On average, you sweat about 25ml per hour of sleep under temperate conditions (around 85 degrees Fahrenheit). ² If you sleep for an average of eight hours, that's around 200ml of sweat per night. This would equate to a drop in weight of approximately 200g overnight.
One study found that sleeping 5.5 hours each night over a two-week period while on a calorie-restricted diet resulted in less fat loss when compared to sleeping 8.5 hours each night. But it also resulted a greater loss of fat-free mass (including muscle).
As you sleep, your body burns calories, causing you to lose between 1 to 4 pounds of your weight overnight; this weight loss can be regarded as temporary weight loss because you need to consume fewer calories than you burn to avoid weight gain.
You Lost Water Weight
When we break down these molecules, we release water—which is excreted through our urine and sweat, which is what causes the weight loss you experience in your sleep. This effect can be substantial if you're low-carb sleeping or not drinking much water throughout the day.
Sleeping naked has a slew of health benefits, including helping you to lose weight. A study conducted by the US National Institutes of Health found that keeping yourself cool while you sleep speeds the body's metabolism because your body creates more brown fat to keep you warm.
The answer is a scientific “No!” Because a pound of fat contains 3500 calories, and most people don't burn even that number each day, you would need to consume “less than zero” calories to lose that much weight in fat.
You're Dehydrated
Dehydration causes your body to retain excess water, which can lead to 5 pounds of weight gain overnight (5). When you feel thirsty and drink a lot of fluid at once, you'll absorb the extra fluid quickly and it shows up on the scale within 24 hours.
In some people, especially those who have been dieting or fasting, a meal high in carbohydrates, such as pasta or rice, can be stored as glycogen. Glycogen is stored with water, which causes an individual to gain water weight very quickly – as much as 2 pounds overnight.
Instead, choose casein protein if you want to boost your overnight fat burning. Casein is a gradually digested protein that can take your body around six to eight hours to break down. This means your metabolism will be kept active throughout the night, and you'll wake up feeling energetic instead of starving.
“Everyone's weight fluctuates throughout the day, and especially from morning to night,” says dietitian Anne Danahy, MS, RDN. “The average change is 2 to 5 pounds, and it's due to fluid shifts throughout the day.” If you see fluctuations of less than 5 pounds, you needn't worry.
Most of your overnight weight loss can be attributed to the water you lose through sweating and breathing.
New research, published in 2022, found not getting enough sleep led to an increase in calorie intake, body fat, and belly fat. The researchers found people who slept four hours a night had a 9% increase in subcutaneous belly fat and an 11% increase in abdominal visceral fat, compared to those who slept 9 hours a night.
Fasting for a certain number of hours each day or eating just one meal a couple days a week, can help your body burn fat. And scientific evidence points to some health benefits, as well.
According to the National Sleep Foundation, people who sleep for less than five hours a night are almost a third likelier to gain weight (30 pounds over the course of 16 years) than those who get seven hours of sleep each night.
Unintentional weight gain occurs when you put on weight without increasing your consumption of food or liquid and without decreasing your activity. This occurs when you're not trying to gain weight. It's often due to fluid retention, abnormal growths, constipation, or pregnancy.
You should step on the scale first thing in the morning. That's when you'll get your most accurate weight because your body has had the overnight hours to digest and process whatever you ate and drank the day before. And you should try to turn that step into a regular part of your routine.
“Your weight won't be consistent if you weigh yourself on Friday and Monday,” she says. “Many people have a different routine on the weekends. They might eat out more, drink alcohol or snack more. Compare that to Friday, if you've been eating consistently for five days, and you'll see a big difference.”
Daily weigh-ins.
If you're really committed to losing weight, weighing yourself every day can be helpful. Research shows that people who weigh themselves every day have even more success with weight loss than those who weigh in once a week.
Overeating one day will not have much impact on your weight, but it will surely leave you feeling bloated. You can have an extra slice of your favorite cheesecake occasionally, but do not make this your habit. The next day, return to your fitness routine and everything will be fine.
Excess fluid will typically take a couple of days to flush out, but it depends on how much water you're retaining and what you decide to do about it (just let it work itself out or try one of the methods listed in this article).
Generally to lose 1 to 2 pounds a week, you need to burn 500 to 1,000 calories more than you consume each day, through a lower calorie diet and regular physical activity. Depending on your weight, 5% of your current weight may be a realistic goal, at least for an initial goal.