What is whey protein? From production to performance

Whey protein is one of the most popular nutritional supplements in the world, particularly in the fitness industry. Its global market size was estimated to be $8.84 billion in 2024, which is projected to rise to $14.32 billion by 2030 (1). So, what is whey protein and what does it do?

More people are choosing whey protein because they’re learning about its health and performance benefits. It’s renowned for supporting muscle growth and recovery, but it also provides other benefits, including:

• maintaining muscle mass during a fat loss programme (2)
• suppressing appetite and increasing metabolism (3)
• reducing blood pressure (4) and unhealthy blood fats in overweight individuals (5)
• enhancing immune function and increasing the production of glutathione, the body’s master antioxidant (6)

Choosing the right whey protein supplement can be a challenge due to the wide variety available on the market. Products can differ in production, nutritional content, digestion rates, and the benefits they provide. Whey protein is made using cow’s milk, so even the cow’s diet will influence its precise nutritional content.

The situation becomes even more complicated because whey protein quality and effectiveness can vary widely between brands, no matter what the label claims. Some manufacturers use misleading—and sometimes almost deceptive—practices to make their products seem higher quality, more effective, or better value than they really are.

What is whey protein?

Whey is one of two primary milk proteins, the other being casein. It’s the liquid portion of milk that is separated from the curds during cheese production. The watery byproduct is processed to create whey protein powder.

Whey protein is a complete, high-quality protein that’s easy to digest and rich in both branched-chain amino acids and essential amino acids. These nutrients stimulate muscle protein synthesis more effectively than many other protein sources. It’s especially high in leucine, a key amino acid that triggers muscle growth and repair by signalling the body to shift from a catabolic state to an anabolic one.

Whey protein also contains important bioactive components—such as immunoglobulins, growth factors, and antioxidant peptides—that support immunity, growth, and overall metabolic health.

Because of these strong anabolic effects, the International Society of Sports Nutrition (ISSN) recommends whey protein as a highly effective supplement for improving muscle growth, recovery, and body composition when paired with resistance training.

Types of whey protein: concentrate vs isolate

The two most common types of whey protein are concentrate and isolate. Although they are both good sources of protein, the processing they undergo results in some key differences.

What is whey protein concentrate?

Whey concentrate is about 70–80% protein by weight and contains small amounts of fat, cholesterol, and lactose. It also retains more of its bioactive components and growth factors.

What is whey protein isolate?

Whey protein isolate is the product of a more intense processing phase than its concentrate counterpart. This removes virtually all the lactose and fat, which gives it a protein content of 90% or more by weight, resulting in a faster absorption rate. Another benefit is that it’s more suitable for people who are sensitive to lactose.

On the downside, whey isolate tends to be more expensive than concentrate, and although it has a higher protein content, it also has a reduced level of some of the immune-modulating and anabolic agents. Consequently, manufacturers often combine isolate and concentrate. This approach provides the benefits of both and is cheaper to produce than a pure isolate.

What is clear whey protein?

Clear whey protein is a hydrolysed whey protein isolate. This means that the whey has undergone a process known as enzymatic hydrolysis, where digestive-like enzymes break the protein into smaller fragments. Whey protein can be partially or fully hydrolysed. If a protein is partially hydrolysed, its amino acid chains are broken down into smaller segments. If it’s fully hydrolysed, they are broken down into individual amino acids.

Hydrolysed whey is usually 80–90% protein and offers several benefits. Because the body doesn’t need to break it down, it absorbs this protein faster than regular proteins, creating a quicker rise in blood amino acid levels. This rapid absorption is especially useful after workouts, when the body is primed to take in nutrients. It’s also easier to tolerate for people with digestive issues or food sensitivities.

Nature’s whey

In the last decade or so, undenatured whey protein (also known as native whey protein) has become commercially available. Most whey proteins come from cheese production, which uses high heat. In contrast, producers extract undenatured whey directly from raw milk using low-temperature microfiltration specifically for supplements. This makes it more expensive, but it usually contains around 90% protein, keeps all its amino acids intact, and has higher leucine levels. It sounds impressive—but is it actually better than regular whey?

A study by Hamarsland and colleagues (10) looked into this by comparing undenatured whey with regular whey and milk. They found that undenatured whey produced higher blood leucine levels than both regular whey and milk. Muscle protein synthesis also increased for 1–3 hours after exercise with regular whey, and for 1–5 hours with undenatured whey. Additionally, undenatured whey led to greater activation of p70S6K—a protein that promotes muscle growth—compared to milk at 180 minutes post-exercise.

It has benefits beyond muscle building too. Low-heat processing allows undenatured whey to retain more of its natural, bioactive components than regular whey.

The benefits of grass-fed dairy products

As the term suggests, grass-fed dairy products come from cows that are fed primarily on grass rather than a grain-based diet. This approach to feeding is not only better for the environment and associated with better animal welfare, but also increases the nutrient content of dairy-derived foods, including whey protein.

