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Whey protein

Milk proteins from whey, a cheese-making by-product, found in most protein powders. People take it hoping to build muscle, stay strong with age or lose weight.

Explained simply · Last reviewed

What it is

Whey protein is a mix of proteins taken from whey, the liquid left over when cheese is made from cow’s milk. That is how EFSA, the European Union’s food safety agency, describes it. NIH’s Office of Dietary Supplements (ODS) says most protein powders and drinks contain whey, one of the complete proteins isolated from milk. A 2023 review of whey in older adults notes that it contains all the essential amino acids, including leucine.

More about Whey protein

That is how EFSA, the European Union’s food safety agency, describes it. NIH’s Office of Dietary Supplements (ODS) says most protein powders and drinks contain whey, one of the complete proteins isolated from milk. A 2023 review of whey in older adults notes that it contains all the essential amino acids, including leucine.

EFSA lists three main kinds sold: concentrates, isolates, and hydrolysates, which are partly pre-digested. A 2023 review of whey in older people with sarcopenia describes its trials: whey was taken alongside resistance training, and the comparison group got a carbohydrate supplement such as maltodextrin, or training alone.

The sections below report what reviews and health authorities have found for muscle growth compared with other proteins, muscle in older adults, recovery after exercise, body weight, and markers of blood sugar, blood fats and blood pressure.

Also known as: whey, whey protein powder, whey protein concentrate, whey protein isolate, whey protein hydrolysate, protein powder

At a glance

Safety: known risks and 3 groups who should avoid it or take extra care. See Safety ↓

Claims made about Whey protein, and how strong the evidence is for each:

Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate

Safety

Read this before the ratings below.

Risks

  • A 2025 review of trials in older adults found higher fasting insulin and higher insulin resistance (HOMA-IR) with whey than with a control, from six and four trials. Fasting blood sugar did not change. The authors say this calls for careful study of whey’s metabolic effects in longer trials, to find out whether it poses risks for this age group.
  • A 2023 umbrella review of 13 earlier reviews found that only one of them reported on safety. In that review, one trial reported mild diarrhea in four people taking whey and three taking the comparison, and wind in two people taking whey; four other trials reported no adverse events. The umbrella review’s authors call for future research to report safety. It was funded by the Whey Protein Research Consortium.
  • NIH’s Office of Dietary Supplements (ODS), writing about protein in general, says the Food and Nutrition Board has not set an upper limit for protein, because the risk of harm from too much protein in food is very low. It advises caution for people getting high protein intakes from foods and supplements, because data on possible harms are limited.

Who should avoid it or take extra care

  • Milk allergy: the US Food and Drug Administration (FDA) lists milk among the major food allergens and names whey, with casein, as milk proteins whose names do not show that they come from milk. It says the labels of most packaged foods must name milk as the source, for example as “whey (milk)”, and advises people with food allergies to read the whole ingredient list every time they buy a product.
  • Lactose intolerance: the NHS lists diet and protein shakes among the processed foods that can contain lactose, the sugar in milk that causes symptoms such as tummy pain and bloating in people with lactose intolerance.
  • Kidney disease: NIDDK, the US agency for kidney diseases, says that some people with chronic kidney disease may need to eat moderate amounts of protein so that waste does not build up in the blood, while too little protein can lead to malnutrition. It advises working with a dietitian or health professional on how much protein, and from which sources, to eat. Its advice is about protein in general and does not mention protein supplements.

Safety sources: Source [1]Source [2]Source [3]Source [4]Source [5]Source [6]

What the evidence says

Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.

  • Builds muscle mass and strength during resistance training, beyond what protein in general provides Evidence rating: Insufficient

    People who lift weights take it hoping to build more muscle and get stronger.

    EFSA, the EU food safety agency, concluded in 2010 that whey had not been shown to build muscle beyond protein’s known role, or to increase strength during resistance training.

