Does a high-protein diet help with weight loss?

A little, and less as time goes on. Across 24 randomized trials in 1063 adults on equal-calorie weight loss diets of about 12 weeks, the higher-protein version took off 1.7 lb (0.79 kg) more weight (95% CI 0.08 to 1.50) and 1.9 lb (0.87 kg) more fat, a modest gain next to what the calorie deficit itself removed. Over 12 months or more the extra loss shrinks to about 0.88 lb (0.4 kg). The calories you cut still do almost all of the work.

Established. When calories are matched, a diet higher in protein takes off slightly more weight and fat and keeps slightly more lean mass. Three meta-analyses of randomized trials and a fourth of studies with a year or more of follow-up agree on the direction, and none of them finds a large effect.

What the trials found

The cleanest test holds calories and fat steady and swaps carbohydrate for protein. In those 24 trials the higher-protein diet also kept 0.95 lb (0.43 kg) more fat-free mass (0.09 to 0.78). Only 3 of the 5 studies that measured fullness reported more of it.

A larger pooling of 37 trials in adults with overweight or obesity, with protein at 18 to 59 percent of energy, found 3.5 lb (1.6 kg) more weight loss (1.2 to 2.0), though only some of those trials cut calories at all. A review of 74 trials reported the effect as a standardized difference of 0.36 for weight and 0.43 for waist size, which the authors call small to moderate and which cannot be turned back into kilograms.

Time is where the advantage leaks away. In 32 studies with 3492 people followed for at least a year, advice to eat more protein and fewer carbohydrates left about 0.88 lb (0.4 kg) of extra weight loss, an effect the authors call small, and these were mostly short intensive programs whose advice people followed less as months passed. The largest single trial, POUNDS Lost, put 811 overweight adults on reduced-calorie diets for two years. Those assigned 25 percent protein lost 7.9 lb (3.6 kg) and those assigned 15 percent lost 6.6 lb (3.0 kg), a gap that did not reach significance (P above 0.20), and the protein intakes people actually ate ended up closer together than the targets.

Myth. Eating ever more protein does not bring an ever bigger effect. In the 74-trial review a meta-regression found no significant dose response with higher protein intake.

Muscle, which is the stronger reason

Across 28 trials of adults with overweight or obesity who were trying to lose weight, extra protein helped hold on to muscle mass, with a standardized difference of 0.75 (0.41 to 1.10), and risk of bias in those trials ranged from low to high. The same review found no matching benefit for muscle strength or physical function. In 13 trials in women, whey protein shakes added 0.82 lb (0.37 kg) of lean mass (0.06 to 0.67) and did not change fat mass (minus 0.44 lb (0.20 kg), interval crossing zero). The lean mass gain was 2 lb (0.90 kg) when the women were also cutting calories.

Unsettled. The fullness argument holds for a meal and not yet for a diet. In isocaloric trials, a single protein-rich meal lowered hunger by about 7 mm on a 100 mm rating scale. In the 19 longer publications, eating more protein for weeks or months did not change hunger or fullness, apart from a fall in the gut hormone GLP-1. The authors call the long-term picture inconclusive, and none of this was a measure of weight.

Two findings that cut the other way

In 8 trials of 300 women with polycystic ovary syndrome, high-protein diets lowered fasting insulin by 2.69 uIU/mL (1.57 to 3.81) but took off no more weight than balanced diets of the same calories. Observational data from two cross-sectional studies link more animal protein with higher odds of obesity (odds ratio 1.18, 1.12 to 1.24). That design cannot tell which came first, animal protein tends to arrive with more total energy, and the review gives no absolute risk to set the ratio against.

Who should be careful

The most common cost is in the gut. In the 74-trial review, stomach and bowel side effects were more frequent on high-protein diets, though most trials reported harms poorly and the abstract gives no pooled rate.

Not for everyone. Kidneys are the question people ask about, and the answer depends on whether yours are healthy. In 22 trials of adults without chronic kidney disease, high-protein diets raised estimated kidney filtration without changing serum creatinine (standardized difference 0.08, minus 0.09 to 0.25, 19 trials, 1044 people), and without consistent signs of kidney injury. Those were short trials using creatinine-based estimates, the rise in filtration may be the kidney working harder, and long-term effects are unknown. People who already have chronic kidney disease were not in those trials, so a high-protein diet is a decision to make with the clinician treating them.

We found no card on high-protein diets in pregnancy, in children or alongside specific medicines for this question.