Grass-fed and grain-fed milk have the same amount of protein, carbohydrates, and calcium. But grass-fed milk has more nutrients that support health, such as omega-3 fats and conjugated linoleic acid (CLA). It also contains phytonutrients—plant compounds that act as antioxidants and help reduce inflammation and support the immune system. Because of these extra benefits and the higher cost of production, grass-fed whey is usually more expensive and sold as a premium product.

How to choose a good whey protein product

Understanding ‘what is whey protein’ and how it is made can help you choose a product that truly meets your needs. Whey protein can support your health and performance, but many brands use tricks to make their products seem better than they are. These may include:

• adding cheap amino acids to make the protein content look higher
• listing BCAAs in amounts too small to work
• hiding ingredient amounts in proprietary blends
• mixing in cheaper proteins like collagen
• rounding up protein numbers
• making claims—like “grass-fed”—that they cannot prove.

To avoid these problems, check the full amino acid profile, look for independent lab tests, and choose products that have third-party testing when possible. With a little research, you can find a whey protein that delivers what it promises and fits your goals and budget.

If you enjoyed this article and you want to learn more, why not take a look at our supplements for sport and exercise course. We also have a wide-range of specialist nutrition courses and qualifications available. These courses are primarily designed for fitness professionals.

References

1) Grand View Research. Whey Protein Market Size, Share, Trends | Global Industry Report, 2024 [cited 2025 Nov 2]. Grandviewresearch.com. 2015. Available from: https://www.grandviewresearch.com/industry-analysis/whey-protein-market

2) Frestedt JL, Zenk JL, Kuskowski MA, Ward LS, Bastian ED. A whey-protein supplement increases fat loss and spares lean muscle in obese subjects: a randomized human clinical study. Nutr Metab (Lond). 2008 Mar 27;5:8. doi: 10.1186/1743-7075-5-8. PMID: 18371214; PMCID: PMC2289832.

3) Johnston CS, Day CS, Swan PD. Postprandial thermogenesis is increased 100% on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet in healthy, young women. J Am Coll Nutr. 2002 Feb;21(1):55-61. doi: 10.1080/07315724.2002.10719194. PMID: 11838888.

4) Pal S, Ellis V. The chronic effects of whey proteins on blood pressure, vascular function, and inflammatory markers in overweight individuals. Obesity (Silver Spring). 2010 Jul;18(7):1354-9. doi: 10.1038/oby.2009.397. Epub 2009 Nov 5. PMID: 19893505.

5) Fluegel SM, Shultz TD, Powers JR, Clark S, Barbosa-Leiker C, Wright BR, et al. Whey beverages decrease blood pressure in prehypertensive and hypertensive young men and women. Int Dairy J. 2010;20(11):753–60. doi.org/10.1016/j.idairyj.2010.06.005

6) Kent KD, Harper WJ, Bomser JA. Effect of whey protein isolate on intracellular glutathione and oxidant-induced cell death in human prostate epithelial cells. Toxicol In Vitro. 2003 Feb;17(1):27-33. doi: 10.1016/s0887-2333(02)00119-4. PMID: 12537959.

7) Devries MC, Phillips SM. Supplemental protein in support of muscle mass and health: advantage whey. J Food Sci. 2015 Mar;80 Suppl 1:A8-A15. doi: 10.1111/1750-3841.12802. PMID: 25757896.

8) Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, Purpura M, Ziegenfuss TN, Ferrando AA, Arent SM, Smith-Ryan AE, Stout JR, Arciero PJ, Ormsbee MJ, Taylor LW, Wilborn CD, Kalman DS, Kreider RB, Willoughby DS, Hoffman JR, Krzykowski JL, Antonio J. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017 Jun 20;14:20. doi: 10.1186/s12970-017-0177-8. PMID: 28642676; PMCID: PMC5477153.

9) Patel S. Emerging trends in nutraceutical applications of whey protein and its derivatives. J Food Sci Technol. 2015 Nov;52(11):6847-58. doi: 10.1007/s13197-015-1894-0. Epub 2015 Jun 9. PMID: 26884639; PMCID: PMC4744604.

10) Hamarsland H, Nordengen AL, Nyvik Aas S, Holte K, Garthe I, Paulsen G, Cotter M, Børsheim E, Benestad HB, Raastad T. Native whey protein with high levels of leucine results in similar post-exercise muscular anabolic responses as regular whey protein: a randomized controlled trial. J Int Soc Sports Nutr. 2017 Nov 21;14:43. doi: 10.1186/s12970-017-0202-y. PMID: 29200982; PMCID: PMC5697397.

Author

Paul Orridge

Paul Orridge BSc (Hons)

Paul Orridge is a graduate in the field of sport, exercise and health, and has over 30 years’ experience within the fitness industry. In this time, he has performed a variety of roles including personal training, lecturing and writing. Paul now works as a freelance technical author and subject matter expert within the fitness industry. His work is based on his practical experience gained working with a diverse range of people from very unfit, overweight individuals to highly conditioned athletes, and is underpinned by the latest research.