Does drinking water help with weight loss?

Not much on its own. A 2024 review of 8 randomized trials in people with overweight pooled seven of them and found water programs lowered body weight by 0.73 lb (0.33 kg) on average, with a confidence interval running from 3.9 lb (1.75 kg) lost to 2.4 lb (1.08 kg) gained, and the authors rated that evidence low. The signal that does exist is narrower. In two small trials, adults on a calorie-cut diet who drank 17 fl oz (500 ml) of water before meals lost about 2.9 to 4.4 lb (1.3 to 2 kg) more over 12 weeks.

Unsettled. Water before meals is the one version of this advice with trial support, and it is thin. The two trials had 48 and 84 people, both lasted 12 weeks, and in the larger one the gap stopped being statistically significant once the analysis was adjusted. Nobody has pooled the premeal trials into a single estimate.

What the trials found

The best synthesis is a 2024 meta-analysis of randomized trials in adults and one group of adolescents with overweight, lasting 3 to 6 months. Some trials told people to drink more water and some told them to swap other drinks for it. Pooled, weight was 0.73 lb (0.33 kg) lower, the trials disagreed with each other a great deal, and the result did not reach significance.

The swap matters more than the water. In that same review, three trials of water replacing sugary drinks gave 1.8 lb (0.81 kg) more weight loss, with an interval that just touches zero. Two trials of water replacing diet drinks went the other way: people lost 4 lb (1.82 kg) less on water. A 2022 network meta-analysis of 17 trials in 1733 adults with overweight found the same shape, at low certainty and with some industry funding. Water instead of sugary drinks changed weight by 0.02 lb (0.01 kg). Diet drinks instead of water gave 2.4 lb (1.07 kg) more loss. Short single-meal studies help explain the sugary-drink result: adults ate 7.8% more total energy at a meal when they drank a sugary drink before it rather than water, in a literature the reviewers called sparse.

The premeal trials are where the hope comes from. A 2024 systematic review of 18 water trials found three in which adults with overweight drinking about 1.6 quarts (1.5 liters) a day before meals lost 44% to 100% more weight than controls, over 12 weeks to 12 months, without pooling them. In kilograms, the two trials with published numbers are small. In 48 adults aged 55 to 75 on a calorie-cut diet, 17 fl oz (500 ml) before each meal gave about 4.4 lb (2 kg) more weight loss over 12 weeks. In 84 adults with obesity in UK general practice, 17 fl oz (500 ml) half an hour before main meals gave 2.9 lb (1.3 kg) more at 12 weeks (95% CI 0.1 to 2.4), and the adjusted figure of 2.6 lb (1.2 kg) was not significant.

The larger and longer trial is less encouraging. In the CHOICE trial, 318 adults with overweight replaced caloric drinks with water for 6 months and lost 2.03% of their weight. The group that switched to diet drinks lost 2.5% and an attention control group lost 1.76%, and the differences between the three were not significant. A smaller exploratory trial in 45 Japanese adults found 500 g a day of carbonated water gave 1.6 lb (0.72 kg) more loss over 12 weeks than plain water, with many outcomes tested and no correction for that, as the authors say themselves.

An older 2013 review of 11 studies, mixing trials with observational data, reached the same place. Extra water lowered weight after 3 to 12 months in people already on a weight-loss program, and showed no effect in two short trials in people who were not dieting. The authors rated that evidence low.

Myth. Water does not burn calories in any way that matters. A 2003 report that drinking water raised energy use by 30% was tested again in a randomized crossover study, and about 17 fl oz (500 ml) of room-temperature water did not raise energy expenditure at all. Water chilled to 3 C raised it by 4.5% over an hour, which is a small physiology finding and not a weight-loss method.

Children and teenagers

In a randomized trial of 38 teenagers with overweight on a weight-loss diet in Boston, advice to drink 8 cups of water a day did not change BMI z score over 6 months. Few of them reached 8 cups, and water intake rose by only 1.6 cups a day more than in the control group. A review of 13 observational studies in children found 3 of 4 longitudinal studies linked more water with less overweight, while most cross-sectional studies linked it with higher weight. There were no randomized trials in that review and the authors called the evidence for cause low.

