When it comes to weight loss, diet and exercise are usually thought of as the two key factors that will achieve results. However, sleep is an often-neglected lifestyle factor that also plays an important role.
The recommended sleep duration for adults is seven to nine hours a night, but many people often sleep for less than this. Research has shown that sleeping less than the recommended amount is linked to having greater body fat, increased risk of obesity, and can also influence how easily you lose weight on a calorie-controlled diet.
Typically, the goal for weight loss is usually to decrease body fat while retaining as much muscle mass as possible. Not obtaining the correct amount of sleep can determine how much fat is lost as well as how much muscle mass you retain while on a calorie-restricted diet.
One study found that sleeping 5.5 hours each night over a two-week period while on a calorie-restricted diet resulted in less fat loss when compared to sleeping 8.5 hours each night. But it also resulted a greater loss of fat-free mass (including muscle).
Another study has shown similar results over an eight-week period when sleep was reduced by only one hour each night for five nights of the week. These results showed that even catch-up sleeps at the weekend may not be enough to reverse the negative effects of sleep deprivation while on a calorie-controlled diet.
Metabolism, appetite, and sleep
There are several reasons why shorter sleep may be associated with higher body weight and affect weight loss. These include changes in metabolism, appetite, and food selection.
Sleep influences two important appetite hormones in our body – leptin and ghrelin. Leptin is a hormone that decreases appetite, so when leptin levels are high we usually feel fuller. On the other hand, ghrelin is a hormone that can stimulate appetite and is often referred to as the “hunger hormone” because it’s thought to be responsible for the feeling of hunger.
One study found that sleep restriction increases levels of ghrelin and decreases leptin. Another study, which included a sample of 1,024 adults, also found that short sleep was associated with higher levels of ghrelin and lower levels of leptin. This combination could increase a person’s appetite, making calorie-restriction more difficult to adhere to, and may make a person more likely to overeat.
Consequently, increased food intake due to changes in appetite hormones may result in weight gain. This means that, in the long term, sleep deprivation may lead to weight gain due to these changes in appetite. So getting a good night’s sleep should be prioritized.
Along with changes in appetite hormones, reduced sleep has also been shown to impact on food selection and the way the brain perceives food. Researchers have found that the areas of the brain responsible for reward are more active in response to food after sleep loss (six nights of only four hours’ sleep) when compared to people who had good sleep (six nights of nine hours’ sleep).