The Science Behind Why Water Is Good for Weight Loss

Macaela Mackenzie
by Macaela Mackenzie
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The Science Behind Why Water Is Good for Weight Loss

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.

About the Author

Macaela Mackenzie
Macaela Mackenzie

Macaela is a writer based in New York City with a passion for all things active. When she’s not writing about the weirdest fitness trends or nutrition news, you can find her conquering her fear of heights at the rock climbing gym, hitting the pavement in Central Park or trying to become a yogi. To see Macaela’s latest work, visit


18 responses to “The Science Behind Why Water Is Good for Weight Loss”

  1. Avatar Jeffrey Kirkwold says:

    This is science? Not even an attempt to track if excess water consumption leads to weight loss? Just because I feel fuller for a short time (absorption delay), does that always translate to less calories consumed or is that a hasty conclusion? Jeeze, the things that pass for science these days. I’d like to see a double blind study where water consumption is the only significant variable tracked over a substantial amount of time. Say 6-18 months. THAT would be science.

    • Avatar Jeffrey Sucks says:

      Shut it nerd

      • Avatar Drew says:

        I totally agree with the original commenter, but the “shut it nerd” made me laugh. Probably because I totally see my own nerdiness in wanting the same double blind study. You should see my OCD weight loss graphs…

      • Avatar davedave12 says:

        actually, this is an excellent diet plan “shut it”

    • Avatar davedave12 says:

      if you always drink very cold water and take cold baths you will shiver and burn calories — there are lots of good suggestions like this on “Ana” web sites

  2. Avatar Anne says:

    Don’t know why, but “Society for the Study of Ingestive Behavior” cracked me up! There ARE scientists who study Ingestive behavior…who knew?! So I clicked on the link and yup, the fMRI pics are there. No double blind, long term study, but a scientific study with data none the less. Now the author’s leap in taking this study and stating water intake leads to weight loss IS a stretch, since the study was not about that, but this is a blog not a journal, so I will take it as such.

  3. Avatar NGB says:

    Are you sure you mean tonic water and not soda water/carbonated water? Tonic water is pop and 33 g of sugar in a regular can, nearly the same as Coke.

    • Avatar Adrian says:

      This may be so, but first keep in mind that diet tonic water exists. Besides, with the “mocktail” described, it’s nice to have something like this from time to time… If you spent the other 364 days of the year being absolutely perfect, why not have something like this on one of those days?

      • Avatar NGB says:

        I completely agree that treats are fine on occasion and even necessary, we are all human! But in that case why promote tonic as it is no different than other sodas? I also know several people who thought vodka tonic was a “healthier” option for weekend drinks as tonic doesn’t taste particularly sweet but it still is high in sugar and the same as any coke or Sprite drink. I just think the text is misleading!

  4. Avatar Diana says:

    Why do I still feel thirsty after drinking my water? Its like I can’t get enough,.

    • Avatar Kris Swanson says:

      Usually means you are chronically dehydrated and didn’t know it. I just learned about this when I started my weight loss journey in March. I went from no water ever to 60-90 oz per day. Now I can’t go without it. And to you naysayers who say drinking lots of water doesn’t help with weight limit as, I’m here to tell you it worked great for me. Once my body was consistently hydrated I wasn’t as hungry and I have lost 35 lbs so far. No more soda. Water also flushes toxins out of your body which also increases weight loss bc your digestive system and your metabolism both work more efficiently when you are properly hydrated. I can tell a big difference any day that I don’t get at least 8 oz.

  5. Avatar Peter T says:

    An interesting read and this does make some sense.

    However in my opinion the best way to lose weight is to cut down or stop eating junk food such as fast-food and takeaways, cut down on high fat foods, and exercise more.

    If you’re feeling hungry, your body is telling you it needs energy to cope with the activity you’re doing.

    Ok common sense says you don’t eat whilst exercising. However you should have something to eat before and after a workout to keep your energy up and aid recovery, and drink plenty of water during exercise to replace water lost through sweat.

    You need to listen to your body as it’s very good at telling you what you need and don’t need. Whether that be water, food or a particular food.

    I’ve found I’ve craved certain foods at times such as strawberries or spinach. This is telling me my body needs an intake of iron. Other times it’s chicken…protein.

    The sight and smell of a McDonald’s makes me feel sick…my body’s way of telling me it hated that sort of food because it’s processed crap.

    Not all may agree with my thoughts here, but I believe your body is very good at telling you what it needs.

  6. Avatar Techno Spice says:

    The water push often translates poorly. The boyfriend drinks 2 gal of water a day and nags me endlessly that I don’t drink enough at my ~90 oz. But if I drink more I cramp like crazy when running or sleeping. He refuses to believe it’s the water. And ignores me when I try to explain cellular osmosis and electrolyte balances. Water is great, but only when your body is in homeostasis. You have to drink more electrolyte beverages if you start drinking more than regular hydration. A good sign if that is clear urine.

  7. Avatar Abid Kunda says:

    I think drinking water is good for your all round health and any relation to weight loss is at best oblique. But need to keep in mind that excess of water consumption may lead to loss of sodium which brings with it problems of its own.

  8. Avatar George Garrick says:

    I recently lost 30 pounds in 4 months which is a fairly gradual rate, and I only started at 204. I’d attribute a big part of that to drinking sparkling water constantly all day long. I always carry a bottle with me or have one at my desk. Because it’s carbonated, the gassiness makes you feel full. So feeling full means you are less likely to want to snack or to eat more than small portions at meals. And it gradually trained me to just not snack and to always eat small portions at sit down meals. I don’t miss the food a bit and it’s now become a new lifestyle habit. It works. But I recommend sparkling water. Crystal Geyser was my favorite because it’s a bit more heavily carbonated than Pellegrino.

    • Avatar iipostmvh says:

      I’ve done the same thing and I know it play a huge role in the almost 35 pounds I’ve lost since March. I used carbonated water to kick my soda habit…I haven’t had one or craved one since. Of course that’s automatically going to cause calorie loss. One word of caution/suggestion: still mix in plain ol water during the day. The carbonated water 100% isn’t good and can cause wear on your teeth. I hate plain water but adding fruit, pineapple, peaches and mint, lemon, etc helps.

  9. Avatar Robert Glazauskis says:

    It’s says in Gans also recommends tonic water water to make some fun summer mock tails. From reading label I find most tonic water on the markets contains some of the same aweful ingredients found in regular soda. Maybe I am wrong, but would that then not be a good choice. I tend to mix things with seltzer water after first reading the label on the can or bottle. If see bad things on the label. I avoid it!

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