    This claim compares whey with other sources of protein, the way EFSA, the European Union’s food safety agency, framed it. In 2010 EFSA assessed health claims that whey supports muscle growth and strength. It notes that it had already accepted a claim that protein in general helps grow and maintain muscle. So it asked whether whey does anything more.

    For muscle mass, EFSA found only three small human studies that bore on that question. They compared whey with casein or soy protein, and their results conflicted. EFSA concluded that an effect of whey on muscle mass, over and above the well-established role of protein, had not been established.

    For strength, the same three studies again conflicted. EFSA set aside two trials that compared whey with isocaloric carbohydrate supplements (supplements with the same calories), because they did not control how much protein each group got. It concluded that a link between whey taken during resistance training and greater strength had not been established.

    EFSA’s opinion dates from 2010 and rests on the studies submitted to it. This page found no review of whey in younger adults that it could read in full and use, so it rates the claim insufficient: the cited evidence is too limited to show whether whey adds anything here. Results in older adults are under the next claim.

    Sources: Source [1]

  • Helps older adults gain muscle mass and strength, including those with sarcopenia Evidence rating: Limited

    Older adults take it hoping to keep or rebuild muscle and strength as they age.

    Reviews in older adults found small gains in some measures of muscle or strength and none in others, and the two that graded their evidence rate it low to very low certainty.

    This claim is about muscle mass and strength in adults over 60, including those with sarcopenia, the age-related loss of muscle mass and strength. A 2023 review pooled trials in older people with sarcopenia. In every trial both groups did resistance training, and one group also took whey. Muscle measured as an appendicular muscle index (muscle in the arms and legs, scaled to body size) rose slightly more with whey. A second measure of limb muscle did not differ significantly. Grip strength rose by about 2.3 kg more with whey.

    The reviewers call the muscle gain small, and say the grip-strength gain did not reach the smallest change considered clinically important. They rate the muscle evidence low certainty and the grip-strength evidence very low. Most of their trials added leucine (an amino acid), vitamins or minerals to the whey, so the results are for whey products rather than whey alone. Results on walking speed and other physical tests were mixed, and there were too few trials to pool them.

    A second 2023 review covered older adults with and without sarcopenia or frailty. Across all its trials, whey alone did not significantly change lean mass or strength. In its subgroups, lean mass rose in people with sarcopenia or frailty, and strength rose in trials where both groups did resistance exercise. Physical function, mostly walking speed, improved. The reviewers rate the evidence low or very low certainty. One author discloses grants from organizations including the US National Dairy Council, Dairy Farmers of Canada and Nestle Health Sciences.

    A 2025 review of 25 trials in older adults found a gain in lower-body strength with whey, and no significant change in upper-body strength, lean mass or fat mass. Its authors call the strength effect moderate in their conclusion and small in their discussion, and their funnel plot and statistical test both suggest publication bias for that result. The review included trials of whey enriched with leucine. The review’s abstract and its results disagree about which subgroup, with or without resistance training, showed the gains, so this page reports neither.

    The comparison groups in these reviews got training alone, a carbohydrate placebo such as maltodextrin, collagen, or no supplement; the 2025 review says it did not compare whey with other proteins. The reviews disagree on lean mass, and the two that graded their evidence rate it low or very low certainty. This page rates the claim limited.

    Sources: Source [1]Source [2]Source [3]

  • Speeds recovery of muscle strength after resistance exercise Evidence rating: Limited

    People who train hard take it hoping their muscles will bounce back faster between workouts.

    A 2018 review of small trials, mostly in young men, found faster strength recovery with whey at some time points, and its authors warn against treating the result as definitive.

    A 2018 review pooled 13 small randomized trials, from eight studies, in 152 healthy young adults; about nine in ten were men. People did strenuous resistance exercise and took whey after the exercise, before it, or both, depending on the trial. In all but one study the comparison was a drink, most often a carbohydrate drink; some used collagen, milk or water. Their thigh-muscle strength was tracked over the next four days.

