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Whey Protein

Whey and casein protein are both derived from milk. Whey protein powder is extremely popular due to its high digestibility and well-researched muscle-supporting benefits.

Our evidence-based analysis on whey protein features 288 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
Last Updated:

Summary of Whey Protein

Primary information, health benefits, side effects, usage, and other important details

Quickly and easy calculate your optimal daily intake with our protein intake calculator.

What is whey protein?

Whey protein is a collection of proteins found in whey, a byproduct of cheesemaking. When a coagulant (usually renin) is added to milk, the curds (casein) and whey separate; whey protein is the water-soluble part of milk. As a supplement, it’s sold as dry powders with various levels of processing that affect how concentrated a source of protein they are and how fast they’re absorbed.

What are the benefits of whey protein?

It’s a high quality, well-absorbed source of protein that’s very useful for hitting targeted daily protein goals. Its benefits extend to the benefits of increased protein intake in general, such as augmenting muscle gain in conjunction with resistance training, limiting muscle loss during low-calorie diets, and modestly limiting fat gain during periods of excessive calorie intake. These effects aren’t exclusive to whey protein but it will likely be more effective than most other protein sources per gram.

What are whey protein’s side effects and drawbacks?

Whey does not harm the liver or kidneys, but it can exacerbate pre-existing damage. People with damaged livers or kidneys should exercise caution when increasing protein intake quickly without the guidance of a doctor. See more: can eating too much protein be bad for you?

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How to Take

Recommended dosage, active amounts, other details

To determine your optimal intake, you can use our Protein Intake Calculator, which is based on the evidence presented in our Optimal Protein Intake Guide.

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Whey Protein has on your body, how much evidence there is, and how strong these effects are.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-b Minor Moderate See all 6 studies
Inclusion of dietary protein in the diet above the recommended daily intake appears to aid the process of fat loss during hypocaloric diets (eating less than required to sustain body weight). There is currently no demonstrated benefit with whey protein over other protein sources.
grade-b Minor Low See all 5 studies
Mixed effects on insulin, as there is an acute increase due to whey being a protein source (although whey increases insulin more than other proteins). Fasting insulin (chronically) tends to either be not affected or reduced, although the latter is usually confounded with weight loss.
grade-b Minor Moderate See all 4 studies
Protein in general increases lean mass, but there is not a significant body of evidence to support whey protein as being more effective than other protein sources
grade-b - High See all 3 studies
There doesn't seem to be an inherent effect of protein on power output, although it may augment training-induced power accural (an inherent effect of protein supplementation).
grade-b - Moderate See all 8 studies
The influence of whey protein on weight per se is highly unreliable, and is subject to the overall context of the diet. Protein in general can aid weight loss attempts and is required to build lean mass, with whey not having any demonstrated benefit over other protein sources.
grade-c Notable Very High See all 3 studies
Whey protein appears to increase muscle protein synthesis to a higher degree than other protein sources acutely, although over the prolonged supplementation it seems comparable in potency.
grade-c Minor Very High See 2 studies
Increased levels of glutathione are secondary to the Cysteine content and can be mimicked with all dietary sources of L-cysteine or supplemental N-acetylcysteine
grade-c Minor - See study
A decrease in Ghrelin has been observed with whey protein supplementation.
grade-c Minor Very High See all 3 studies
Has been noted to increase insulin sensitivity to a larger degree than casein when consumed by obese persons in a part of a fat loss diet; has not yet demonstrated an insulin sensitizing effect in lean athletes
grade-c Minor - See study
Possible LDL-C lowering effect, but has not yet been shown to be better than other protein sources.
grade-c Minor Very High See 2 studies
Possible reductions in triglycerides, but it is not sure if this is exclusive to whey protein or due to protein in general.
grade-c - - See study
Insufficient evidence to support a role of whey protein in improving blood flow
grade-c - Very High See 2 studies
Insufficient evidence to support the blood pressure reducing effects of whey protein
grade-c - Very High See all 5 studies
No significant influence on fasted blood glucose levels, may decrease postprandial glucose levels (relative to no protein ingestion) due to the release of insulin
grade-c - Very High See 2 studies
Currently no demonstrated benefit to bone mineral density, although protein in general appears to have a protective effect
grade-c - - See study
No demonstrated effects on C-Reactive Protein
grade-c - Moderate See 2 studies
No significant evidence to support an increase in HDL-C with whey protein
grade-c - - See study
Does not appear to inherently alter circulating IGF-1 levels
grade-c - - See study
Insufficient evidence to support whey protein as interacting with inflammation and biomarkers of inflammation
grade-c - Very High See 2 studies
No significant influence on circulating cholesterol has been demonstrated with whey protein
grade-d Minor - See study
Appears to reduce appetite (common to all protein sources), but its superiority over other protein sources is not yet demonstrated.
grade-d Minor - See study
Appears to decrease intestinal permeability, which is due to the glutamine content of whey protein.
grade-d Minor - See study
Has been associated with a decrease in liver enzymes (in steatohepatitis) but not to a remarkable degree; may simply be due to the L-cysteine content.
grade-d Minor Very High See 2 studies
Reductions in liver fat have been noted with whey protein supplementation, which is thought to be more effective than other protein sources due to the high L-cysteine content.

Studies Excluded from Consideration

  • Excluded due to being a mixture of whey, casein, and soy protein[5]

Frequently Asked Questions and Articles on Whey Protein

How can you assess protein quality?
Several scales have been developed to rate proteins according to their respective bioavailabilities and, more recently, amino acid profiles. Those scales can help guide your choice of protein, as long as you understand their premises and limitations.
Whey vs soy protein: which is better when losing weight?
Whey protein stimulates muscle protein synthesis rates more than soy protein, but supplementing with ~25 grams per day of either has similar effects on body composition over two weeks of dieting.
How much protein do you need after exercise?
A higher dosage of protein after your workout results in higher muscle protein synthesis (MPS).
Do muscle building supplements cause testicular cancer?
There is no evidence that muscle building supplements (MBS) can cause testicular cancer.
Does high-protein intake help when dieting?
We analyze a study which suggests that a higher protein-intake while dieting can help you lose more fat.
Whey Protein and Efficiency
Whey is a high-quality source of protein rich in the amino acid cysteine, which can bolster the body's antioxidant defenses, and glutamine, which can benefit intestinal health. There may also be an anti-cancer benefit with undenatured whey maintaining its bioactive peptide contents.
Fact check: does glutamine build muscle?
Glutamine supplementation does not affect body composition, but it may accelerate strength recovery from resistance-training sessions and reduce the occurrence of infections in hard-training endurance athletes.

Things to Note

Primary Function:

Also Known As

whey, whey concentrate, whey isolate, whey hydrolysate, hydrolyzed whey, whey protein powder

Do Not Confuse With

Milk protein, Casein protein

  • Whey protein is chemically non-stimulatory, but may provide energy via means of caloric consumption and an insulin spike from the amino acids.

  • Unflavored whey protein tends to be described as having a "brothy, diacetyl, sourness, and/or bitter"[1] taste, hence why Whey is routinely flavored as supplements.[2]

  • This bitter taste, especially that of the hydrolyzed whey (very bitter) can be somewhat negated by sucralose, fructose, sucrose, 5'AMP, 5'AMP disodium, sodium acetate and monosodium glutamate (MSG).[3] Table salt is partially effective, while the combination of cold water and a sour stimuli can suppress bitterness[4]

Click here to see all 288 references.