What expert bodies say

Europe has looked at this twice and found the evidence short both times. When the European Food Safety Authority set protein intakes in 2012, it considered body weight and judged the data insufficient to base a protein target on it. That was a decision about intake targets, not a verdict on dieting. Separately, the EU register of health claims lists as non-authorized the claim that a carbohydrate to protein ratio of 1.8 or less helps reduce body weight and body fat on an energy-restricted diet of at least 12 weeks. Non-authorized means the evidence did not meet the bar when it was assessed, which fits the small and fading effect described above.

How we searched

What would change this answer

• Trials longer than a year that measure how much protein people actually eat. Every long-term estimate above is diluted by people drifting back to their usual diet.
• A registered trial is testing a high-protein diet with resistance training for keeping fat off after weight loss, and another is testing a plant-based, protein-rich diet for weight loss in people over 55. Neither has reported.
• Trials of protein intake during weight loss on GLP-1 medicines, where losing muscle along with fat is the open question.
• Kidney outcomes measured beyond creatinine-based estimates, over years rather than weeks.

How much protein you need, where it comes from and who runs short are on the protein page.

Sources

1. ev-pwl-01 · Meta-analysis or systematic review · systematic review and meta-analysis of 24 randomized controlled trials · n = 1063
   Compared with an SP diet, an HP diet produced more favorable changes in weighted mean differences for reductions in body weight (-0.79 kg; 95% CI: -1.50, -0.08 kg), fat mass (FM; -0.87 kg; 95% CI: -1.26, -0.48 kg), and triglycerides (-0.23 mmol/L; 95% CI: -0.33, -0.12 mmol/L) and mitigation of reductions in fat-free mass (FFM; 0.43 kg; 95% CI: 0.09, 0.78 kg) and REE (595.5 kJ/d; 95% CI: 67.0, 1124.1 kJ/d).
   
   Who: adults on energy-restricted, isocaloric diets matched for fat, differing in protein and carbohydrate
   Effect: body weight -1.7 lb (95% CI -3.3 to -0.18; metric: -0.79 kg, -1.50 to -0.08); fat mass -1.9 lb (-2.8 to -1.1; metric: -0.87 kg, -1.26 to -0.48); fat-free mass +0.95 lb (0.2 to 1.7; metric: 0.43 kg, 0.09 to 0.78); resting energy expenditure +595.5 kJ/d (67.0 to 1124.1); mean duration 12.1 +/- 9.3 weeks
   Certainty: Short trials; the gain is modest next to the weight lost from the calorie deficit itself. Greater satiety reported in only 3 of 5 studies that measured it.
   Am J Clin Nutr, 2012 · checked 2026-10-06 · we read the abstract
2. ev-pwl-02 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 37 studies
   Based on 37 studies evaluating effects of dietary protein on body weight, the participants with increased protein intake (ranging from 18-59 energy percentage [E%]) were found to reduce body weight by 1.6 (1.2; 2.0) kg (mean [95% confidence interval]) compared to controls (isocaloric interventions with energy reduction introduced in certain studies).
   
   Who: adults with overweight or obesity in randomized trials of increased dietary protein
   Effect: body weight -3.5 lb (95% CI 2.6 to 4.4; metric: -1.6 kg, 1.2 to 2.0) vs isocaloric controls; larger effect in prediabetes than normoglycemia
   Certainty: Controls were isocaloric but only some trials imposed energy restriction; genotype subgroup findings rest on few trials.
   Nutrients, 2021 · checked 2026-10-06 · we read the abstract
3. ev-pwl-03 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 74 trials
   Pooled effect sizes using standardised mean differences (SMDs) were small to moderate and favoured higher-protein diets for weight loss (SMD -0.36, 95% confidence interval (CI) -0.56 to -0.17), body mass index (-0.37, CI -0.56 to 0.19), waist circumference (-0.43, CI -0.69 to -0.16), blood pressure (systolic: -0.21, CI -0.32 to -0.09 and diastolic: -0.18, CI -0.29 to -0.06), high-density lipoproteins (HDL 0.25, CI 0.07 to 0.44), fasting insulin (-0.20, CI -0.39 to -0.01) and triglycerides (-0.51, CI -0.78 to -0.24).
   
   Who: adults in randomized trials comparing higher- and lower-protein diets
   Effect: weight loss SMD -0.36 (95% CI -0.56 to -0.17); BMI SMD -0.37; waist circumference SMD -0.43 (-0.69 to -0.16)
   Certainty: Standardized mean differences, not kilograms; authors call the effects small.
   Eur J Clin Nutr, 2012 · checked 2026-10-06 · we read the abstract
4. ev-pwl-04 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 74 trials
   Adverse gastrointestinal events were more common with high-protein diets. Multivariable meta-regression analysis showed no significant dose response with higher protein intake.
   
