focus on repair and restoration. Specifically, here are 7 reasons why adequate sleep is key:

1. Improves productivity, concentration, and memory
2. Maximizes athletic performance
3. Improves immune function
4. Decreases risk of developing heart disease and stroke
5. Improves glucose metabolism and decreases risk of type 2 diabetes
6. Decreases levels of inflammation
7. Boosts mood

But the one other thing that sleep is incredibly important for is maintaining a healthy weight and body composition. As sleep regulates our hormones, lack of sleep can cause imbalances, which may result in weight gain.

How sleep and weight are related

Poor or inadequate sleep is one of the leading risk factors in the development of obesity. Studies have shown that both children and adults with short sleep durations are significantly more likely to become obese [2, 3].

But why is this?

Our bodies are largely controlled by hormones — chemical messenger secreted by endocrine glands that influence most major body functions, which includes how we use and store energy. They also mediate the interactions between sleep, metabolism, and BMI.

The two main hormones that control our hunger, leptin and ghrelin, are highly influenced by sleep patterns. Leptin is a hormone that is released from fat cells that signals to the brain, the hypothalamus specifically, that you have enough energy and don’t need to eat; it functions mainly to prevent humans from starvation of overeating. The other hormone, ghrelin, is an appetite-increasing hormone that’s function is regulated primarily by food intake; it acts on the hypothalamus, as well, to stimulate hunger.

A study conducted on the impact of sleep on body composition showed that levels of ghrelin were higher in individuals with short sleep, while levels of leptin were lower [4]. Short-term sleep restriction lowers levels of leptin, which in turn increases levels of ghrelin [5]. When you don’t sleep enough, cortisol levels also increase. Cortisol is the stress hormone that is frequently associated with fat gain, but it helps to activate reward centers in your brain that make you crave food, too. A combination of high ghrelin and high cortisol inhibits communication to the areas of the brain that leave you feeling satisfied after a meal [6], meaning you’re never quite feeling full and continue to crave low quality foods.

Combining all of these factors, we leave ourselves at a higher risk for gaining weight and being unable to lose it.

Additionally, hypothalamic-pituitary functions that control eating habits, energy balance, and metabolism are all tied to circadian rhythms, meaning they are highly integrated with sleep regulation processes. Experiments have demonstrated that lack of sleep has important effects on cortisol levels, glucose tolerance, and growth hormone secretion [7]. Therefore, when hormone balance is off, we put ourselves at higher risk for weight gain because we are tired.

Putting it all together

Not only does lack of sleep affect your body’s basic functions, but it also probably means your energy levels aren’t quite as they should be. When we have low energy, we are less productive and have less motivation to partake in activities, whether that be the gym or simply doing work around the house. And we all know that lack of movement and activity is a large contributor to weight gain.

So while we may fall off the proper sleep train every now and again, it’s crucial to get your sleep habits under control. Limit exposure to blue light 2-3 hours before bed, ensure your room is at a slightly cooler temperature, make sure there are no lights around, and relax the mind and body — all of which prepare the body for a deep, relaxing, and restorative sleep.

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