Whey Concentrate vs Isolate vs Casein: What's the Difference?

The short version

Whey and casein are the two proteins in milk. Whey is the liquid part that separates when milk is made into cheese; casein is the part that curdles. How the whey is processed after that decides whether you end up with concentrate or isolate.

Whey concentrate

Concentrate is whey that has been filtered just enough to raise its protein content. It keeps a little more of the milk's natural fat and lactose than isolate, often tastes slightly creamier, and is usually the cheaper option. For most people it is a perfectly sensible default.

Whey isolate

Isolate is filtered further to remove more of the fat and lactose, so a serving has more protein and fewer carbohydrates. As a real example, the UK/EU label for Optimum Nutrition Gold Standard 100% Isolate (chocolate) lists 25 g of protein, 1.3 g of carbohydrate (of which 0.3 g sugars) and 110 kcal in a 30 g serving, which is 83 g of protein per 100 g. Because isolate contains less lactose, some people who find ordinary whey hard to digest prefer it. It is not lactose-free, though, so check the label if that matters to you.

Casein

Casein is the other main milk protein. It digests more slowly than whey, which is why it is often taken in the evening or between meals, as with Optimum Nutrition's Gold Standard 100% Casein. For building muscle over weeks and months, though, your total protein across the day matters far more than which type you use. If you're not sure how much that is, use our protein calculator or read how much protein you actually need.

Which should you buy?

Start with concentrate if you want the best value. Choose isolate if you want fewer carbohydrates and less fat per scoop, or you find regular whey heavy. Choose casein if you want a slower-digesting protein for the evening. Whichever you pick, the best protein is the one you will actually take every day.

Compare products per serving, not per tub: look at the grams of protein in one serving and the size of that serving, because a tub with bigger scoops is not necessarily better value. Our guide to reading a supplement label shows how.

If you avoid dairy, plant protein powders exist too (usually blends of pea, rice or soy). Check the protein per serving on the label, as it varies between products.