    The review’s summary reports small to medium benefits for whey from within a day to four days after exercise. Its results show the benefit was statistically significant at some of those time points and not at others. Half of the included studies reported a benefit and half did not. No study found that whey reduced muscle soreness or a blood marker of muscle damage.

    The authors say the review is limited to eight studies and underpowered, and they caution against reading the overall effect as definitive evidence. It was supported by Food Health Ireland, which the authors also list among their affiliations; they declare no conflicts of interest.

    In 2010 EFSA, the EU food safety agency, concluded that a link between whey and faster recovery from muscle fatigue had not been established, because none of the references submitted to it allowed a conclusion. This page rates the claim limited: a few small trials, which the review’s own authors call not definitive.

    Sources: Source [1]Source [2]

  • Helps with weight loss or reducing body fat Evidence rating: Insufficient

    People take it hoping it will help them lose weight or body fat.

    EFSA found in 2010 that weight or fat-loss benefits from whey had not been established, and later reviews report mostly no difference in body weight or fat.

    In 2010 EFSA, the EU food safety agency, assessed claims that whey helps people manage their weight, makes them feel full enough to eat less, and reduces body fat during dieting and resistance training. It concluded that none of these effects had been established. The fullness studies tested whey on a single occasion, not with repeated use. For fat loss while dieting, the one relevant trial found more fat loss with casein, another milk protein, than with whey.

    A 2023 umbrella review gathered 13 earlier reviews of whey and diabetes risk factors. It concluded that whey did not differentially affect body weight, body mass index or waist size: most of the reviews found no difference, and a few found reductions. It was funded by the Whey Protein Research Consortium, and two of its authors disclose funding from the consortium.

    In older adults, a 2025 review found no significant change in fat mass, body fat percentage or waist size with whey, compared with a placebo or non-protein control. This page rates the claim insufficient: the cited evidence is too limited to show whether whey helps with weight or fat loss.

    Sources: Source [1]Source [2]Source [3]

  • Improves blood sugar markers such as fasting glucose, insulin and HbA1c Evidence rating: Insufficient

    People with high blood sugar or type 2 diabetes take it hoping it will bring their blood sugar down.

    Reviews disagree: one found lower insulin and HbA1c that lost significance after adjustment, others found no change or higher insulin, and certainty is low.

    This claim is about laboratory markers of blood sugar control, not about diabetes complications. A 2020 review pooled 22 trials in people with metabolic syndrome or related conditions, such as overweight, type 2 diabetes or high blood pressure. It found lower fasting insulin, lower HbA1c (a measure of average blood sugar) and lower insulin resistance (HOMA-IR) with whey, and no effect on fasting blood sugar. It rates the insulin and HbA1c evidence moderate certainty, and the fasting blood sugar and insulin resistance evidence low.

    After the reviewers allowed for how much the trials varied, none of the blood sugar results remained statistically significant. They say whey’s effect on blood sugar control still has to be shown in future studies. Some of their trials gave whey inside a fortified yoghurt, a mixed diet, a drink with added fiber, or with lycopene, not as whey alone.

    A 2025 review of trials in adults, pooling 8 of them for insulin resistance, found no effect of whey on it. A 2025 review in older adults found no change in fasting blood sugar, but higher fasting insulin and insulin resistance with whey, and its authors call for research into possible risks. Both 2025 reviews compared whey with a placebo or non-protein control, and both say they did not compare whey with other proteins.

    A 2023 umbrella review, funded by the Whey Protein Research Consortium, concluded that whey may improve blood sugar markers in people with overweight, obesity or metabolic syndrome. It says the low to very low certainty of that evidence calls for caution. Because the reviews disagree, this page takes the lower rating: insufficient.

    Sources: Source [1]Source [2]Source [3]Source [4]

  • Lowers blood cholesterol and triglycerides Evidence rating: Limited

    People take it hoping it will lower their cholesterol.

    Two reviews found lower total cholesterol, but only one found lower triglycerides overall; a review in older adults found no change, and certainty is low or very low where graded.

