Casein vs Whey Protein: Which Should You Take?

Over weeks of training, neither protein has clearly beaten the other for muscle gain^{1, 2}. Whey digests faster and raised muscle protein synthesis more than casein in several small single-dose trials^{3, 4}. Casein digests slowly, which suits a dose before bed^{5, 6}. Supplement gains level off once total intake passes about 1.6 g of protein per kg a day⁷.

Both come from cow's milk, so neither is safe with a milk allergy^{8, 9}. Our evidence pages cover whey protein and casein protein in full.

Casein makes up 80% of milk protein and whey the other 20%¹⁰. Whey is the liquid that drains off when milk becomes cheese, strained yogurt or casein, and casein is the protein that stays in the curd^{11, 10}.

• Digestion speed: Whey causes a short, sharp rise in blood amino acids. Casein causes a lower, longer plateau because it leaves the stomach slowly⁵.
• Leucine: Whey has more leucine. In 48 older men, higher peak blood leucine went with higher muscle protein synthesis (r = 0.66)⁴.
• Protein breakdown: A casein meal cut whole-body protein breakdown by 34%. A whey meal did not⁵.
• Fullness: Whey fills you up more in the short term. Casein may last longer (see the weight-loss section below)¹⁰.

Greek yogurt is milk with the whey strained off. One analysis found the drained whey held almost no protein (0.02% w/v true protein nitrogen), so the milk proteins, mostly casein, stay in the yogurt^{11, 10}.

Whey led in several small single-dose trials, but two trials found no difference. Over weeks of training the two are close, and no large head-to-head trial separates them. A review of the field concluded that whey stimulates muscle protein synthesis more than casein or soy¹².

What happens after one dose?

• Young men after leg exercise: Muscle protein synthesis was about 122% higher after whey than after casein, with soy in between. The trial gave 10 g of essential amino acids to 18 men³.
• Older men, 20 g: Synthesis was 0.15%/h after whey and 0.08%/h after casein in 48 men aged 74⁴. After leg exercise, 14 older men reached 0.059%/h on whey protein isolate and 0.035%/h on micellar casein¹³.
• Young men after lifting plus cycling: With 45 g of carbohydrate, 20 g of whey and 20 g of casein gave the same rates (0.054%/h vs 0.059%/h) in 48 men. Either protein beat carbohydrate alone, 0.057%/h vs 0.049%/h¹⁴.

What happens over weeks of training?

• Head-to-head, 8 weeks: In 16 female college basketball players taking 24 g before and after training, whey and casein produced the same change in lean mass (+1.5 kg vs +1.4 kg). It is a small trial¹.
• Network meta-analysis of 36 trials: Against placebo, whey added 1.24 kg of lean mass and casein 0.92 kg. The comparison is indirect, and the authors call the dose estimates exploratory¹⁵.
• Network meta-analysis of 116 trials in 4,711 adults: Milk proteins, including whey and casein, improved muscle mass and strength. The authors say direct comparisons are still needed².
• Total protein: Across 49 trials in 1,863 people, supplements added 0.30 kg of fat-free mass. Gains levelled off at total intakes above 1.62 g/kg a day, and the benefit shrank with age⁷.

Does age change the answer?

The evidence is mixed. In the 36-trial analysis, casein's ranking rose in adults 65 and older, but that rested on only nine trials¹⁵. In a 12-week trial of 41 men around age 70, protein after exercise and before sleep added nothing to strength or muscle size¹⁶.

For the detail on each protein, see whey protein for muscle protein synthesis and casein protein for muscle protein synthesis.

Casein is the studied pre-bed protein, but whey did just as well in the one trial that compared them.

