Drinking a large glass of water on an empty stomach can make your body burn a few extra calories, especially if you're overweight, because it tricks your cells into thinking they're hydrated and need to work harder.

When overweight or obese people drink a glass of water on an empty stomach while sitting still, their body burns a few extra calories, possibly because the water makes their cells swell and wake up their metabolism.

For people who are overweight, drinking a glass of water on an empty stomach can slightly boost calorie burning, but this doesn’t happen in people with normal weight.

When overweight people on a diet drink more than a liter of water a day, they tend to lose more weight—even if they don’t eat less—possibly because water helps their body use insulin better and reduces cellular stress.

If overweight people drink more than a liter of water a day while eating less, they lose more weight — even if they’re not eating fewer calories overall — possibly because their insulin levels drop and their body burns fat better.

If you're trying to lose weight and you drink over a liter of water every day, you might lose more weight—even if you're eating the same amount—because it helps your body manage insulin and stay hydrated.