What is whey protein?
Whey is the liquid byproduct of cheese and yoghurt production. It contains all nine essential amino acids, making it a complete protein. It exists in two primary supplemental forms: whey protein concentrate (WPC), which retains more fat and lactose at 70–80% protein by weight, and whey protein isolate (WPI), which is further processed to 90%+ protein with minimal fat and lactose.
How it works
Whey is rapidly digested and absorbed, producing a fast, high peak in plasma amino acid levels — particularly leucine, which directly activates the mTOR pathway responsible for initiating muscle protein synthesis. A single serve of whey delivers sufficient leucine (typically 2.5–3g) to maximally stimulate muscle protein synthesis, making it the most efficient protein supplement available.
What the research says
- Whey protein supplementation combined with resistance training produces significantly greater lean mass gains than training alone (Tang et al., 2009)
- WPI produces a faster, higher leucine peak than WPC, but both stimulate muscle protein synthesis equally when matched for leucine content
- Post-exercise whey supplementation reduces muscle damage markers and accelerates recovery
- No significant benefit to consuming whey within a specific "anabolic window" — total daily protein intake matters more than timing
Effective dose
25–40g per serve, providing approximately 2.5–3g of leucine. For most people targeting 1.6–2.2g of protein per kg bodyweight, 1–2 serves of whey protein per day fills dietary gaps efficiently. More than 40g in a single serve does not appear to stimulate greater muscle protein synthesis acutely.
What to check on the label
Check protein percentage per serve — divide protein grams by total serve weight. WPI should be 85%+ protein per gram of powder; WPC 70–80%. Avoid products with significant added sugars, fillers, or thickeners that inflate the total serve weight without adding protein. Third-party testing for amino spiking is worth looking for in budget products.
Safety
Safe for healthy adults with normal kidney function. The concern about high protein intake damaging kidneys is not supported by evidence in people without pre-existing kidney disease. Those with lactose intolerance typically tolerate WPI better than WPC due to lower lactose content.