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Drinking Water can help you Lose Weight

The science behind water intake and weight loss

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First published: 11.Oct.2018

Does water promote weight loss?

Several studies have shown that there is a positive correlation between drinking more water than one usually drinks, and weight loss.

In other words: drink more water, and you will very likely lose weight.

The biochemical reason for this weight loss is not yet clearly understood. Furthermore, some studies have reported no weight loss at all.

In this article, we will look into the scientific evidence and discuss some of the possible mechanisms that cause weight loss when hydration is increased.

Drinking water may help you get slim

Drink Water before your main meals to Lose Weight

Parretti's Study

In 2015, a team led by Dr. Helen Parretti (1) studied a group of 84 obese adults. They gave them advice on how to improve their diet and increase physical activity.

The subjects were split into two groups: one of them had to drink 500 ml (half a quart or 17 fl. oz) of water half an hour before eating their main meals; the other group (control) had to imagine that they had a full stomach before eating.

Study's Outcome

  • After 12 weeks those who drank water before their meals lost an extra 2.87 lb (1.3 kg) compared to the control group.
  • Those who drank water before all three main meals lost 9.48 lb (4.3 kg) while those who only had water before one main meal, or not at all, only lost 1.76 lb (0.8 kg).

Meaning that if you are an overweight adult and drink one-half quart of water before each of your main meals, you could shed some body weight.

A Contradicting Study

In a more limited study, (McKay 2018) (2) studied 49 participants who consumed either one, two, or three 500 ml bottles of water during the morning and then measured their caloric intake and hunger at lunchtime.

They found that only "normal" weight subjects ate less at lunch (with a lower caloric intake); obese or overweight participants were not affected by drinking water before their meal and ate the same quantity as usual.

Perhaps the limited scope (in duration and intensity - they only drank water before one meal) of this study is the reason for its outcome that disputes Parretti's findings.

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Increased Hydration works for those who are Dieting

Muckelbauer (2013) (3) conducted a systematic review of scholarly articles about the link between water consumption and weight loss; the team concluded that "Studies of individuals dieting for weight loss or maintenance suggest a weight-reducing effect of increased water consumption".

In other words, drinking water if you are dieting does help you lose weight.

But they added that mixed-weight populations that were not focused on weigh-loss "showed no effect of water consumption on body weight [or] showed inconsistent results" (such as the effect noticed by McKay), they believed that this was due to the lack of good-quality studies.

Drinking water for weight loss works well with Older Adults

The following studies reported that increasing water consumption helped middle-aged and older adults lose weight.

The weight loss was less in young adults.

In the first study (Dennis, 2012) (4) obese adults aged between 55 and 75 years with a Body Mass Index of 25 to 40, were divided into two groups, one drinking half a quart (500 ml) of water before each meal and the other drinking none.

Both groups also followed a low-calorie diet for 12 weeks.

The study found that:

  • Those drinking water before their main meals lost an additional 4.4 lbs. (2 kg) compared to the "non-water group".
  • The "water" group also had a 44% greater weight loss than the non-water group.

Another study (Davy, 2008) (5) gave "older" obese subjects (mean age of 61.3 years) a 500 ml (half a quart) premeal drink of water. It found a "13% reduction in meal energy intake" which "was not related to sex, age, body mass index, or habitual daily water consumption".

In other words, they ate less, and this was due to having consumed water before their meal.

Energy Intake

Energy Intake (EI) is how many calories are consumed during a meal.

A third study (Walleghen, 2007) (6) compared the energy intake during meals of healthy non-obese subjects which were grouped into young (age: 21 - 35 years) and older (age: 60 - 80 years) cohorts. Each group was further subdivided into sub-groups that were either given water or not.

Walleghen and her team found that:

  • Young subjects ate the same amount of calories whether they had or hadn't drunk water.
  • Older subjects who had drunk water ate fewer calories (8.5% less) than those who hadn't.
  • Hunger (satiety) and fullness were higher in older subjects.
  • All those who had drunk water (older and younger) had better fullness ratings than those who hadn't drunk water.