   Who: adults in randomized trials comparing higher- and lower-protein diets
   Effect: adverse gastrointestinal events more frequent with high-protein diets; no significant dose response in meta-regression; no significant effect on kidney or bone surrogates
   Certainty: Harms poorly reported in most trials; no pooled rate given in the abstract.
   Eur J Clin Nutr, 2012 · checked 2026-10-06 · we read the abstract
5. ev-pwl-05 · Meta-analysis or systematic review · meta-analysis of 32 weight loss studies with at least 12 months of follow-up · n = 3492
   A recommendation to consume a lower carbohydrate, higher protein diet in mostly short term intensive interventions with long term follow up was associated with better weight and fat loss but the effect size was small-standardised means of 0.14 and 0.22, p = 0.008 and p < 0.001 respectively (equivalent to 0.4 kg for both).
   
   Who: adults in weight loss studies with at least 12 months of follow-up
   Effect: weight SMD 0.14 and fat SMD 0.22 (about 0.88 lb (0.4 kg) each); fat mass 2 vs 0.66 lb (0.9 vs 0.3 kg) when protein difference at 12 months was 5% of energy or more vs less
   Certainty: Mostly short intensive interventions with long follow-up; adherence to the higher-protein advice faded over time.
   Nutr Metab Cardiovasc Dis, 2014 · checked 2026-10-06 · we read the abstract
6. ev-pwl-06 · Randomized controlled trial(s) · randomized controlled trial, 2x2 factorial, 2 years (POUNDS Lost) · n = 811
   By 2 years, weight loss remained similar in those who were assigned to a diet with 15% protein and those assigned to a diet with 25% protein (3.0 and 3.6 kg, respectively); in those assigned to a diet with 20% fat and those assigned to a diet with 40% fat (3.3 kg for both groups); and in those assigned to a diet with 65% carbohydrates and those assigned to a diet with 35% carbohydrates (2.9 and 3.4 kg, respectively) (P>0.20 for all comparisons).
   
   Who: overweight adults randomized to four reduced-calorie diets with 15% or 25% energy from protein
   Effect: 2-year weight loss 6.6 lb (3.0 kg) (15% protein) vs 7.9 lb (3.6 kg) (25% protein), P>0.20
   Certainty: Achieved protein intakes converged more than the targets; attendance predicted weight loss far more than diet composition.
   N Engl J Med, 2009 · checked 2026-10-06 · we read the abstract
7. ev-pwl-07 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials (47 studies, 3218 participants overall) · n = 1989
   Results indicated that increased protein intake significantly prevents muscle mass decline in adults with overweight or obesity aiming for weight loss (SMD 0.75; 95% CI 0.41 to 1.10; p < 0.001).
   
   Who: adults with overweight or obesity aiming for weight loss
   Effect: muscle mass SMD 0.75 (95% CI 0.41 to 1.10); no significant effect on muscle strength or physical function; intake above 1.3 g/kg/day expected to increase muscle mass, below 1.0 g/kg/day linked to higher risk of decline
   Certainty: Risk of bias in the muscle mass trials ranged from low to high.
   Clin Nutr ESPEN, 2024 · checked 2026-10-06 · we read the abstract
8. ev-pwl-08 · Meta-analysis or systematic review · systematic review and meta-analysis of 22 randomized controlled trials with GRADE · n = 1044
   High-protein diets did not significantly change serum creatinine (19 trials; n = 1044; standardised mean difference 0.08, 95% confidence interval -0.09 to 0.25; I 2 = 20.8%), without consistent biochemical evidence suggestive of renal injury.
   
   Who: adults without chronic kidney disease in randomized trials of high-protein (about 25-35% of energy or at least 2.0 g/kg/day) vs normal or low-protein diets
   Effect: eGFR SMD 0.39 (95% CI 0.09 to 0.69, I2 74.9%); serum creatinine SMD 0.08 (-0.09 to 0.25; 19 trials, n=1044); body fat percentage and fat mass reduced, fat-free mass unchanged
   Certainty: Short trials using creatinine-based estimates; the eGFR rise may reflect hyperfiltration. Does not apply to people who already have chronic kidney disease.
   Diabetes Obes Metab, 2026 · checked 2026-10-06 · we read the abstract
9. ev-pwl-09 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 68 publications
   Long-term ingestion of protein did not affect these outcomes, except for GLP-1 which showed a significant decrease.
   