• Overnight synthesis: In 16 young men, 40 g of casein 30 minutes before sleep raised whole-body protein synthesis (311 vs 246 μmol/kg over 7.5 hours). Muscle synthesis rose about 22%, a borderline result (P = 0.05)⁶.
• Casein vs whey at night: In 36 young men after evening endurance exercise, 45 g of casein and 45 g of whey raised overnight muscle protein synthesis equally (0.056%/h vs 0.064%/h)¹⁷.
• 12 weeks of training: 44 young men who took 27.5 g of protein before sleep gained more thigh muscle area (+8.4 cm² vs +4.8 cm²) than those on placebo¹⁸.
• Older men: A review of nine studies found muscle and strength benefits in young but not older men, and asked for more data¹⁹.

A network meta-analysis found night-time protein best for strength (leg press +12.12 kg) and protein after exercise best for fat-free mass (+0.54 kg), both against placebo².

When to take casein vs whey

• After training: Whey fits, because its amino acids arrive fast. The older-men trials above used 20 g⁴.
• Before bed: The studied dose is 20-40 g of casein about 30 minutes before sleep¹⁹. Whey also worked at 45 g¹⁷.
• Between meals: Casein's slow release kept amino acids raised for hours in a single-meal study, so it may suit long gaps⁵.
• Total intake: Supplement gains levelled off above 1.62 g/kg a day, so check your daily total before fine-tuning timing⁷.

Whey fills you up faster, casein may keep you full longer, and neither changed body weight in trials lasting weeks.

• One meal: Participants ate less at a buffet 90 minutes after a 48 g whey drink than after 48 g of casein. Whey raised blood amino acids by 28%, cholecystokinin by 60% and GLP-1 by 65%²⁰.
• 12 weeks: In 70 overweight or obese adults, whey raised fullness before lunch compared with casein or glucose. It did not change energy intake or body weight²¹.
• Body composition: Whey did not change body composition over 12 weeks compared with casein or control, though LDL cholesterol fell versus casein (P = 0.045)²².
• Calorie-restricted diet: Obese volunteers lost 7.5 kg, including 5.1 kg of fat and 2.2 kg of lean mass, over 6 weeks. Casein and whey groups did not differ²³.

A review of controlled trials reached the same split: whey is more satiating in the short term and casein in the long term. It found no clear evidence that either improved weight or body composition more¹⁰.

Our pages on whey protein for weight loss support and appetite suppression cover this in more depth.

Neither is safe with a milk allergy, and lactose is a separate issue that depends on your dose.

• Lactose intolerance: This means bloating, diarrhea and gas after lactose. It is not a milk allergy, which is an immune disorder²⁴. About 68% of the world's population, and about 36% of people in the United States, malabsorb lactose²⁴.
• How much lactose is too much: 13 adults who malabsorb lactose tolerated up to 6 g. Abdominal pain began at 12 g²⁵. Check the lactose per serving on a powder's label.
• Milk allergy: The main milk allergens include the caseins and the whey proteins α-lactalbumin and β-lactoglobulin⁸. Choosing casein over whey does not avoid them.
• Adults: Of 30 adults with milk allergy, 20 (67%) reported severe symptoms. Reactions began at doses as low as 0.3 mg of milk protein⁹.

Casein is part of milk, so a casein allergy is a milk allergy⁸. Only a clinician can tell lactose intolerance from an allergy. Our pages on lactose intolerance and food allergies explain the difference.

For healthy adults, the evidence says yes, with two caveats: kidney disease and product quality.

• Kidneys: A meta-analysis of 28 trials in 1,358 healthy adults found that high-protein diets (at least 1.5 g/kg, 20% of energy or 100 g a day) did not harm filtration rate. It excluded people with kidney disease²⁶.
• Metals, modelled risk: Earlier testing had found elevated metals in 40% of 133 products. A risk model built on those reported arsenic, cadmium, mercury and lead levels found no increased health risk at one or three servings a day. Whey powders scored lowest and mass-gainer powders highest²⁷.
• Metals, measured: Across 47 whey products, 30 g a day supplied 18-26% of the reference intake for chromium and 27% for molybdenum. The hazard index stayed below 1 up to 100 g a day, but at 100 g and maximum concentrations several minerals could exceed recommended intakes. The authors asked for better labelling²⁸.