Their Conclusions: "pre-meal water consumption reduces meal energy intake in older but not younger adults."

Why does drinking water cause Weight Loss?

Which are the mechanisms that cause you to lose weight by increasing water consumption?

Below we will look into three possible ways that drinking more water impacts your metabolism leading to weight loss:

woman drinking a glass of water
Drink your daily water requirements. Aqua Mechanical

1. Water is a Zero Calorie liquid

Water itself is a zero-calorie drink, so for some people, replacing soft drinks, sweetened beverages such as coffee or tea, or fruit juices with water is a calorie lowering alternative.

Calories in Food

The international unit for energy in food is the kilojoule or kJ. However, the most commonly used unit is what everyone calls calorie (abbreviated Cal).

One Cal is equivalent to 1000 "small" calories, or in other words, one Cal is equal to one kilocalorie (kcal).

Just as an example, a 12 fl oz can (355 ml) of regular Coca-Cola has 140 Cal, all of them from sugar! (1.4 oz. - 39 g of sugar in the can).

A sports drink like a Lemon Lime Gatorade also has 140 Cal (20 fl oz - 591 ml) all of them carbohydrates including 1.3 oz. - 36g of sugar.

Alcoholic beverages are also loaded with calories (a 12 fl oz Budweiser packs 145 Cal).

Switching from sugar or high-fructose laden drink to plain water can contribute to a lower energy intake and, potentially, to lower body weight.

Tate (2012) (7) explored this option by studying a group of obese and overweight adult men and women with an average BMI of 36.3.

What is BMI?

Body Mass Index or BMI is a relationship between a person's height and weight. Although it does not measure your body fat directly, it provides a good estimate of a person's weight type (obese, overweight, normal, or underweight).

It is widely used because it is an easy and inexpensive way to define a person's body fat.

Read More, visit our > > BMI Calculator

Tate's subjects substituted caloric beverages with non-caloric ones: either water (Water Group) or diet beverages (DB).

A control group (AC) was not instructed on what beverages to drink. All participants were given information on how to modify their diets to lose weight. The trial lasted six months, and the study found that:

  • All three groups lost some weight, but very little: on average it was approximately a drop of 2%.
  • The "Water Group" lost 2.03% of their weight, the "DB" group lost 2.5%, while the "AC" control group lost the least weight: 1.76%.
  • The fasting glucose (blood sugar) improved in the "water" group. The "DB" group improved too but was similar to the "AC" control group.
  • Those who were assigned to the beverage replacement groups ("water" and "DB") were 2 times as likely to have achieved a 5% weight loss than were the "AC" participants.

The authors concluded that: "replacement of caloric beverages with noncaloric beverages as a weight-loss strategy [...] could have public health significance and is a simple, straightforward message."

Should you drink Water or Diet Beverages?

Tate's study showed that water or a diet beverage is less fattening than a sweetened drink. But, which one is better?

A study (Madjd, 2015) (8) addressed this issue. It involved overweight and obese women with a BMI of 27 to 40, aged 18 to 50, who usually drank Diet Beverages (DB). The authors split them into two groups during a 24-week weight loss program:

One group replaced their DB with water ("water" group), while the other continued drinking DB. The results were the following:

  • The "water" group lost 15.7% more weight than the DB group (average of 19.5 lb - 8.8 kg vs. 16.8 lb - 7.6 kg).
  • "Water" group's fasting insulin also improved more than that of the DB subjects.
  • The fasting glucose and waist circumference were similar in both groups.

The authors reported that "Replacement of DBs with water after the main meal may lead to greater weight reduction during a weight-loss program [and] may also offer clinical benefits to improve insulin resistance."

Another study (An, 2013) (9) reviewed data involving almost 125,000 men and women over four years and found that:

  • All of the participants gained an average of 3.2 lb (1.45 kg) during the study. Which confirms the current global "fattening" trend.
  • However "increasing plain water and coffee intake was inversely associated with weight gain" meaning that those who drank more water and coffee gained less weight than the other subjects.