   Who: healthy adults in isocaloric randomized trials, 49 acute and 19 long-term publications
   Effect: acute: hunger -7 mm VAS, fullness +10 mm, ghrelin -20 pg/ml; long-term: no effect on these outcomes except a decrease in GLP-1
   Certainty: Appetite ratings, not weight; long-term results called inconclusive by the authors.
   Physiol Behav, 2020 · checked 2026-10-06 · we read the abstract
10. ev-pwl-10 · Meta-analysis or systematic review · systematic review and meta-analysis of 8 trials · n = 300
    However, HPDs and BDs had comparable effects on weight loss, abdominal adiposity, lipid profiles, and reproductive hormones (all P ≥ 0.05).
    
    Who: women with polycystic ovary syndrome
    Effect: fasting insulin -2.69 uIU/mL (95% CI -3.81 to -1.57); HOMA-IR -0.41; weight loss and abdominal adiposity comparable (all P >= 0.05)
    Certainty: Small trials; high heterogeneity for HOMA-IR (I2 94%).
    Nutr Diabetes, 2024 · checked 2026-10-06 · we read the abstract
11. ev-pwl-11 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 13 trials
    Globally, WP supplementation increased lean mass (WMD, 0.37 kg; 95% confidence interval [CI], 0.06 to 0.67) while not influencing changes in fat mass (-0.20 kg; 95%CI, -0.67 to 0.27) relative to non-WP control.
    
    Who: women in 13 randomized trials of whey protein with or without energy restriction or resistance training
    Effect: lean mass +0.82 lb (95% CI 0.13 to 1.5; metric: 0.37 kg, 0.06 to 0.67); fat mass -0.44 lb (-1.5 to 0.6; metric: -0.20 kg, -0.67 to 0.27); with energy restriction lean mass +2 lb (0.68 to 3.3; metric: 0.90 kg, 0.31 to 1.49)
    Certainty: 28 groups across 13 trials; few comparisons per subgroup.
    Nutr Rev, 2018 · checked 2026-10-06 · we read the abstract
12. ev-pwl-12 · Observational data · systematic review and meta-analysis of observational studies · n = 11 studies
    The meta-analysis indicated an increased likelihood of obesity with API in two cross-sectional studies (OR 1.18; 95 %CI 1.12-1.24; p < 0.001; I2: 0 %).
    
    Who: people aged 8 to 89 years in observational studies, 55% female
    Effect: obesity OR 1.18 (95% CI 1.12 to 1.24, I2 0%) in two cross-sectional studies
    Certainty: Cross-sectional, so cause and direction cannot be told apart; animal protein travels with total energy intake.
    Nutr Metab Cardiovasc Dis, 2025 · checked 2026-10-06 · we read the abstract
13. ev-pwl-13 · Position of an expert body · EFSA NDA Panel opinion on dietary reference values for protein, press release of 9 February 2012 · n = -
    The Panel also looked at several health outcomes that may be associated with protein intake – such as bone health, body weight, muscle mass and kidney function – but concluded that the available data were insufficient to derive PRIs based on these health outcomes.
    
    Who: adults in the European Union
    Effect: body weight judged insufficient as a criterion for protein reference intakes
    Certainty: A statement about setting intake targets, not a verdict on whether high-protein diets help weight loss.
    EFSA sets population reference intakes for protein, European Food Safety Authority, 2012 · checked 2026-10-06 · we read the full text
14. ev-pwl-14 · Position of an expert body · EU Register on nutrition and health claims, claim POL-HC-8505, snapshot of 2026-09-21 · n = -
    POL-HC-8505 A carbohydrate:protein (CHO:P) ratio ≤ 1.8 on an energy basis in the context of an energy-restricted diet and body weight Helps to achieve a reduction in body weight and body fat when consumed as part of an energy restricted diet (< 8,368 kJ/2,000 kcal/day) for a minimum of 12 weeks. -/- Non-authorised
    
    Who: -
    Effect: claim non-authorized
    Certainty: Non-authorized means the evidence did not meet the bar at assessment, not that there is no effect.
    EU Register on nutrition and health claims, claim POL-HC-8505, snapshot 2026-09-21 · checked 2026-10-06 · we read the section
15. ev-wpm-12 · Meta-analysis or systematic review · systematic review and meta-analysis of 22 randomized controlled trials with GRADE · n = 1044
    High-protein diets were associated with increases in eGFR without consistent biochemical evidence of renal injury in adults without chronic kidney disease.
    
    Who: adults without chronic kidney disease, high-protein diets of about 25-35% of energy or at least 2.0 g/kg/day
    Effect: eGFR SMD 0.39 (0.09 to 0.69); serum creatinine SMD 0.08 (-0.09 to 0.25; 19 trials, n=1044)
    Certainty: High-protein diets in general, not whey shakes specifically; short trials with creatinine-based estimates.
    Diabetes Obes Metab, 2026 · checked 2026-10-06 · we read the abstract