    This claim is about blood fats, which are markers, not heart attacks or strokes. The 2020 review of 22 trials in people with metabolic syndrome or related conditions found lower triglycerides, total cholesterol and LDL (“bad”) cholesterol with whey, and no change in HDL (“good”) cholesterol. It rates the triglyceride, total cholesterol and LDL evidence low certainty, and the HDL evidence very low.

    A 2025 review of 21 trials in adults found lower total cholesterol with whey. Across all its trials, LDL cholesterol, HDL cholesterol and triglycerides did not change significantly. In some subgroups, including trials lasting 12 weeks or more, triglycerides were lower, and so was HDL. LDL was lower in people under 50 and when whey was combined with exercise. The review’s conclusion says whey was shown to lower LDL cholesterol, while its results report the overall LDL change as not significant. This page reports both and does not choose between them.

    A 2025 review in older adults found no significant change in triglycerides or in any cholesterol measure. A 2023 umbrella review, funded by the Whey Protein Research Consortium, describes the effects on blood fats as favorable or neutral, and says the low to very low certainty calls for caution.

    Of the three reviews that pooled trials, only the 2020 review found lower triglycerides across all its trials. Both 2025 reviews compared whey with a placebo or non-protein control and say they did not compare it with other proteins. This page rates the claim limited: the reviews that found lower levels rate that evidence low or very low certainty, or did not grade it, and the review in older adults found no change.

    Sources: Source [1]Source [2]Source [3]Source [4]

  • Lowers blood pressure Evidence rating: Insufficient

    People with high blood pressure take it hoping it will bring their readings down.

    A 2025 review found no significant overall change in blood pressure, though its conclusion says whey lowered the top number, and an umbrella review urges caution.

    This claim is about blood pressure readings. A 2025 review of 21 trials pooled 12 of them for blood pressure, comparing whey with a carbohydrate-based control or placebo such as maltodextrin; it says it did not compare whey with other proteins. Across all its trials, neither systolic (the top number) nor diastolic (the bottom number) pressure changed significantly. In people under 50, systolic pressure was lower with whey.

    The review’s results and its conclusion do not match. The results report no significant overall effect on blood pressure, while the conclusion says whey supplementation was shown to lower systolic pressure. This page reports both and does not choose between them.

    A 2023 umbrella review, funded by the Whey Protein Research Consortium, reports that two earlier reviews found lower systolic and diastolic pressure with whey in people with overweight or obesity. It says those findings should be read with caution, because it rated those two reviews low and moderate quality. This page rates the claim insufficient: the cited evidence is too limited to show whether whey lowers blood pressure.

    Sources: Source [1]Source [2]

How and when to take it

What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.

  • The older-adult muscle evidence is mostly for whey taken alongside resistance training

    In the 2023 review of older people with sarcopenia, every trial compared whey plus resistance training with resistance training alone or with a placebo. In a second 2023 review of older adults, whey did not improve strength across all trials; the review reports gains in some subgroups, including trials where both groups did resistance exercise. Source [1]Source [2]

Which form the evidence used

Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.

  • Whey protein concentrate, isolate or hydrolysate, What the sources supportDetails

    EFSA, the EU’s food safety agency, describes three main commercial forms: concentrates (29–89% protein by weight), isolates (about 90% protein) and hydrolysates, which are partly pre-digested. The 2023 review of whey in older people with sarcopenia included trials of isolated or hydrolysed whey, and four of its seven trials did not report which type they used. Most of its trials also added leucine (an amino acid), vitamins or minerals to the whey. No cited source compared the forms with each other, so this page cannot say that one works better than another. Source [1]Source [2]

  • Whey with added vitamin D, What the sources supportDetails

    A 2023 review of older adults analyzed whey taken with vitamin D separately from whey alone. Whey with vitamin D improved lean mass, strength and physical function, while whey alone did not significantly change lean mass or strength across all its trials. The reviewers propose that the difference likely comes from correcting low vitamin D levels, and they rate the evidence for both comparisons low or very low certainty. Source [1]

