Supplements

Whey Protein

Updated · 24 sources · Editorial policy

Whey protein is the protein fraction of whey, the liquid left over when milk is curdled to make cheese. Filtered and dried into a powder, it is the basis of most protein supplements sold for sports nutrition. It digests quickly, is rich in essential amino acids and has the highest leucine content of the common protein sources.

Whey is a food, not a drug or a hormone. Its main value is as a convenient way to reach a daily protein target. The largest meta-analysis of protein supplements during resistance training found real but modest extra gains: about 0.3 kg more fat-free mass and 2.5 kg more one-repetition-maximum strength than training alone, with no further benefit to fat-free mass once total intake passed about 1.6 g/kg/day (Morton et al., BJSM 2018).

This page summarizes what meta-analyses, controlled trials, product-testing studies and regulators report. It is for education only and is not medical advice.

Property Detail
Class Milk protein; food ingredient sold as a food or dietary supplement
Main forms Concentrate (sports products typically 70–80% protein), isolate (over 90% protein), hydrolysate (partly pre-digested into short peptides)
Route Oral powder or ready-to-drink beverages
Doses used in studies 20–40 g per serving in muscle protein synthesis studies; an average of 36 g/day (range 4–106 g) in long-term training trials
Leucine content About 11% of whey protein, vs 9.3% for casein (ISSN)
Half-life Not applicable to a dietary protein. After a 30 g dose, blood amino acids peaked strongly and returned to baseline by about 5 hours
US status Whey and whey protein concentrate are GRAS (generally recognized as safe) food ingredients under 21 CFR 184.1979 and 184.1979c; milk is a major food allergen that must be declared
WADA status Not on the 2026 Prohibited List; contamination with prohibited diuretics has been reported in some products

What it is

Milk protein can be separated into two classes: casein, which clots during cheesemaking, and whey, which stays in the liquid. US food regulations define whey as “the liquid substance obtained by separating the coagulum from milk, cream, or skim milk in cheesemaking.” On a dry basis, plain dried whey is only 10–15% protein and 61–75% lactose (milk sugar) (21 CFR 184.1979). Supplement-grade whey is made by stripping out most of that lactose and fat.

The ISSN position stand on protein describes the main forms:

Form How it is made Protein content
Concentrate (WPC) Filtration removes part of the lactose, fat and minerals Defined as 29–80% protein by dry weight; sports products generally use 70–80%. US food rules set a minimum of 25% protein and a maximum of 60% lactose (21 CFR 184.1979c)
Isolate (WPI) Extra filtration steps (micro/ultrafiltration) or ion exchange Over 90% protein
Hydrolysate (WPH) Protein pre-exposed to digestive enzymes, breaking it into di-, tri- and tetrapeptides Depends on the starting material

The ISSN notes trade-offs between processing methods. Ion exchange is cheaper and gives the highest protein purity but can denature some of whey’s minor peptides. Membrane filtration keeps those peptides intact but costs more. In one comparison, a whey peptide hydrolysate raised blood amino acids faster than intact milk proteins and produced a higher insulin peak.

The major individual whey proteins are α-lactalbumin and β-lactoglobulin, both important milk allergens (Lam et al., Clin Exp Allergy 2008).

Leucine and why whey is “fast”

Muscle needs essential amino acids (EAAs) to build new protein. The ISSN states that rapidly digested proteins with a high EAA content and adequate leucine are the most effective at stimulating muscle protein synthesis (MPS). It reports that whey and casein have the highest leucine content of the common protein sources, at about 11% and 9.3% respectively. It recommends that a protein serving contain 700–3000 mg of leucine plus a full set of EAAs.

Whey is water-soluble and digests quickly. Casein clots in the stomach and digests slowly. In the original digestion studies summarized by the ISSN, a 30 g dose of whey produced a sharp rise in blood amino acids by 100 minutes that was back to baseline by 300 minutes. A 43 g dose of casein produced a slower, longer rise.

HMB, a breakdown product of leucine, is sold separately as a supplement; see HMB. Other supplements studied alongside resistance training have their own pages, including creatine monohydrate, beta-alanine and citrulline malate.