Who should be careful

The US National Academies set an adequate intake of about 2.9 quarts (2.7 liters) a day for women and 3.7 for men, counting food and all drinks, and set no upper level. No upper level does not mean that any amount is safe. The adequate intake is a guard against dehydration, and it was not built as a target for weight loss.

Not for everyone. Some people are told to drink less, and for them the advice to drink more does not apply as written. We have cards for two such groups. The European Society of Cardiology heart failure association considers fluid restriction of 1.6 to 2.1 quarts (1.5 to 2 liters) a day in selected patients with heart failure, as expert consensus. The American Gastroenterological Association advises 1.1 to 1.6 quarts (1 to 1.5 liters) a day for people with cirrhosis who have low blood sodium and fluid overload. If either applies to you, your fluid target comes from the team treating you.

Low blood sodium is the other risk named in sports guidance. A 2009 position stand for athletes says to drink enough to balance fluid losses and names low blood sodium in the same breath as dehydration. It gives no amounts. We looked for the consensus on low blood sodium during exercise and could not get its text, so there is no card for it here.

What expert bodies say

None of the bodies we found recommends water as a weight-loss treatment. The National Academies and the European Food Safety Authority set adequate intakes, and EFSA's two values are 2.1 and 2.6 quarts (2.0 and 2.5 liters) a day. The heart failure and liver bodies restrict fluid in their patients. The sports position stand frames drinking as replacing what is lost.

How we searched

What would change this answer

• A large adult trial of water before meals, longer than 12 weeks, reporting kilograms with an interval. None is registered.
• A meta-analysis that pools the premeal trials on their own. It does not exist, so the 44% to 100% figures stay as separate small trials.
• Results of the H2GO! cluster trial in 824 children, which is active and not recruiting.

More on water itself, including what it does for kidney stones: Water.

Sources

1. ev-wawl-01 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs with GRADE · n = 7 trials pooled for body weight
   In a meta-analysis of seven trials [16,17,18,19,20,21,22], the summary WMD in body weight comparing the water intervention group vs. the control group was −0.33 kg (95% CI = −1.75–1.08, p = 0.64) with high heterogeneity (I2 = 78%) (Figure 2A).
   
   Who: overweight and obese adults (7 trials) and adolescents (1 trial); 3 to 6 months; adding water or replacing other drinks with water
   Effect: body weight WMD -0.73 lb (95% CI -3.9 to 2.4; metric: -0.33 kg, -1.75 to 1.08), I2 78%; GRADE low for body weight
   Certainty: Only 8 trials, high heterogeneity; mixes adding water with swapping drinks.
   Nutrients, 2024, Water Intake and Adiposity Outcomes among Overweight and Obese Individuals: A Systematic Review and Meta-Analysis of Randomized Controlled Trials · checked 2026-10-06 · we read the fulltext
2. ev-wawl-02 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs, subgroup analysis · n = 5 trials
   Whereas substituting water for artificially sweetened beverages was positively associated with body weight (WMD = 1.82 kg, 95% CI = 0.97–2.67, I2 = 0%), substituting water for sugar-sweetened beverages was not (WMD = −0.81 kg, 95% CI = −1.66–0.03, I2 = 2%).
   
   Who: overweight and obese adults in substitution trials (3 replacing sugar-sweetened, 2 replacing artificially sweetened beverages)
   Effect: water for sugar-sweetened beverages WMD -1.8 lb (95% CI -3.7 to 0.07; metric: -0.81 kg, -1.66 to 0.03); water for artificially sweetened beverages WMD +4 lb (2.1 to 5.9; metric: 1.82 kg, 0.97 to 2.67)
   Certainty: Subgroups of 2 and 3 trials; the sugary-drink benefit has a CI touching zero.
   Nutrients, 2024, Water Intake and Adiposity Outcomes among Overweight and Obese Individuals: A Systematic Review and Meta-Analysis of Randomized Controlled Trials · checked 2026-10-06 · we read the fulltext
3. ev-wawl-03 · Meta-analysis or systematic review · systematic review of RCTs without pooling, Cochrane risk of bias · n = 4 trials on weight
   In 3 parallel group RCTs,18,19,20 adults with overweight and obesity randomized to consume 1500 mL of water per day before meals for a period of 12 weeks to 12 months had greater weight loss compared with those in the control groups (approximately 100%, 87%, and 44% more weight vs control groups).
   