Sources

  1. Scientific Opinion on the substantiation of health claims related to whey protein and increase in satiety leading to a reduction in energy intake (ID 425), contribution to the maintenance or achievement of a normal body weight (ID 1683), growth or maintenance of muscle mass (ID 418, 419, 423, 426, 427, 429, 4307), increase in lean body mass during energy restriction and resistance training (ID 421), reduction of body fat mass during energy restriction and resistance training (ID 420, 421), increase in muscle strength (ID 422, 429), increase in endurance capacity during the subsequent exercise bout after strenuous exercise (ID 428), skeletal muscle tissue repair (ID 428) and faster recovery from muscle fatigue after exercise (ID 423, 428, 431), pursuant to Article 13(1) of Regulation (EC) No 1924/2006
    EFSA Panel on Dietetic Products, Nutrition and Allergies (EFSA Journal), 2010 · Health authority summary · Primary source
  2. Effectiveness of Whey Protein Supplementation during Resistance Exercise Training on Skeletal Muscle Mass and Strength in Older People with Sarcopenia: A Systematic Review and Meta-Analysis
    Nutrients, 2023 · Meta-analysis · Primary source · Certainty: very low
  3. Whey Protein Supplementation with or without Vitamin D on Sarcopenia-Related Measures: A Systematic Review and Meta-Analysis
    Advances in Nutrition, 2023 · Meta-analysis · Primary source · Certainty: very low
    Some of its authors disclose ties to industry.
  4. Effects of Whey Protein Supplementation on Body Composition, Muscular Strength, and Cardiometabolic Health in Older Adults: A Systematic Review with Pairwise Meta-Analysis
    Healthcare, 2025 · Meta-analysis · Primary source
  5. The Effect of Whey Protein Supplementation on the Temporal Recovery of Muscle Function Following Resistance Training: A Systematic Review and Meta-Analysis
    Nutrients, 2018 · Meta-analysis · Primary source
  6. Whey Protein Supplementation and Type 2 Diabetes Mellitus Risk Factors: An Umbrella Systematic Review of Randomized Controlled Trials
    Current Developments in Nutrition, 2023 · Systematic review · Primary source
    This source discloses industry funding.
    Some of its authors disclose ties to industry.
  7. Effects of whey protein on glycemic control and serum lipoproteins in patients with metabolic syndrome and related conditions: a systematic review and meta-analysis of randomized controlled clinical trials
    Lipids in Health and Disease, 2020 · Meta-analysis · Primary source · Certainty: very low
  8. The effects of whey protein supplementation on indices of cardiometabolic health: A systematic review and meta-analysis of randomized controlled trials
    Clinical Nutrition, 2025 · Meta-analysis · Primary source
  9. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals
    NIH Office of Dietary Supplements, 2024 · Health authority summary · Primary source
  10. Have Food Allergies? Read the Label
    U.S. Food and Drug Administration, 2023 · Health authority summary · Primary source
  11. Lactose intolerance
    NHS, 2026 · Health authority summary · Primary source
  12. Healthy Eating for Adults with Chronic Kidney Disease
    National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 2025 · Health authority summary · Primary source

Page history

Show all 4 changes to this page
  • — Drafted. Muscle in older adults, recovery after exercise, and blood cholesterol and triglycerides rated limited; muscle beyond protein in general, body weight and fat, blood sugar markers and blood pressure rated insufficient.
  • — Review round 1: corrected the strength subgroups in the how-to-take note, removed a fact-sheet sentence on high-protein diets and kidneys that dropped its scope, and stated each review’s comparison groups, mixed products, publication bias and contradictory figures more fully. No rating changed.
  • — Review round 2: corrected how the cholesterol claim describes one review’s triglyceride subgroups, and reworded the how-to-take note on strength subgroups. No rating changed.
  • — Published.