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The Science Behind Why Water Is Good for Weight Loss

A man is sitting on a bench in a stadium, wearing athletic attire. He has a towel over his shoulder and is drinking from a water bottle. The science behind hydration for weight loss seems to resonate with the mostly empty seats behind him. MyFitnessPal Blog
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We all know that hydration is important — especially in the scorching summer months. Getting your standard eight glasses a day can help you stay cool, hydrated and energized through even the most intense sweat-inducing heat waves.

But drinking plenty of water can also be a super easy — and more importantly, super effective — way to lose weight, according to the experts.

To look at exactly what drinking more water does to your stomach, appetite and brain, researchers from the Society for the Study of Ingestive Behavior took MRIs of participants’ stomachs and brains after they had ingested either a small glass of water (about 2 fluid ounces) or a large glass of water (about 12 fluid ounces).

The MRI scans showed that the participants who drank more water doubled their stomach volumes and showed increased activity in the brain. But more importantly, the participants reported feeling fuller.

In other words, water helps to stave off hunger: The more you drink, the less room you have for consuming calories.

Water can also aid weight loss in a second way, says Keri Gans, RD, author of The Small Change Diet. “A lot of times people think they’re hungry when in reality they’re just slightly dehydrated,” she says. “If you’re staying hydrated, you’re less likely to mistake thirst for hunger.”

How Much You Should Drink

So how much water do you actually need to be drinking to reap the hunger-busting benefits? According to Gans, it all depends on how much you weigh: Divide your weight in half, and that corresponds to the number of ounces of water per day you should be drinking. For example, a woman who weighs 135 pounds should be getting 67 ounces per day, or about eight glasses.

However, you also need to take into consideration your activity level and the temperature outside. “On a very hot day, that ideal number of ounces is going to go up,” says Gans. Whether you’re lounging at the beach or going for a bike ride in the sun, make sure you add a couple of glasses to your regular intake. “If we’re losing water, we need to be replenishing it,” she says.

How to Drink More

Luckily, there are plenty of ways to use water as a weight-loss tool beyond just toting around a water bottle everywhere you go — although that’s not a bad idea. “You shouldn’t wait until you feel thirsty to drink,” says Gans. “Get ahead of the game and have that water bottle with you as a trigger to keep drinking.”

The key is to make drinking water part of your daily habits, considering it more of a lifestyle shift or pre-meal ritual than an atonement for last weekend’s calorie-consuming cheat day. “I tell people to go to bed with a glass of water on the nightstand so you can get into the habit of drinking water as soon as you get up,” says Gans, who keeps a sticky note on her computer screen to remind her to drink up during the day.

If you’re not big on the taste of plain old water (hey, no judgment), summer is the perfect season to flavor it. Add fresh berries or slices of cucumber, lime, watermelon or grapefruit to a pitcher, and keep it on hand in the fridge.

Gans also recommends using tonic water to make some fun summer mocktails that do double duty as a diet tool. Try mixing a 1/4 cup lemonade or orange juice (or any juice) with 3/4 cup tonic water for a healthy, refreshing drink.

You can also get water from some of your food sources as well. Loading up on watermelon slices at the next family cookout will help you lay off the dessert table and prevent the extra pounds.

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