   Who: adults with overweight and obesity randomized to 51 fl oz (1500 mL) water per day before meals for 12 weeks to 12 months; one adolescent trial
   Effect: approximately 100%, 87% and 44% more weight lost vs control in 3 adult trials; no effect in the adolescent trial (BMI z 0.0, 95% CI -0.1 to 0.1)
   Certainty: Narrative synthesis; small trials; relative figures, not kg.
   JAMA Network Open, 2024, Outcomes in Randomized Clinical Trials Testing Changes in Daily Water Intake: A Systematic Review · checked 2026-10-06 · we read the fulltext
4. ev-wawl-04 · Meta-analysis or systematic review · systematic review and network meta-analysis of RCTs with GRADE · n = 1,733
   Neither the primary outcome of body weight (MD, −0.01 kg; 95% CI, −0.95 to 0.98 kg) nor any of the secondary outcomes showed significant differences, although the direction of association favored water for most of the outcomes.
   
   Who: 1733 adults with overweight or obesity at risk for or with diabetes; water for SSBs in 3 trials (n 429), LNCSBs for water in 9 trials (n 974)
   Effect: water for SSBs body weight MD -0.02 lb (95% CI -2.1 to 2.2; metric: -0.01 kg, -0.95 to 0.98); LNCSBs vs water MD -2.4 lb (-4.3 to -0.42; metric: -1.07 kg, -1.95 to -0.19); certainty low for both
   Certainty: Low GRADE certainty for the water comparisons; median follow-up 12 weeks; some industry funding.
   JAMA Network Open, 2022, Association of Low- and No-Calorie Sweetened Beverages as a Replacement for Sugar-Sweetened Beverages With Body Weight and Cardiometabolic Risk · checked 2026-10-06 · we read the fulltext
5. ev-wawl-05 · Randomized controlled trial(s) · randomized controlled trial · n = 48
   Weight loss was ~2 kg greater in the water group than in the nonwater group, and the water group (beta = -0.87, P < 0.001) showed a 44% greater decline in weight over the 12 weeks than the nonwater group (beta = -0.60, P < 0.001).
   
   Who: overweight/obese adults aged 55-75 years, BMI 25-40, hypocaloric diet with or without 17 fl oz (500 ml) water before each daily meal
   Effect: ~4.4 lb (2 kg) greater weight loss over 12 weeks; 44% greater decline in weight (beta -0.87 vs -0.60)
   Certainty: Small, older adults only, diet given to both groups; meal intake effect faded by week 12.
   Obesity (Silver Spring), 2010 · checked 2026-10-06 · we read the abstract
6. ev-wawl-06 · Randomized controlled trial(s) · randomized controlled trial · n = 84
   The water preloading group lost -1.3 kg (95% CI -2.4 to -0.1, P = 0.028) more than comparators at follow up.
   
   Who: eighty-four adults with obesity from general practices in Birmingham, England; comparator imagined a full stomach before meals
   Effect: -2.9 lb (95% CI -5.3 to -0.22; metric: -1.3 kg, -2.4 to -0.1) vs comparator; adjusted -2.6 lb (-5.3 to 0.15; metric: -1.2 kg, -2.4 to 0.07)
   Certainty: Adjusted estimate not significant; 12 weeks only.
   Obesity (Silver Spring), 2015, Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity: RCT · checked 2026-10-06 · we read the abstract
7. ev-wawl-07 · Randomized controlled trial(s) · randomized controlled trial · n = 318
   Mean ((±SEM) weight losses at 6 mo were -2.5 ± 0.45% in the DB group, -2.03 ± 0.40% in the water group, and -1.76 ± 0.35% in the AC group; there were no significant differences between groups [corrected].
   