An's team concluded that "substitution of sugar-sweetened beverages or fruit juices by non-caloric beverages, like plain water, is related to less weight gain".

The table below summarizes their findings. Adding an extra cup of one of these drinks reduces weight gain by:

Adding one extra
cup per day of

Reduction in weight gain


-0.29 lb (-0.13 kg)


-0.31 lb (-0.14 kg)


-0.07 lb (-0.03 kg)

Diet Beverages

-0.22 lb (-0.10 kg)

Replacing one serving per day of a sugar-sweetened beverage for a cup of water led to 1.1 lb less weight gain (0.49 kg) during the four years compared to those who kept on drinking sweetened drinks.

If one serving of fruit juice was replaced by water the subjects experimented 0.77 lb (0.35 kg) less weight gain than those who made no changes.

The message is clear: replace sugar-sweetened beverages with unsweetened ones such as water, tea, coffee, or diet beverages, and you may not lose weight, but you will gain less weight than if you stuck to your "bad" habits.

Coffee or Water?

Killer (2014) (10) compared the effects of drinking coffee or water on hydration.

They debunked the idea that drinking coffee should be avoided to maintain a fluid balance: Killer studied 50 young men who drank either 800 ml (4 cups) of coffee or water and found that "There were no significant changes in TBW (Total Body Water) from beginning to end of either trial."

The coffee drinkers lost a bit more sodium through their urine.

The other finding was a small yet progressive daily weight fall in both Coffee and Water groups of almost one pound (0.4 kg).

Read More at our:

> > Do coffee or tea hydrate as water does? webpage
Yes, they do, and they count against your daily water requirements.

2. Water makes you burn more calories

Another plausible mechanism is that an increased water intake drives "thermogenesis" (you burn more energy to "digest" the water) which in turn leads to weight loss:


Thermogenesis or the "Thermogenic Effect" of food is the energy required for digesting and absorbing food, and the stimulating influence that food has on the body. The word combines the Greek words "Thermos" (heat, warmth) and "Genesis" (origin).

Studies on additional energy expenditure

A study by Girona (2014) (11) had twelve subjects drink half a quart (500 ml) of cold and room-temperature water.

The researchers found that the subject's energy expenditure increased by 3% above their usual levels during the 90 minutes that followed drinking the water.

They concluded that the body consumed additional energy to heat the water to body temperature.

Another positive side effect was a reduction in the heart rate and therefore less workload for the heart.

From a physical point of view, heating one ounce (28 g) water from around 50°F (10°C) to body temperature (98.6°F - 37°C) requires an expenditure of only 0.8 Calories. That means that drinking one glass of cold water would only burn extra 5.4 Calories compared to drinking water at body temperature.

Boschmann, (2003) (12) studied the effect of water on thermogenesis and found that:

Drinking 500 ml of water increased the metabolic rate by 30% with a thermogenic response of around 24 Calories. Half of this was due to having to warm water from room temperature to body temperature. But why did the body burn even more energy than was needed to heat the water? They didn't explain this effect.

They concluded that this thermogenic effect "should be considered when estimating energy expenditure ... during weight loss programs".

However, another study (Brown, 2006) (13) failed to replicate this finding, detecting only a small 4.5% increase in energy expenditure under similar conditions.

But another study confirmed that water-induced thermogenesis helped overweight girls lose weight (Vinu, 2013) (14):

Vinu's subjects drank 500 ml of water before each of the three main meals during eight weeks, resulting in a bodyweight and BMI decrease of 2.2%.

3. Water suppresses appetite

This is based on the idea that once the stomach fills up with water, it signals the brain-stimulating a feeling of fullness and satiety.

This "appetite suppression" theory has been studied with mixed results:

Dennis (4) found that "Water consumption acutely reduces meal energy intake (EI) among middle-aged and older adults..." implying that fewer calories were eaten due to a feeling of satiety after drinking water.

McKay's study (2) didn't find a lower caloric intake in obese subjects (only "normal" weight participants ate less during lunch after having drunk water), yet they did detect that "water intake suppressed liking of food items in all participants and hunger in females."

