Just about any weight loss coach/program I've ever seen say that drinking a lot of water (exact amount vary) combined with a low-calorie diet helps with losing weight (compered to the diet alone)

Does drinking more water have any effect on weight loss?

Here are some sources of this claim on the web (found via search, I'm asking because I've heard the claim off-line) - including the well-respected source for medical information CNN :-) - 1 2 3 4

Notice that every source gives different reasons why drinking lots of water is so important - a sure sign of reliable scientific fact

2 Answers 2


There's some evidence that drinking a large amount before eating a meal will help because it makes you feel more full, thus leading to eating less food, but sipping it during your meal doesn't help much because the water is absorbed much faster than the food.

People sometimes drink water with meals to promote a feeling of fullness, in hopes of helping limit how much they eat. Kuo says that this probably doesn't work if you just sip water with a meal, because liquid passes through the stomach much more quickly than food and so doesn’t have time to stretch the stomach and provide that feeling of fullness.

Your best chance for that effect is to drink a lot of water just before a meal, and then eat fairly quickly.

A small recent study by researchers at Virginia Tech supports this idea, finding that dieters who drank two eight-ounce glasses of water before meals lost more weight than those who didn’t.


“We are presenting results of the first randomized controlled intervention trial demonstrating that increased water consumption is an effective weight loss strategy,” said Brenda Davy, Ph.D., senior author on the study. “We found in earlier studies that middle aged and older people who drank two cups of water right before eating a meal ate between 75 and 90 fewer calories during that meal. In this recent study, we found that over the course of 12 weeks, dieters who drank water before meals, three times per day, lost about 5 pounds more than dieters who did not increase their water intake.”


The study included 48 adults aged 55-75 years, divided into two groups. One group drank 2 cups of water prior to their meals and the other did not. All of the subjects ate a low-calorie diet during the study. Over the course of 12 weeks, water drinkers lost about 15.5 pounds, while the non-water drinkers lost about 11 pounds.

Thermogenesis, the idea that you burn calories by drinking cold water because your body has to work to heat it up, currently is discredited due to the evidence showing that it accounts for a few calories at most if you constantly drink ice water.

Lastly, there is some small benefit found in substituting water for other beverages simply because water has no calories, so drinking a glass of water instead of a glass of juice or cola is a net difference in calories.

  • Can you please provide references to two other claims you made ".. currently is discredited due to the evidence showing that it accounts for a few calories at most if you constantly drink ice water." and "drinking a glass of water instead of a glass of juice or cola is a net difference in calories." Thanks.
    Sep 23, 2014 at 22:01
  • 4
    @DMINATOR: That second claim seems more like basic arithmetic than a claim, providing you accept that water has no calories and juice or cola has calories.
    – jl6
    Sep 24, 2014 at 6:58


Good analysis by Sean Duggan. I would like to take a look at Thermogenesis a bit closer.

Let's start with Metabolism

Metabolism refers to biochemical processes that occur with any living organism - including humans - to maintain life. These biochemical processes allow us to grow, reproduce, repair damage, and respond to our environment.

Anabolism and catabolism

Anabolism is the building up of things - a succession of chemical reactions that constructs or synthesizes molecules from smaller components, usually requiring energy in the process.

Catabolism is the breaking down of things - a series of degradative chemical reactions that break down complex molecules into smaller units, and in most cases releasing energy in the process.

Metabolism and body weight

In simple terms, our body weight is a result of catabolism minus anabolism. In other words, the amount of energy we release into our bodies (catabolism) minus the amount of energy our bodies use up (anabolism).

The excess energy is stored either as fat or glycogen (stored as carbohydrate mostly in the liver, and also in the muscles).

One gram of fat produces 9 calories (kcal), compared to 4 kcal from protein or carbohydrate.

What is metabolism? How do anabolism and catabolism affect body weight?


The basal metabolic rate (BMR) represents the energy needed to support the basic cost of living. The BMR is typically measured in the morning after an overnight fast and lying down for 30 minutes

RMR (Resting Metabolic Rate) is any time of day

The largest number of calories expended by most people (except for athletes during heavy training) is from the resting metabolic rate (RMR)

Your Metabolism: Facts and Fables

According to this study (refers to changes in RMR levels):

The novel finding in this study is that drinking 500 ml of water increases metabolic rate by 30% in both men and in women. The increase in metabolic rate was observed within 10 min after completion and reached a maximum 30–40 min after water drinking. The effect was sustained for more than an hour.

Based on our measurements, we estimate that increasing water ingestion by 1.5 liters would augment daily energy expenditure by approximately 200 kJ. Over 1 yr, energy expenditure would increase by 73,000 kJ (17,400 kcal), the energy content of 2.4 kg adipose tissue.

adipose tissue = fat

Water-Induced Thermogenesis

My conclusion as far as I understood this topic: Drinking water does increase metabolic rate for a short period of time, contributing to the additional energy expenditure of the human body (ie burning calories).

  • The conclusion is too strong, given the evidence you present. While you show it does have an effect, the quantification of it is very theoretical. Can we expect people to drink 1.5 liters of extra water every day for a year in order to lose 2.4kg? With most diets, the problem is that the body adapts: one eats less calories, the body lowers the BMR to compensate, etc.
    – Sklivvz
    Sep 24, 2014 at 9:16
  • @Skliwz Yes you are right, but the question was very specific "Does drinking more water have any effect on weight loss". There is an effect on weight loss, anything beyond that (how effective it actually is compared to other methods) is a different question that will be a bit more difficult to answer.
    Sep 24, 2014 at 16:13
  • The thermogenesis argument is that if you drink ice water your body has to heat it up, and the amount of calories that requires is what your body has to burn to get the temperature up. The misconception arises when people do a basic calculation (e.g energy to raise 500mL of water by 15 degrees), get a certain number of calories, (500 x 15 = 7500 small calories) and think "wow, that is heaps", forgetting that "calories" in food is actually kilocalories (7.5 calories = 31.4kJ for the example) and pretty much insignificant. Jan 8, 2015 at 22:14
  • That the actual amount of energy burnt by the body to do this is a bit more (100kJ instead of 31kJ) and that it comes from fat, is interesting. I wonder if instead of saunas, people start sitting in cold rooms to lose weight :P Jan 8, 2015 at 22:18

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