   Who: overweight and obese adults, BMI 36.3, 84% female, 54% black, replacing at least 200 calories/d of caloric beverages
   Effect: weight change at 6 mo: -2.03% water, -2.5% diet beverages, -1.76% attention control; no significant differences between groups
   Certainty: Control group also changed diet; differences between arms not significant.
   Am J Clin Nutr, 2012 · checked 2026-10-06 · we read the abstract
8. ev-wawl-08 · Randomized controlled trial(s) · randomized controlled trial · n = 38
   Advice and behavioral supports to consume 8 cups of water per day in the context of a weight-reducing diet did not affect body weight among adolescents with overweight or obesity.
   
   Who: adolescents with overweight or obesity drinking 4 cups or less of water per day, Boston, mean age 14.9 years
   Effect: difference in BMI z score change between groups -0.0 (95% CI -0.1 to 0.1), P = .88; water intake rose only 1.6 cups/d more than control
   Certainty: Few reached 8 cups a day; small trial.
   JAMA Pediatr, 2017 · checked 2026-10-06 · we read the abstract
9. ev-wawl-09 · Randomized controlled trial(s) · randomized crossover trial · n = —
   Energy expenditure did not increase after drinking either distilled water (P = 0.34) or 0.9% saline (P = 0.33).
   
   Who: healthy young volunteers drinking 7.5 ml/kg (about 18 fl oz (518 ml)) of distilled water, saline or 7% sucrose on different days
   Effect: no rise in energy expenditure after water (P = 0.34); water cooled to 3 C raised it by 4.5% over 60 min
   Certainty: Small physiology study; replies to a 2003 report of a 30% rise that did not replicate.
   J Clin Endocrinol Metab, 2006, Water-induced thermogenesis reconsidered: the effects of osmolality and water temperature on energy expenditure after drinking · checked 2026-10-06 · we read the abstract
10. ev-wawl-10 · Observational data · systematic review of randomized, non-randomized and observational studies · n = 11 studies
    In participants dieting for weight loss or maintenance, a randomized controlled trial, a nonrandomized controlled trial, and an observational longitudinal study showed that increased water consumption, in addition to a program for weight loss or maintenance, reduced body weight after 3-12 mo compared with such a program alone.
    
    Who: adults of any weight status; 11 original studies and 2 systematic reviews
    Effect: weight reduction after 3-12 months only when added to a weight-loss program; no effect in 2 short trials in non-dieters
    Certainty: Authors rate the evidence as low; mixes trials and cross-sectional studies.
    Am J Clin Nutr, 2013, Association between water consumption and body weight outcomes: a systematic review · checked 2026-10-06 · we read the abstract
11. ev-wawl-11 · Observational data · systematic review of observational and non-randomized studies · n = 13 studies
    On the cross-sectional level, higher water consumption seems to be associated with higher weight status.
    
    Who: children and adolescents aged 2-19 years; 4 longitudinal and 9 cross-sectional studies
    Effect: 3 of 4 longitudinal studies showed reduced overweight risk or BMI with more water; 6 of 10 cross-sectional analyses showed a direct association
    Certainty: No RCTs; authors call evidence for a causal link low.
    Obesity (Silver Spring), 2014, Association between water consumption and body weight outcomes in children and adolescents: a systematic review · checked 2026-10-06 · we read the abstract
12. ev-wawl-12 · Observational data · systematic review of clinical trials, epidemiologic and intervention studies · n = —
    In these comparisons, total energy intakes were 7.8% higher (DeltaTEI range, -7.5 to 18.9) when SSBs were consumed.
    
