Most people get around eight hours of sleep and, of course, aren't eating when they are doing so. Our bodies still need to burn calories to function, however, just to maintain basic bodily processes, such as breathing and cell production. Add those expended calories to the water weight lost through respiration and perspiration and you have a bit of weight loss. Although you will gain that weight back once you start eating and drinking, getting a good night's sleep will also help control your appetite and satiety.
Basal Metabolic Rate
The rate at which you burn calories when at rest is referred to as your basal metabolic rate, or BMR, and it reflects what you need to perform basic bodily functions such as keeping your heart beating. The BMR varies from person to person according to size, sex and weight. Heavier people burn more calories, as do males, and people lose fewer calories when they age. According to the Mayo Clinic, your BMR burns between 65 to 75 percent of your total calories. When you sleep, your BMR slows down a bit but fluctuates throughout the night. Although how many calories you burn depends primarily on your BMR, most people burn around 77 calories an hour a night when sleeping, according to Fitday.com.
Fluids
Burning calories isn't the only way you drop weight while sleeping; you also lose a certain amount of fluids through respiration and transpiration and movement of water through the cells. When you exhale, you breathe out a small amount of water. The same goes for transpiration, which is another way of describing the sweating process. The body also takes excess fluids it has accumulated through the day and moves them into the cells. The water is then disposed of through the kidneys by urinating, which often happens the first thing in the morning after sleep.
Total Weight Lost
How much actual weight you lose when sleeping will depend on several factors including your BMR and how much food or fluids you had right before you went to sleep. If you ate right before bedtime, your body will take calories from the food you ate and you won't lose as much. This is why experts recommend eating a few hours before bedtime. To get an idea of how much weight people lose under ideal circumstances of sleep, a study was done by Dr. Walter Moraes of Universidad Federal Sao Paolo, Brazil. Dr. Moraes studied 14 healthy men age 21-30 while they were asleep for eight hours as well as while they were awake in bed for eight hours. He found that the men lost about a 1/4 lb. each hour, or about 2 lbs. a night, when sleeping eight hours. Interestingly, Moraes found that they lost three times less than when they were in bed but awake.
Sleep and Weight
How much sleep you get not only contributes to how much weight you lose when sleeping, it is also a factor in your waking hours. Lack of proper sleep influences our hormones, particularly leptin, ghrelin and cortisol. When you don't sleep enough, leptin, which gives you the feeling of being full, gets higher, and ghrelin, which makes you feel full, lowers. This increases your appetite and makes it more difficult to feel fully satisfied. Cortisol levels also increase, which means you crave high-carbohydrate foods that can easily lead to weight gain if consumed in too large a quantity. There is no precise amount of sleep that is best for everyone, but it's recommended to get at least seven and a half hours a night to keep the hormones in balance.
References
- Scientific American: You Snooze, You Lose--Weight; Christina Frank; October, 2009
- Psychology Today: Lose Weight While You Sleep (For Real!); Dr. Dennis Rosen; June, 2009
- KidsHealth.org: Why Do I Weigh Less in the Morning?: Dr. Mary L. Gavin; May, 2010
- FitDay.com: Are Calories Burned During Sleep?
- University of Tsukuba, Ibaraki, Japan: Metabolic Rate And Fuel Utilization During Sleep Assessed By Whole-Body Indirect Calorimetry; Katayose et. al.; July, 2009
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