Walleghen's study (6) suggests that hunger is suppressed in older adults due to their slower gastric emptying time which is around 34% (12 minutes) longer than that of younger adults. This may give time for the brain to recognize satiety and signal to stop eating.

Walleghen also found that "healthy older adults report less hunger and more fullness in response to a meal" than younger adults, suggesting that aging may explain the different sensations of hunger or fullness.

Water and Hormones interact

The stomach has stretch receptors in it that detect its change in size as it fills with food (or, in our case, water). These receptors send signals to the brain to indicate satiety.

Additionally, the first phase of digestion begins in the duodenum the first segment of the small intestine, and the cells located in the walls of the small intestine release "gut hormones" known as Cholecystokinin (CCK) which affect the brain reducing the feeling of hunger.

Kusano (2005) (15) looked into the effects of water on the gastrointestinal tract following a meal. They found that drinking 500 ml of water 1 hour after a standard 560 Kcal meal increased the level of CCK in the blood, reducing the sensation of hunger.

A recent study by Camps (2018) (16) explored the effect of "gastric distention" or stomach stretching after a meal and how it interacts with the brain.

They set up an MRI scan to measure both stomach content and blood flow in the brain after the subjects drank either a low volume (50 ml) or a high volume (350 ml) drink of water.

They found that those who drank the "high volume" of water had significantly increased fullness and decreased hunger than those who drank the "low volume" of water.

The increased water load activated a brain area called the mid-temporal gyrus which may have some yet unknown role in satiety.

Thornton (2016) (17, 18) proposed that hydration leads to bodyweight loss mainly through a reduction in feeding and a loss of fat due to increased lipolysis.

Thornton pointed out that "this increased water intake [...] produced a marked decrease in adiposity [...] unblock[ing] fat metabolizing mechanisms [...] the increased water intake per se allows cells to hydrate better and thus regulate fat metabolism better.

Lipolysis: Fat Metabolism

Lipolysis is a process that breaks down fats and turns them into glycerol and free fatty acids to provide energy to the body.

The increase in lipolysis after drinking water may be due to the increase in cell volume as the cells absorb the extra water. This in turn increases mitochondrial activity (the mitochondria produce the cell's energy and regulate cellular metabolism).

Heightened metabolism then increases lipolysis in the fatty tissue.

Another mechanism proposed by Thornton involves the kidneys: higher hydration causes the release of atrial natriuretic peptide (ANP) which activates a protein called uncoupling protein 1 (UCP1), which increases fat metabolism and a loss of body weight. ANP also increases sodium excretion by the kidneys.


There is considerable evidence supporting the notion that drinking unsweetened beverages (water, diet drinks, coffee, or tea) will help you lose weight.

In the meantime, you should check if you are well hydrated. Work out your fluid intake and compare it with the recommended guidelines of the National Academy of Medicine (NAM) for adults:

  • 91 ounces of total water for women (2.7 liters)
  • 125 ounces of total water for men (3.7 liters)

"Total water" means water from all the beverages and foods consumed each day. Estimate that 20% of your water comes from food (vegetables, beef, eggs, meat, fruits).

glasses of water with mint and berrries
Water can be a tasty drink too.

References and Further Reading

(1) Helen M. Parretti, Paul Aveyard, Andrew Blannin, Susan J. Clifford, Sarah J. Coleman, Andrea Roalfe, Amanda J. Daley. (2015). Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity. RCT. Obesity, 2015; DOI: 10.1002/oby.21167

(2) McKay Naomi J., Belous Ilona V., Temple Jennifer L. (2018). Increasing water intake influences hunger and food preference, but does not reliably suppress energy intake in adults. Physiology & Behavior Volume 194, 1 Oct. 2018, 15-22.

(3) Rebecca Muckelbauer, Giselle Sarganas, Anke Grüneis, Jacqueline Müller-Nordhorn. (2013). Association between water consumption and body weight outcomes: a systematic review. The American Journal of Clinical Nutrition, V 98: 2, 282-299,

(4) Elizabeth A. Dennis et al. (2012). Water Consumption Increases Weight Loss During a Hypocaloric Diet Intervention in Middle-aged and Older Adults.