    Who: adults in single-meal clinical trials comparing beverages with water
    Effect: total energy intake +7.8% (range -7.5 to 18.9) with SSBs vs water; non-nutritive sweeteners vs water -1.3% (range -9 to 13.8)
    Certainty: Single-meal studies, no weight outcome; authors call the literature sparse.
    Nutr Rev, 2010 · checked 2026-10-06 · we read the abstract
13. ev-wawl-13 · Observational data · scoping review summarizing agency reference values · n = —
    Instead NASEM has made general recommendations for adequate intake (AI, cut-off values to prevent deleterious, primarily acute effects of dehydration and to ensure optimal body functions in relation to hydration status) of approximately 2.7 and 3.7 L from all beverages and foods daily for women and men (aged 19 to 30 years), respectively, but has not set an upper level for total water intake.
    
    Who: adults aged 19 to 30 years; total water from beverages and foods
    Effect: AI about 2.7 L/d women, 3.7 L/d men; no tolerable upper level; EFSA AI 2.0 and 2.5 L/d
    Certainty: Restates NASEM and EFSA positions for the Nordic Nutrition Recommendations 2023.
    Food Nutr Res, 2023 · checked 2026-10-06 · we read the fulltext
14. ev-wawl-14 · Position of an expert body · clinical consensus statement · n = —
    Consequently, the European Society of Cardiology HF guidelines have gradually downgraded these recommendations over time, now advising for the limitation of salt intake to no more than 5 g/day in patients with HF, while contemplating fluid restriction of 1.5-2 L/day only in selected patients.
    
    Who: patients with acute and chronic heart failure
    Effect: fluid restriction 1.5-2 L/day in selected patients; salt no more than 5 g/day
    Certainty: Expert consensus; people with heart failure should not follow 'drink more water' advice without their care team.
    Eur J Heart Fail, 2024 · checked 2026-10-06 · we read the abstract
15. ev-wawl-15 · Position of an expert body · clinical practice update, expert review · n = —
    Outpatient management of asymptomatic hypervolemic hyponatremia in liver cirrhosis entails both sodium and water restriction (aiming for 1-1.5 L of daily fluid intake), modification of diuretics and laxatives, and monitoring of electrolytes.
    
    Who: outpatients with liver cirrhosis and asymptomatic hypervolemic hyponatremia
    Effect: water restriction aiming for 1.1-1.6 quarts (1-1.5 L) of daily fluid intake
    Certainty: Expert best practice advice.
    Gastroenterology, 2025 · checked 2026-10-06 · we read the abstract
16. ev-wawl-16 · Randomized controlled trial(s) · randomized open-label parallel-group trial · n = 45
    At week 12, modest decreases were observed in body weight and body mass index (BMI) compared with placebo (body weight: -0.72 kg; 95% CI - 1.37 to - 0.07; P = 0.036; BMI: -0.26 kg/m²; 95% CI - 0.50 to - 0.02; P = 0.037).
    
    Who: healthy Japanese adults aged 20-64 years, BMI 23.0 to under 30.0; carbonated vs non-carbonated water once daily
    Effect: body weight -1.6 lb (95% CI -3 to -0.15; metric: -0.72 kg, -1.37 to -0.07) vs plain water at week 12; snacking -1.49 times/week
    Certainty: Exploratory, multiple outcomes without multiplicity adjustment (authors' own caveat).
    Sci Rep, 2026 · checked 2026-10-06 · we read the abstract
17. wat-dr-07 · Position of an expert body · joint position stand of the American Dietetic Association, Dietitians of Canada and the American College of Sports Medicine, based on a systematic evidence-based analysis of the nutrition and performance literature · n = —
    Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses.
    
    Who: athletes and physically active people
    Effect: the position says athletes should be well hydrated before exercise and drink enough during and after to balance fluid losses, and that sports beverages with carbohydrate and electrolytes may decrease the risk of both dehydration and hyponatremia
    Certainty: a position stand is an organization's reading of the literature, not data, and this one dates from 2009. It carries no amounts and no threshold, so it cannot answer how much anyone should drink. Full text not retrievable (no_pmc)
    Med Sci Sports Exerc, 2009 · checked 2026-09-22 · we read the abstract