How Much Weight Do You Lose During Sleep?

When you step on your scale after a night’s sleep you might not like what you see, but chances are those are the smallest numbers your scale is going to show you on that day. Most people weigh their lightest first thing in the morning. If you want to know exactly how much weight you lose each night, weigh yourself right before you go to sleep and then again after you’ve awakened. What’s more interesting, perhaps, than how much weight you lose, is where it goes and how much of it is true weight loss.

Sleep Weight Loss

People lose weight when they sleep; even more than when they are resting awake, according to a study by Dr. Walter Moraes of Universidad Federal Sao Paolo, as reported in Psychology Today. Moraes presented the results of his study at the 2009 Associated Professional Sleep Society. He confined 14 healthy men to a bed with a built-in scale for 16 hours. The men didn’t urinate or defecate during the study. While sleeping, they lost 1.9 g per minute, about 1/4 lb. per hour, which amounts to 2 lbs. over eight hours of sleep. While resting awake in bed, they lost 0.6 g per minute.

Respiration Weight Loss

Moraes' study doesn’t account for why his subjects lost weight. Much of the weight lost during sleep is water weight that disappears through respiration and perspiration. You regain this weight as you drink fluids during the day. Your lungs require moisture to function properly, so the air you exhale contains water. Exhale on to a mirror and you’ll see the moisture. During an autumn day, you lose 3 to 4 cups of water through breathing, according to naturopathic physician Jennifer Brett. That amounts to as much as 2 lbs. of water. During the winter, when it’s much dryer, you can lose an additional pound. On a dry winter night, you can lose 1 lb. of water breathing while you sleep.

Perspiration Weight Loss

On a typical day, the average person loses 1.0 to 1.5 lbs. of water by sweating. Depending on how hot you keep your bedroom and how thick you layer your blankets, you might lose as much as 1/2 lb. sweating at night. Add this to water lost during respiration, and you get an average total water loss of 1.5 to 2.0 lbs. each night. If you get up to use the bathroom during the middle of the night, add more fluid loss to your total.

Sleeping Metabolism

The 2 lbs. of weight loss that occurred while Moraes' subjects slept could have come chiefly from water weight, which is best viewed as weight fluctuation and not true weight loss. However, you do burn calories while you sleep. Your basal metabolism rate refers to the number of calories your body uses to operate while sedentary, and it includes energy consumed operating and maintaining your heart, lungs, brain and other organs. When you sleep, your heart rate and respiration decrease and digestion slows. Your metabolism during sleep decreases to an average of about 80 percent of your BMR. A 2009 study in the journal Metabolism reports that overall energy consumption decreases for the first half of the night, reaching a low of 65 percent of the BMR, and then remains stable until awakening. The average BMR for women is around 80 calories per hour and for men around 115 calories per hour, which, at an average sleeping metabolic rate of 80 percent of the BMR, means a woman burns about 512 calories while sleeping and a man burns about 736 calories. Consequently, an average woman burns about 1 lb. a week sleeping, and a man burns about 1 lb. every five days while sleeping.