How it works in the body

Resistance exercise and protein intake each stimulate muscle protein synthesis, and the two together have a synergistic effect. Per the ISSN, MPS peaks within about 30 minutes of a protein dose and stays raised for up to about 3 hours. The anabolic effect of a training session lasts at least 24 hours.

Short-term tracer studies, which measure MPS directly in muscle biopsies over a few hours, compared whey with other proteins and doses:

Study Design Main result
Tang et al. 2009 18 young men (6 per group); whey hydrolysate, micellar casein or soy isolate, each giving 10 g EAAs, after one-leg exercise After exercise, MPS was ≈122% higher with whey than casein and 31% higher than soy. Whey also raised blood leucine the most
Witard et al. 2014 48 resistance-trained young men (≈80 kg); 0, 10, 20 or 40 g whey isolate after leg exercise MPS rose 49% with 20 g and 56% with 40 g; 10 g gave no extra rise. Doses above 20 g increased amino acid oxidation and urea production
Macnaughton et al. 2016 30 resistance-trained young men; 20 vs 40 g whey after whole-body exercise 40 g stimulated more MPS than 20 g (0.059 vs 0.049%/h, p = 0.005), regardless of lean body mass

These are acute measurements over hours, not muscle growth over months. They explain why whey is often studied at 20–40 g per serving, but they do not by themselves show larger long-term gains.

Regulatory status

In the US, whey and whey protein concentrate are listed as GRAS food substances that may be used in food under good manufacturing practice (21 CFR 184.1979; 21 CFR 184.1979c). Many whey powders are sold as dietary supplements. Under DSHEA, the 1994 supplement law, manufacturers are responsible for the safety and labeling of their products before marketing, and FDA acts against adulterated or misbranded products after they reach the market (FDA).

Milk is one of the nine major food allergens under US law, and labels must name it, for example as “whey (milk)” (FDA).

Whey is not a prohibited substance in sport and is not listed on the WADA 2026 Prohibited List. It is not an anabolic steroid and is not named in 21 CFR 1308.13.

What the research shows

Muscle mass and strength with resistance training

The main evidence comes from Morton et al. (BJSM 2018), a systematic review and meta-analysis of 49 randomized controlled trials with 1863 participants (mean age 35). Every trial combined at least 6 weeks of resistance training with protein supplementation; programs lasted 6–52 weeks. The protein groups received an average of 36 g/day of extra protein.

This was a meta-analysis of protein supplements in general, not of whey alone. Whey was the most common source: 23 study conditions used whey, 10 milk or milk protein, 6 soy, 3 casein and 1 pea. Results compared with training plus placebo or no supplement:

Outcome Added effect of protein supplement (95% CI)
1RM strength +2.49 kg (0.64–4.33); ≈9% of the average 27 kg training-induced gain
Fat-free mass +0.30 kg (0.09–0.52)
Fat mass −0.41 kg (−0.70 to −0.13)
Muscle fiber cross-sectional area +310 µm² (51–570)
Mid-thigh cross-sectional area +7.2 mm² (0.20–14.30)
Total body mass +0.11 kg (−0.23 to 0.46); not significant
Isometric/isokinetic strength (MVC) SMD 0.04 (−0.09 to 0.16); not significant

Two factors changed the size of the effect:

  • Training experience. The added fat-free mass gain was 0.75 kg (0.09–1.40) larger in resistance-trained participants than in untrained ones.
  • Age. The benefit shrank by about 0.01 kg for each additional year of age.

The authors concluded that details such as timing, post-exercise dose and protein source played a minor role, if any, in gains over weeks. Total daily protein intake mattered more. One author (Phillips) disclosed funding from the US National Dairy Council, which also supported some included trials.

How much protein per day

The two sources most often quoted give similar targets:

Source Daily protein intake Per serving
Morton et al. 2018 (break-point analysis, 42 study arms, 723 participants) Gains in fat-free mass plateaued at 1.62 g/kg/day (95% CI 1.03–2.20). Because of the wide CI, the authors suggested ≈2.2 g/kg/day for people seeking the maximum gain ≈0.25 g/kg per dose
ISSN position stand 2017 1.4–2.0 g/kg/day for most exercising people; 2.3–3.1 g/kg/day may be needed to keep lean mass during calorie restriction in resistance-trained people 0.25 g/kg or 20–40 g, with 700–3000 mg leucine, spread every 3–4 h

For comparison, the US/Canadian recommended dietary allowance (RDA) is 0.8 g/kg/day. The average baseline intake in Morton’s trials was already about 1.4 g/kg/day, yet adding about 35 g/day still produced small extra gains.

