What Is Whey Protein? A Complete Guide

Whey protein is the most popular sports supplement in the world, but many people use it without really understanding what it is. Here is a straightforward, science-backed guide.

What Is Whey?

Whey is one of the two proteins found in cow's milk (the other is casein). When milk is processed to make cheese or yogurt, the liquid that separates from the curds is whey. This liquid is then filtered, dried, and turned into powder.

Milk protein is roughly 80% casein and 20% whey. Despite being the smaller fraction, whey has become the supplement of choice because it is rapidly digested and exceptionally rich in essential amino acids.

Types of Whey Protein

Whey Concentrate

• Protein content: 70–80% by weight
• Contains: Some lactose, fat, and minerals
• Taste: Generally the best flavour and creamiest texture
• Cost: Least expensive
• Best for: Most people who tolerate dairy well

Whey Isolate

• Protein content: 90%+ by weight
• Contains: Very little lactose and fat (typically <1%)
• Taste: Thinner, lighter texture
• Cost: Mid-range
• Best for: People with mild lactose sensitivity, or those who want maximum protein per calorie

Whey Hydrolysate

• Protein content: 80–90% by weight
• Contains: Pre-digested (broken into smaller peptides)
• Taste: Often bitter; usually heavily flavoured
• Cost: Most expensive
• Best for: Rarely necessary - the absorption speed advantage over isolate is minimal for most people

For the vast majority of users, concentrate or isolate is the right choice. Hydrolysate is not worth the price premium unless you have very specific digestive issues.

Why Is Whey Protein So Effective?

Whey protein has three key advantages:

1. Rapid Digestion

Whey is absorbed faster than any other common protein source. Amino acids appear in the bloodstream within 20–30 minutes and peak around 60–90 minutes (Boirie et al., 1997, PNAS). This makes it ideal for post-workout recovery.

2. High Leucine Content

Leucine is the amino acid that triggers muscle protein synthesis (MPS). Whey contains approximately 10–12% leucine by weight - more than any whole food or other protein powder. A single 25g scoop of whey provides about 2.5–3g of leucine, which crosses the threshold needed to maximally stimulate MPS (Churchward-Venne et al., 2012).

3. Complete Amino Acid Profile

Whey scores a perfect 1.0 on the PDCAAS scale, meaning it provides all nine essential amino acids in optimal ratios. It also scores among the highest on the newer DIAAS (Digestible Indispensable Amino Acid Score) metric.

What Does the Research Say?

The International Society of Sports Nutrition (ISSN) position stand on protein and exercise concludes that whey protein supplementation, combined with resistance training, effectively increases lean body mass and strength (Jäger et al., 2017, JISSN).

A meta-analysis of 49 studies found that protein supplementation significantly enhances muscle mass gains during resistance training, with whey being the most commonly studied and validated source (Morton et al., 2018, British Journal of Sports Medicine).

Who Should Use Whey Protein?

Whey is beneficial if you:

• Struggle to hit your daily protein target through food alone
• Want a convenient post-workout option - faster than cooking a meal
• Are trying to build muscle and want to ensure adequate leucine intake
• Are in a calorie deficit - whey isolate provides high protein with minimal extra calories

Whey is not necessary if you already meet your protein goals through food. It is a supplement, not a requirement.

How to Use Whey Protein

• Standard serving: 25–30g (one scoop) mixed with water or milk
• Post-workout: Within a few hours of training
• In recipes: Add to oatmeal, smoothies, pancakes, or baked goods
• With coffee: Mix into your morning coffee for a protein-boosted drink

Track your shakes alongside your meals in Protein Pal to see how they fit your daily total.

The Bottom Line

Whey protein is a fast-digesting, leucine-rich, complete protein derived from milk. Concentrate and isolate are the two forms worth considering for most people. It is the most well-researched protein supplement available and is effective for supporting muscle growth and meeting your daily protein needs.

For a comparison of whey against casein and plant-based options, see our protein powder comparison guide.