People can lose one to one and a half pounds of water while sleeping. That is why, if you desire the lowest number on the scale, it is best to weigh yourself first thing in the morning! Breathing, sweating, and even waking up in the middle of the night to pee all contribute to fluid loss. Men lose about 1 pound (0.5 kg) per night and women lose about 2 pounds (1 kg).
When you wake up in the morning, your body is actually being re-hydrated from the fluids that were lost during sleep. In other words, you're thirsty when you wake up because there's water in your body that was not there when you went to sleep.
The good news is that most of this water loss is through urine and stool. The bad news is that some of it is through sweat which means you'll be smelling pretty ripe by the time you get out of bed.
During sleep, our bodies use up lots of energy: building muscles, thinking, moving our eyes, and so on. This energy needs fuel, so we produce more of the chemicals that provide this energy, such as glucose for blood sugar or fatty acids for muscle contraction. These fuels are then used by cells to make new tissue, so they're also called "anabolic" drugs because they help build up our bodies.
Your body is composed of around 55-75 percent water, which accounts for a substantial percentage of your weight (2, 3). According to some estimates, water loss may account for more than 80% of nighttime weight loss. However, how much weight you lose when sleeping depends on your body composition and metabolic rate (4).
If you have a large amount of muscle tissue, you may be able to maintain your blood volume at a constant level while asleep, thereby preventing water loss from through your skin (5). Also, if you are a male who averages around 10 pounds per night, you can assume that most of this loss is due to water being released through the muscles as they relax during sleep (6).
For females or males who do not have a large amount of muscle tissue, nightly water loss through the skin will likely be the case and could lead to excessive daytime urinary output and reduced plasma volume. These changes can affect how well you perform tasks/exercise the next day.
So yes, you can lose water weight overnight - but only if it's due to muscle relaxation and not your blood volume or other factors mentioned above.
While no one claims that drinking water before bed (or at any other time of day) would make you lose weight, there is evidence to support the water-weight loss connection: After all, water makes up 60% of your body, so the clear, calorie-free drink is involved in almost every physical function. Drinking enough water may also help you feel full after eating, thus reducing your appetite for food overall.
The best way to lose weight is through a healthy diet and regular exercise program. However, if you're finding it difficult to reduce late-night snacks or want an additional tool for weight loss, then drinking water before bed could be just what you need.
By drinking enough water each day, you can help release toxins out of your body through your urine and sweat and get rid of fat cells from head to toe. Also, research shows that people who drink more water tend to eat less overall. So by simply adding more "water days" to your week, you can take care of your waistline and your skin from head to toe.
Of course, you cannot lose weight by drinking water alone. You also need to change your diet and adopt a healthier lifestyle overall if you want to see real results. But if you are finding it difficult to resist the urge to eat something sweet or heavy later in the night, then drinking water first could be the solution you've been looking for!
Given that a quart of water weighs around 2 pounds, that's 3-4 pounds of water weight removed in an hour! According to a Hammer Nutrition article, we might be losing even more! "Per hour of activity, you lose around one liter (34 ounces) of fluid. Extreme heat and humidity can quickly increase the amount to three liters."
That's about 6% of your body weight! So if you're 75 pounds, that's 45 pounds lost during exercise in extreme heat. But you need to drink enough to replace that loss.
In general, you should try to replace those fluids every hour. This means drinking plenty of water or other appropriate liquids. Some examples are sports drinks, sugary juices, coffee, tea, soup, and so on.
If you don't drink enough, you'll become dehydrated. Dehydration makes you feel tired, irritable, and unable to function at your best. It also increases your risk of heart attack and stroke. Drinking too much can cause diarrhea, nausea, headaches, dizziness, excessive thirst, and urination, among other problems.
So make sure you're drinking enough during exercise in hot conditions. In addition to being aware of your own needs, pay attention to what and how much your teammates are drinking as well. You want them to stay healthy too!