Whey, casein or plant protein: which to buy

Four things are on the shelf and the packaging works hard to make them sound more different than they are. Here is what actually separates them.

Whey concentrate, the sensible default

It scores at the top on the measures used to rank protein quality, it is the cheapest per gram of protein on almost every shelf, and it mixes without effort.¹

The case against it is narrow: it contains some lactose, and it is a dairy product. If neither of those applies to you, the reason to buy something else is preference rather than evidence.

Isolate, and what the extra money buys

Isolate is concentrate filtered further. More protein per scoop, less lactose, less fat.

That is a real difference on the label and a small one in outcomes. Nothing in the training research separates isolate from concentrate on muscle or strength; the analysis that established the intake ceiling worked in total protein, not in product type.²

Buy isolate if lactose is a problem, or if you are managing calories tightly enough that 20 kcal per serving matters. Otherwise the premium is buying purity you have no use for.

Casein, and the one thing it is for

Casein forms a gel in the stomach and releases amino acids over hours rather than in a rush. Whey is the opposite.

There is exactly one situation where that difference has an obvious application: a dose before sleep, where a slow release covers a long gap without food. Outside of that, the daily total is what matters and the speed of any single dose does not, which is the same conclusion protein timing reaches across the board.

The plant options

Soy is the strongest single plant protein: it is complete and scores closest to the dairy proteins.¹

Pea is good and short of methionine. Rice is short of lysine. Pea and rice are therefore sold blended, because each fixes the other's gap, and a blend behaves close to a complete source.

The honest summary of plant powders is that they land somewhat below whey on quality and the shortfall is a quantity adjustment rather than a barrier. If you are avoiding dairy, this is a solved problem and not a compromise worth agonising over. How protein quality is scored has the mechanics if you want to see where the gap comes from.

Collagen, which is a different thing

Collagen is sold beside these and does not belong in the comparison. It contains no tryptophan and is low in several other essential amino acids, so it cannot be used to build body protein the way the others can.

Whatever else collagen may or may not do, a 10 g scoop should not be counted as 10 g toward your daily protein. Plenty of people are unknowingly counting it, which is a quiet way to be 20 g short every day.

What actually decides this

The sports nutrition guidance sets its recommendation as a daily total, and the meta-analysis set its ceiling as a daily total.²³ Neither is stated per product, because the product is not the variable.

So the question underneath the shelf is a practical one: which of these will you actually drink, most days, for months? Taste and texture decide that, and they are not on any label.

Three things worth doing before committing to a large tub:

• Buy the smallest size first. Half of these are unpleasant to somebody, and the tub is not returnable once opened.
• Look for third-party testing. Supplements are regulated more lightly than food in most markets, so an independent certification mark is worth more than anything on the front.
• Compare on protein per 100 g, not per scoop. Scoop sizes differ and the per 100 g figure is the one that lets you price two products against each other.

Whether you need a powder at all is a separate question worth answering first. And if your protein intake is already managed as part of your medical care, which of these to use is a question for the clinician managing it rather than a preference: the comparison above is written for healthy adults.