The Morton break-point model was not statistically significant (p = 0.079), and the authors presented it as a pragmatic estimate. The ISSN also notes “novel evidence” that intakes over 3.0 g/kg/day may help fat loss in trained people. Some ISSN authors list affiliations with supplement companies.

Both sources say the protein can come from food. The ISSN describes supplements as a practical, not necessary, way to reach the target.

Whey compared with other proteins

Over weeks of training, direct comparisons are limited. In one 8-week trial of 41 men and women cited by the ISSN, 46 g/day of whey concentrate, hydrolyzed chicken protein or beef protein isolate produced similar strength gains. Morton’s authors concluded that protein source played a minor role, if any, in long-term results. Whey’s advantage is clearest in short-term MPS studies such as Tang et al..

Recovery after training

A 2018 meta-analysis pooled 13 randomized trials (from 8 studies) in young, healthy adults (Davies et al., Nutrients 2018). Whey gave small-to-medium improvements in the recovery of muscle force after strenuous resistance exercise, with effect sizes of 0.4–0.7 from under 24 hours to 96 hours. Only half of the individual studies found a benefit, and the authors called for more research.

Side effects and risks

In healthy adults, whey’s risks are mostly those of a dairy food: lactose, milk allergy and product quality. Most people tolerate it well.

Kidney function in healthy people

The concern that high-protein diets damage the kidneys comes mainly from people who already have kidney failure, who do benefit from protein restriction. The ISSN states that extending this to healthy exercising people is not supported by evidence.

A meta-analysis of 28 trials with 1358 adults without kidney disease compared higher-protein diets (≥1.5 g/kg/day, ≥20% of energy or ≥100 g/day) with normal or lower intakes (Devries et al., J Nutr 2018):

  • Glomerular filtration rate (GFR, how fast the kidneys filter blood) was slightly higher at the end of high-protein diets (SMD 0.19, 95% CI 0.07–0.31), an effect the authors called trivial.
  • The change in GFR from start to end did not differ between diets (SMD 0.11, 95% CI −0.05 to 0.27).

The authors concluded that higher protein intakes do not adversely affect kidney function in healthy adults. Trials had to last more than 4 days, and the authors noted an unclear risk of selection bias in the included trials. People with kidney disease were excluded and are a different population.

Liver

Controlled data in healthy people are reassuring. In a one-year randomized crossover study, 14 resistance-trained men alternated their usual diet (2.51 g/kg/day protein) with a high-protein diet (3.32 g/kg/day). There were no harmful effects on blood lipids, liver function or kidney function (Antonio et al., J Nutr Metab 2016). The study was small.

Rare case reports exist. A 27-year-old weightlifter developed severe cholestatic liver injury (bilirubin 54.7 mg/dL) after 4 weeks of whey protein while also taking creatine for 8–9 months; he recovered after stopping both (Whitt et al., Semin Liver Dis 2008). A single case cannot show that whey caused it. Hepatologists testing protein powders in India found that some products also contained herbal extracts linked to liver injury, such as green tea extract, turmeric, Garcinia cambogia and ashwagandha (Philips et al., Medicine 2024). Checking the full ingredient list matters, not only the protein source.

Lactose intolerance

Whey straight from cheesemaking is mostly lactose: plain dried whey is 61–75% lactose, and US rules allow whey protein concentrate to contain up to 60% lactose on a dry basis (21 CFR 184.1979c). Isolates go through more filtration to separate protein from lactose and fat (ISSN). The lactose content of a specific product is rarely stated on the label.

The NIDDK lists whey and protein powders among products that contain lactose. It notes that many people with lactose intolerance can have about 12 g of lactose, the amount in about one cup of milk, with no symptoms or only mild ones (NIDDK).

Milk allergy

Lactose intolerance and milk allergy are different. Milk allergy is an immune reaction to milk proteins, including the whey proteins themselves, so isolates and hydrolysates are still milk proteins. In a study of adults with confirmed cow’s milk allergy, 20 of 30 (67%) reported severe reactions, and symptoms could start at doses as low as 0.3 mg of milk protein. Patients reacted to both casein and whey proteins (Lam et al., Clin Exp Allergy 2008).

