When you are watching your weight, the amount of sleep you get is almost as important as your diet and exercise and there is increasing evidence that sleep may be the missing factor for many people who are having difficulty losing weight.
So below are some of the reasons why ensuring you get enough sleep may help you lose weight.
Short sleep — usually defined as fewer than 7 hours — is linked to a higher body mass index (BMI) and weight gain.
One analysis of 20 studies including 300,000 people found a 41% increased obesity risk among adults who slept fewer than 7 hours per night.
In contrast, sleep was not a factor in the development of obesity in adults who slept longer (7–9 hours per night).
Another study found short sleep duration to be significantly associated with greater waist circumference, which is an indicator of the accumulation of belly fat.
In a recent review of 33 observational and intervention studies, short sleep duration was associated with an increased risk of obesity. Interestingly, for every additional hour of sleep, BMI scores decreased.
Though lack of sleep is only one factor, research suggests it negatively affects hunger levels, influencing us to consume more calories from high fat and high sugar foods.
Poor sleep increases the hunger hormone levels, (ghrelin), which makes you feel hungry, and decreases the satiety hormone, (leptin), which makes you feel full. Thus, you are driven to eat more and yet be less satisfied when you do eat.
Poor sleep may also negatively affect the sympathetic nervous system, resulting in increased levels of cortisol — a hormone related to stress. Elevated cortisol levels stimulate appetite with more cravings for sweet, fatty and salty foods.
It may also suppress various hormones, such as levels of insulin-like growth factor 1 (IGF-1). IGF-1 is linked to fat storage and metabolic syndrome.
Additionally, many sleep disorders, such as sleep apnoea, may get worse with weight gain. Unfortunately, this can lead to a cycle of poor quality sleep leading to weight gain and weight gain leading to poor quality sleep.
Poor sleep may increase appetite, probably due (as above) to its effect on hormones that signal hunger and fullness.
One review of studies found that those who experienced sleep deprivation consumed an additional 385 calories per day, with a greater than usual proportion of calories coming from fat.
Another study showed that sleep deprivation led to significant increases in hunger, food cravings, portion sizes, chocolate and fat intakes.
Getting a full night’s sleep may help you make healthier food choices. Lack of sleep alters the way your brain works and can affect decision making. This may make it harder to make healthy food choices and resist tempting foods.
In addition, it appears that the reward centres of the brain are more stimulated by food when you are sleep deprived. For example, one study found that sleep deprived participants had greater reward-related brain responses after viewing images of high calorie foods. Interestingly, they were also more likely to pay more for food than those who had adequate sleep.
Another study showed that sleep deprivation led to increased smell sensitivity to high calorie foods and greater consumption.
Thus, lack of sleep leads to poorer food choices, such as a higher intake of foods high in calories, sugar, and fat.
Poor sleep can increase your calorie intake by increasing late-night snacking, portion sizes, and the time available to eat.
Going to sleep earlier may help you avoid the late-night snacking that often comes with staying up past your ideal bedtime.
Pushing your bedtime later means you’re staying up longer, which creates a larger window of time for eating, especially if it has been many hours since dinner.
For example, if you ate dinner at 6:00 p.m. and you stay up until 1:00 a.m. every night, you’re likely going to feel like eating at some point between dinner and bedtime.
If you’re already experiencing sleep deprivation, you are also more likely to opt for less nutritious options.
Interestingly, late-night eating is associated with greater weight gain, a higher BMI, and decreased fat oxidation — making weight loss more difficult.
What’s more, eating large meals too close to bedtime, may decrease the quality of your sleep and make your sleep deprivation even worse. In particular, those with acid reflux, indigestion, or sleep disorders may want to limit food intake before bed.
Ideally, try to limit your food intake 2–3 hours before bed and if you’re genuinely hungry, consider having a small, protein-rich snack, such as Greek yoghurt or cottage cheese.
Getting enough sleep may help you avoid decreases in metabolic rate that can happen when you haven’t gotten enough sleep.
Your resting metabolic rate (RMR) is the number of calories your body burns when at rest.
Lack of sleep may also suppress fat oxidation, which is the breakdown of fat cells into energy.
Poor quality sleep can decrease muscle synthesis, which itself may lower RMR.
One small study showed muscle synthesis decreased significantly by 18% and plasma testosterone by 24% after one night of poor sleep. Additionally, cortisol significantly increased by 21%. Collectively, these conditions contribute to the breakdown of muscle. However, this study was small and only 1 day long, which limits the credibility of the conclusions.
Sleep and physical activity have a close two-way relationship. A lack of sleep decreases physical activity, and lack of physical activity may lead to worsened sleep.
Numerous studies have shown that regular exercise can decrease the time it takes you to fall asleep and improve the overall quality of sleep across all age groups.
Furthermore, a lack of sleep can cause daytime fatigue, making you less motivated to exercise and more likely to be sedentary.
In turn, you may expend fewer calories in a day when sleep deprived than you would after a proper night’s rest. This can make achieving a calorie deficit for weight loss more difficult.
What’s more, a lack of sleep can negatively affect your athletic performance by decreasing your reaction time, fine motor skills, muscular power, endurance and problem solving skills.
It may also increase your risk of injury and delay recovery so clearly getting enough sleep is critical to being able to stay active.
In summary, it would seem that economising on sleep has many unhelpful consequences for weight management and is probably as important to consider along with diet and exercise.
Like many lifestyle factors, ensuring that you get enough sleep really starts with developing better habits – focussing on sleep hygiene is a logical first step.
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