No trial ranks brands, so no study can name the safest or healthiest powder. If you have kidney disease, ask your kidney doctor before raising protein. See our page on chronic kidney disease.

For long-term gains the gap is small. After one dose, whey leads and soy sits between whey and casein.

• One dose: After exercise, whey hydrolysate raised muscle protein synthesis 31% more than soy, and soy raised it 69% more than casein³.
• Weeks of training: A meta-analysis of 9 studies in 266 people found soy and animal protein produced similar gains in strength and lean mass²⁹.
• Plant proteins overall: The 36-trial network analysis found smaller effects for plant proteins, but called the certainty low to very low¹⁵.

If you avoid dairy, see our page on pea protein, which this article did not compare directly.

• Mainly want muscle: Reach your daily total from food first, since supplement gains levelled off above 1.62 g/kg a day. Either protein is a reasonable choice^{7, 2}.
• Train and want a fast dose: Use whey around the workout⁴.
• Want something before bed: Use 20-40 g of casein, or whey if that is what you have^{19, 17}.
• Want to feel full: Whey helps for a few hours, but neither moved the scale in 12 weeks²¹.
• Have a milk allergy: Skip both⁸.

Taking creatine too? Our guide on mixing creatine with protein shakes covers it.

Related health goals

• Muscle Protein Synthesis
• Weight Loss Support
• Post-Workout Recovery

We searched PubMed and the Firecrawl research index for trials, meta-analyses and reviews on whey versus casein across muscle protein synthesis, pre-sleep dosing, fullness, allergy and safety. We read the PubMed abstracts of 28 papers and the NIDDK lactose intolerance page, and cited all of them. We favoured randomised trials and meta-analyses that compared the proteins directly.

The evidence has limits. The one-dose studies used 6 to 48 participants, and long head-to-head trials are rare. We did not read full texts or test any product. Searched on 30 October 2026.

