Why Do I Lose Weight While I Sleep?

At night, it is possible to lose two to three pounds during sleep. Stockvisual / Getty Images

The main thing that is changing overnight is the amount of water in your system. It's amazing how much water weighs! A gallon of water weighs 8 pounds, and a pint of water (16 ounces) weighs 1 pound (in metric, 1 liter of water weighs 1 kilogram). This means that if you drink a 1-liter bottle of soda, you instantly gain 1 kilogram (2.2 pounds) from the water! That's a big weight change, and it can happen very quickly.

Overnight, there are two processes that cause you to lose water gradually. The first is respiration. Each time you exhale, you lose a little bit of water (exhale onto a cool piece of glass and you can see this moisture). The second is transpiration through the skin, also known as sweating. Over the course of a night, both of these processes eliminate quite a bit of water.

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Then there is the tradition of using the restroom prior to the morning weigh-in. That process can eliminate up to 1 pound (0.5 kilograms) of water.

According to this water information page, the average person eliminates about 1.2 liters of water in urine each day, and also eliminates about 1 liter a day through perspiration and respiration. That's 2.2 kilograms (almost 5 pounds) of weight fluctuation happening throughout the day!

You may have heard that it's important to drink about eight glasses of water every day. Respiration, transpiration and urination are the reasons why!  See the next page to learn more.

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Originally Published: Sep 24, 2009

Lose Weight Sleeping FAQ

Can you lose weight by sleeping?
Getting proper sleep isn't going to cause you to lose fat, though it’s common to lose water weight overnight. You need a proper diet and exercise for that. However, high-quality sleep can help you avoid excess weight gain.
What is the healthiest sleeping position?
Resting on your side, with your spine kept straight can help you get a good night's sleep and lower the chances of sleep apnea.
Is seven hours of sleep enough for weight loss?
Doctors recommend that you sleep seven to nine hours every night for the body to be healthy and avoid the side effect of weight gain. When you don’t sleep enough, you’re more likely to eat high calorie foods and have a reduced ability to resist unhealthy snacking and sugary foods.
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