What Is Whey Protein? WPC vs. WPI vs. WPH, Explained

Milk protein splits into two fractions: casein, which coagulates during cheesemaking and makes up most of milk's protein, and the remaining water-soluble whey. Whey protein powder is this soluble fraction, dried and processed — originally a cheesemaking byproduct. It's known for fast absorption and a relatively high leucine content among essential amino acids.

WPC (concentrate) undergoes the least filtering, landing at roughly 70–80% protein with some lactose and fat still present. WPI (isolate) is filtered further, reaching around 90% protein with most of the lactose and fat removed. WPH (hydrolysate) has been pre-broken into smaller peptides for faster digestion and absorption. That said, the 2019 meta-analysis pooling 8 RCTs compared each form against an isocaloric placebo rather than against each other, and lean-mass gains did not reach significance versus placebo for any form. Only one trial used WPH, and the authors state outright that a meta-analytic evaluation of hydrolysed whey was not possible. In other words, there is currently no basis for ranking the three forms.

~70–80%

Typical protein content (WPC)

~90%

Typical protein content (WPI)

Lactose intolerance stems from reduced activity of lactase, the enzyme that breaks down lactose. WPC retains more lactose, which can cause bloating or diarrhea in intolerant individuals; WPI has most of its lactose filtered out during processing, so it's less likely to trigger symptoms. That said, sensitivity varies a lot between people, and some still react even to WPI — start with a small amount if you're unsure. Note that milk allergy is a separate issue from lactose intolerance, and rules out whey-based products entirely.

Whey is commonly taken in 20–40 g servings. What matters more than serving size itself is whether your total daily protein lands around 1.6 g/kg body weight — a meta-analysis pooling 49 RCTs found gains plateau beyond that level. As for the claim that you must drink it within 30 minutes of training or lose the benefit, we've evaluated that separately in our piece on the "anabolic window" myth — worth a look if you're overthinking timing.

20–40 g

Typical serving size

~1.6 g/kg/day

Total intake where benefits plateau