1. Wilborn CD, et al. The Effects of Pre- and Post-Exercise Whey vs. Casein Protein Consumption on Body Composition and Performance Measures in Collegiate Female Athletes. J Sports Sci Med. 2013;12(1):74-9. https://pubmed.ncbi.nlm.nih.gov/24149728/
2. Zhou HH, et al. Effects of Timing and Types of Protein Supplementation on Improving Muscle Mass, Strength, and Physical Performance in Adults Undergoing Resistance Training: A Network Meta-Analysis. Int J Sport Nutr Exerc Metab. 2024;34(1):54-64. doi:10.1123/ijsnem.2023-0118
3. Tang JE, 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 (1985). 2009;107(3):987-92. doi:10.1152/japplphysiol.00076.2009 Our study summary.
4. Pennings B, et al. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. Am J Clin Nutr. 2011;93(5):997-1005. doi:10.3945/ajcn.110.008102
5. Boirie Y, et al. Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci U S A. 1997;94(26):14930-5. doi:10.1073/pnas.94.26.14930
6. Res PT, et al. Protein ingestion before sleep improves postexercise overnight recovery. Med Sci Sports Exerc. 2012;44(8):1560-9. doi:10.1249/MSS.0b013e31824cc363 Our study summary.
7. Morton RW, 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. doi:10.1136/bjsports-2017-097608 Our study summary.
8. Jensen SA, et al. Diagnosis and Rationale for Action against Cow's Milk Allergy (DRACMA) Guidelines update - III - Cow's milk allergens and mechanisms triggering immune activation. World Allergy Organ J. 2022;15(9):100668. doi:10.1016/j.waojou.2022.100668
9. Lam HY, 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. doi:10.1111/j.1365-2222.2008.02968.x
10. Bendtsen LQ, et al. Effect of dairy proteins on appetite, energy expenditure, body weight, and composition: a review of the evidence from controlled clinical trials. Adv Nutr. 2013;4(4):418-38. doi:10.3945/an.113.003723
11. Smith S, et al. Short communication: Flavor and flavor stability of cheese, rennet, and acid wheys. J Dairy Sci. 2016;99(5):3434-3444. doi:10.3168/jds.2015-10482
12. Devries MC, et al. Supplemental protein in support of muscle mass and health: advantage whey. J Food Sci. 2015;80 Suppl 1:A8-A15. doi:10.1111/1750-3841.12802
13. Burd NA, et al. Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men. Br J Nutr. 2012;108(6):958-62. doi:10.1017/S0007114511006271
14. Churchward-Venne TA, et al. Myofibrillar and Mitochondrial Protein Synthesis Rates Do Not Differ in Young Men Following the Ingestion of Carbohydrate with Milk Protein, Whey, or Micellar Casein after Concurrent Resistance- and Endurance-Type Exercise. J Nutr. 2019;149(2):198-209. doi:10.1093/jn/nxy244
15. Li Y, et al. Dose-structure-population interactions of protein supplementation combined with resistance training on body composition: a Bayesian network meta-analysis with dose-response modeling. Front Nutr. 2026;13:1860234. doi:10.3389/fnut.2026.1860234
16. Holwerda AM, et al. Protein Supplementation after Exercise and before Sleep Does Not Further Augment Muscle Mass and Strength Gains during Resistance Exercise Training in Active Older Men. J Nutr. 2018;148(11):1723-1732. doi:10.1093/jn/nxy169
17. Trommelen J, et al. Pre-sleep Protein Ingestion Increases Mitochondrial Protein Synthesis Rates During Overnight Recovery from Endurance Exercise: A Randomized Controlled Trial. Sports Med. 2023;53(7):1445-1455. doi:10.1007/s40279-023-01822-3
18. Snijders T, et al. Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men. J Nutr. 2015;145(6):1178-84. doi:10.3945/jn.114.208371 Our study summary.
19. Reis CEG, et al. Effects of pre-sleep protein consumption on muscle-related outcomes - A systematic review. J Sci Med Sport. 2021;24(2):177-182. doi:10.1016/j.jsams.2020.07.016
20. Hall WL, et al. Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite. Br J Nutr. 2003;89(2):239-48. doi:10.1079/BJN2002760
21. Pal S, et al. Comparative effects of whey and casein proteins on satiety in overweight and obese individuals: a randomized controlled trial. Eur J Clin Nutr. 2014;68(9):980-6. doi:10.1038/ejcn.2014.84
22. Pal S, et al. Effects of whey protein isolate on body composition, lipids, insulin and glucose in overweight and obese individuals. Br J Nutr. 2010;104(5):716-23. doi:10.1017/S0007114510000991
23. Adechian S, et al. Protein feeding pattern, casein feeding, or milk-soluble protein feeding did not change the evolution of body composition during a short-term weight loss program. Am J Physiol Endocrinol Metab. 2012;303(8):E973-82. doi:10.1152/ajpendo.00285.2012
24. National Institute of Diabetes and Digestive and Kidney Diseases. Definition & Facts for Lactose Intolerance. https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/definition-facts
25. Hertzler SR, et al. How much lactose is low lactose?. J Am Diet Assoc. 1996;96(3):243-6. doi:10.1016/S0002-8223(96)00074-0
26. Devries MC, 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. doi:10.1093/jn/nxy197
27. Bandara SB, et al. A human health risk assessment of heavy metal ingestion among consumers of protein powder supplements. Toxicol Rep. 2020;7:1255-1262. doi:10.1016/j.toxrep.2020.08.001
28. Bethencourt-Barbuzano E, et al. Whey Protein Dietary Supplements: Metal Exposure Assessment and Risk Characterization. Nutrients. 2023;15(16). doi:10.3390/nu15163543
29. Messina M, et al. No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise. Int J Sport Nutr Exerc Metab. 2018;28(6):674-685. doi:10.1123/ijsnem.2018-0071