(5) Davy BM, Dennis EA, Dengo AL, Wilson KL, Davy KP. (2008)Water consumption reduces energy intake at a breakfast meal in obese older adults. J Am Diet Assoc. 2008 Jul;108(7):1236-9. DOI: 10.1016/j.jada.2008.04.013.

(6) Emily L. Van Walleghen, Jeb S. Orr, Chris L. Gentile, Brenda M. Davy (2012). Pre-meal Water Consumption Reduces Meal Energy Intake in Older but Not Younger Subjects.

(7) Deborah F Tate et al. (2012). Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical tria. The American Journal of Clinical Nutrition, Volume 95, Issue 3, 1 March 2012, Pages 555-563,

(8) Ameneh Madjd et al. (2015). Effects on weight loss in adults of replacing diet beverages with water during a hypoenergetic diet: a randomized, 24-wk clinical trial The American Journal of Clinical Nutrition, Volume 102, Issue 6, 1 December 2015, Pages 1305-1312,

(9) An Pan et al. (2013). Changes in water and beverage intake and long-term weight changes: results from three prospective cohort studies, Int J Obes (Lond). 2013 Oct; 37(10): 1378-1385. 2013 Jan 15. DOI: 10.1038/ijo.2012.225

(10) Sophie C. Killer, Andrew K. Blannin, and Asker E. Jeukendrup (2014). No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population. PLoS One. 2014; 9(1): e84154. Published online 2014 Jan 9. DOI: 10.1371/journal.pone.0084154

(11) Girona M, Grasser EK, Dulloo AG, Montani JP. (2014). Cardiovascular and metabolic responses to tap water ingestion in young humans: does the water temperature matter? Acta Physiol (Oxf). 2014 Jun;211(2):358-70. DOI: 10.1111/apha.12290. Epub 2014 Apr 15

(12) Boschmann M, et al. (2003). Water-induced thermogenesis, J Clin Endocrinol Metab. 2003 Dec;88(12):6015-9. DOI: 10.1210/jc.2003-030780

(13) Brown CM, Dulloo AG, Montani JP. (2006) Water-induced thermogenesis reconsidered: the effects of osmolality and water temperature on energy expenditure after drinking. J Clin Endocrinol Metab. 2006 Sep;91(9):3598-602. Epub 2006 Jul 5.

(14) Vinu A. Vij and Anjali S. Joshi. (2013). Effect of ’Water Induced Thermogenesis’ on Body Weight, Body Mass Index and Body Composition of Overweight Subjects. J Clin Diagn Res. 2013 Sep; 7(9): 1894-1896. DOI: 10.7860/JCDR/2013/5862.3344

(15) Kusano M et al. (2005). Postprandial water intake inhibits gastric antral motility with increase of cholecystokinin in humans. Scand J Gastroenterol. 2005 Oct;40(10):1176-81

(16) J Camps G, Veit R, Mars M, de Graaf C, Smeets PA. (2018). Just add water: Effects of added gastric distention by water on gastric emptying and satiety related brain activity. Appetite. 2018 Aug 1;127:195-202. DOI: 10.1016/j.appet.2018.04.023. Epub 2018 May 3

(17) S N Thornton (2016). Increased Hydration Can Be Associated with Weight Loss. Front Nutr. 2016; 3: 18. Published online 2016 Jun 10. DOI: 10.3389/fnut.2016.00018

(18) S N Thornton, P C Even & G van Dijk. (2009). Hydration increases cell metabolism. Letter to the Editor, Nature 20.Jan.2009

About this Article

Increased water intake promotes weight loss, A. Whittall

©2018, 11 Oct. 2018. Updated. 27 Oct. 2020.

Tags: Dehydration, 8 x 8 rule, hydration, water requirements, daily water intake, weight loss, weight.

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Subject: Drinking more water can help you lose weight. Learn about the studies and science behind this surprising claim. Higher water intake promotes weight loss.

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