A case report described a 24-year-old man who developed IgE-mediated milk allergy after 2 years of taking a hydrolyzed whey and casein blend. The authors noted that adult-onset milk allergy is rarely reported (Sousa et al., Eur Ann Allergy Clin Immunol 2018).

Acne

Whether whey worsens acne has been debated, and controlled evidence is limited. In a 6-month double-blind randomized trial of 49 young men with mild-to-moderate acne, 30 g/day of whey was noninferior to a non-whey supplement for changes in acne lesion counts and severity (Sompochpruetikul et al., J Dermatol 2024). The trial was small and included only men who already had acne.

Who should be cautious

  • People with milk allergy: whey is a milk protein in every form.
  • People with chronic kidney disease or other conditions that call for protein restriction: the safety data above come from healthy adults.
  • People with lactose intolerance: concentrates carry more lactose than isolates.
  • Tested athletes: see contamination below.

Quality and contamination

Because supplements are not approved before sale, product quality varies. Independent testing studies have found several problems.

Protein content and “spiking”

Protein content is usually measured indirectly from nitrogen, using the Kjeldahl method. This means cheap non-protein nitrogen sources can make a product look richer in protein than it is, a practice called nitrogen or amino-acid spiking.

Study Products tested Findings
González-Weller et al., Foods 2023 47 whey concentrates and isolates from the EU and UK Mean measured protein 70.9% (range 18–92.3%) vs 74.3% declared; statistically significant gap and “a high degree of non-compliance” with label claims
Philips et al., Medicine 2025 34 whey powders sold in India: 16 sports/nutraceutical, 18 medical/pharmaceutical Sports powders averaged 75.6 g protein per 100 g and matched labels, with up to 8.5 g leucine per 100 g. Pharmaceutical powders averaged 29.1 g per 100 g, and 83% missed their label by more than 5%. Undeclared taurine was found in 89% of pharmaceutical and 12.5% of sports powders

The 2025 authors described the undeclared taurine as evidence of nitrogen spiking. They also noted that the amounts found (milligrams per 100 g) were too small to inflate protein readings much; the main issue was undisclosed ingredients.

Heavy metals

Heavy metals such as lead, arsenic and cadmium are commonly detectable in protein powders at low levels. Two risk assessments reached broadly reassuring conclusions for whey at normal intakes:

  • A 2020 assessment used data from a Consumer Reports analysis of 15 products and a larger survey of 133 products. It found a hazard index under 1 (no increased health risk) at one or three servings a day. The highest values were in “mass gainer” products and the lowest in whey protein powders (Bandara et al., Toxicol Rep 2020).
  • A 2026 study of 30 sports protein products sold in China found at least one target metal in every sample. Dairy-based products had lower mean lead (0.06 vs 0.18 mg/kg) and cadmium (0.01 vs 0.05 mg/kg) than plant-based ones. The hazard index was 0.45 at 30 g/day and 0.90 at 90 g/day, but the 95th-percentile estimate for heavy use was 1.28. Microplastic particles were found in all samples, 2–19 per 30 g serving (Chen et al., Environ Res 2026).

Undeclared drugs

A Brazilian university laboratory tested 21 commercial whey-based supplements for diuretics. Of these, 42.9% contained at least one. Furosemide was found in 28.8% of samples and hydrochlorothiazide in 19.0% (Franskoviaki et al., ACS Omega 2026). Both drugs are banned at all times under section S5 (diuretics and masking agents) of the WADA 2026 Prohibited List. This was a single small study. The authors cite reported cases of athletes who tested positive after using such products.

Key takeaways

  • A filtered milk protein. Concentrates are typically 70–80% protein and carry more lactose; isolates are over 90% protein; hydrolysates are partly pre-digested.
  • Fast and leucine-rich. Whey is about 11% leucine and raises muscle protein synthesis more than casein or soy in short-term studies.
  • Modest long-term gains. Across 49 trials, protein supplements (mostly whey or milk protein) added about 0.3 kg of fat-free mass and 2.5 kg of 1RM strength to resistance training, with larger effects in trained people and smaller ones in older adults.
  • Total intake matters most. Gains plateaued around 1.6 g/kg/day (upper CI 2.2) in Morton 2018, and the ISSN recommends 1.4–2.0 g/kg/day, from food or supplements.
  • No sign of kidney or liver harm in healthy adults. Trials and a meta-analysis found no adverse change in kidney function, but people with kidney disease, milk allergy or lactose intolerance are different cases.
  • Product quality varies. Testing studies have found protein below label claims, undisclosed nitrogen sources, low-level heavy metals and, in one study, prohibited diuretics.

Sources

  1. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. PubMed; PMC.
  2. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384. PubMed; PMC.
  3. Davies RW, Carson BP, Jakeman PM. The effect of whey protein supplementation on the temporal recovery of muscle function following resistance training: a systematic review and meta-analysis. Nutrients. 2018;10(2):221. PubMed.
  4. Tang JE, Moore DR, Kujbida GW, et al. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol. 2009;107(3):987–992. PubMed.
  5. Witard OC, Jackman SR, Breen L, et al. Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise. Am J Clin Nutr. 2014;99(1):86–95. PubMed.
  6. Macnaughton LS, Wardle SL, Witard OC, et al. The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein. Physiol Rep. 2016;4(15):e12893. PubMed.
  7. Devries MC, Sithamparapillai A, Brimble KS, et al. Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis. J Nutr. 2018;148(11):1760–1775. PubMed.
  8. Antonio J, Ellerbroek A, Silver T, et al. A high protein diet has no harmful effects: a one-year crossover study in resistance-trained males. J Nutr Metab. 2016;2016:9104792. PubMed.
  9. Whitt KN, Ward SC, Deniz K, et al. Cholestatic liver injury associated with whey protein and creatine supplements. Semin Liver Dis. 2008;28(2):226–231. PubMed.
  10. Lam HY, van Hoffen E, Michelsen A, et al. Cow’s milk allergy in adults is rare but severe: both casein and whey proteins are involved. Clin Exp Allergy. 2008;38(6):995–1002. PubMed.
  11. Sousa MJCS, Reis Ferreira AL, Moreira da Silva JP. Bodybuilding protein supplements and cow’s milk allergy in adult. Eur Ann Allergy Clin Immunol. 2018;50(1):42–44. PubMed.
  12. Sompochpruetikul K, Khongcharoensombat T, Chongpison Y, et al. Whey protein and male acne: a double-blind, randomized controlled trial. J Dermatol. 2024;51(7):1022–1025. PubMed.
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  14. Philips CA, Theruvath AH, Sreemohan A, et al. The Citizens Protein Project 2: the first publicly crowd-funded observational study on exhaustive analysis of popular whey protein supplements in India reveal poor quality and deceptive marketing claims of medical pharmaceutical- compared to nutraceutical- industry powders. Medicine (Baltimore). 2025;104(46):e45970. PubMed.
  15. Philips CA, Theruvath AH, Ravindran R, Chopra P. Citizens protein project: a self-funded, transparent, and concerning report on analysis of popular protein supplements sold in the Indian market. Medicine (Baltimore). 2024;103(14):e37724. PubMed.
  16. Bandara SB, Towle KM, Monnot AD. A human health risk assessment of heavy metal ingestion among consumers of protein powder supplements. Toxicol Rep. 2020;7:1255–1262. PubMed.
  17. Chen M, Dong R, Lai W. Heavy metal and microplastic exposure from sports protein supplements: integrated health risk modeling and scenario analysis. Environ Res. 2026;295:123988. PubMed.
  18. Franskoviaki IM, Ferreira PCL, Argoud VK, et al. Detection of diuretics contamination in whey protein-based dietary supplements. ACS Omega. 2026;11(6):9388–9397. PubMed.
  19. Code of Federal Regulations. 21 CFR 184.1979 (Whey) and 21 CFR 184.1979c (Whey protein concentrate). eCFR 184.1979; eCFR 184.1979c.
  20. Code of Federal Regulations. 21 CFR 1308.13, Schedule III. eCFR.
  21. National Institute of Diabetes and Digestive and Kidney Diseases. Eating, diet, and nutrition for lactose intolerance. NIDDK.
  22. US Food and Drug Administration. Food allergies. FDA.
  23. US Food and Drug Administration. Dietary supplements. FDA.
  24. World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.