What is whey protein, and do you need it?

Where whey comes from

Cheese starts with milk and something to make it curdle, usually an enzyme or an acid. The milk separates into solid curds, which become the cheese, and a thin, cloudy liquid, which is the whey. You’ve probably seen it without knowing the name: the watery layer that collects on top of a pot of yogurt is whey too.

About 80 percent of the protein in milk is casein, and it ends up in the curds. The other 20 percent stays dissolved in the whey. Fresh whey is still mostly water, though, along with milk sugar (lactose), a little fat and some minerals, so the protein has to be separated out. The liquid is pasteurized and pushed through very fine filters that keep the protein and let most of the water, lactose and fat go, and what remains is dried into a powder. Flavoring and a sweetener usually go in at the end.

Nothing in that process creates protein. It’s the same whey protein that was in the milk, with most of the rest of the milk taken away, and a lot of milk goes into one tub. A glass of milk (240 ml, a cup) has about 8 grams of protein, and only a fifth of that is whey. A single scoop of powder holds about 24 grams, which is the whey protein from somewhere around fifteen glasses.

What whey protein does in your body

Your body handles whey the way it handles the protein in an egg or a chicken breast. It breaks the protein down into amino acids and uses them to build and repair tissue, muscle included.

Two things set whey apart from most protein foods. It digests quickly, and it’s rich in leucine, the amino acid that does the most to switch muscle building on. That is where whey’s reputation comes from. Lab studies that track muscle building for a few hours after a shake often put whey ahead of other proteins.

Over weeks and months, which is where it counts, most of that lead disappears. Across 49 trials of people lifting weights, a protein supplement did help. The people who took one gained about 0.3 kg (two thirds of a pound) more lean mass than the people who only trained, and beginners and older lifters gained less than that. But the supplement stopped adding anything once people were eating about 1.6 grams of protein per kilo of body weight a day in total. What kind of protein they took, or when they took it, made little or no difference.

So whey protein works, and it works because it’s protein. A shake adds a little to what training builds. It doesn’t replace the training, and it doesn’t do anything that the same amount of protein from dinner wouldn’t do. What matters is how much protein you eat in a day, which is the subject of our article on how much protein you need.

Is whey protein good for you?

For a healthy adult, yes, in the same way milk or eggs are good for you. One of the first things we teach clients at Gains For Gamers is that there are no healthy or unhealthy foods viewed in isolation: it’s all about how often, and how much, you eat of something. Whey powder is a food, so the same goes for it. A scoop a day alongside normal meals is one thing. Four scoops a day standing in for those meals is another.

A few groups do need to think before they buy a tub:

• If you have kidney disease, how much protein you eat is your doctor’s call, and powder counts. In healthy adults the worry doesn’t hold up: across the trials, kidney function followed the same path on higher-protein diets as on normal ones.

• If lactose gives you trouble, check which kind of whey you’re buying. A scoop of whey concentrate carries roughly 3 to 8 grams of lactose, less than the 12 or so in a glass of milk, and most people with lactose intolerance tolerate 12 to 15 grams at a time well. A whey isolate has less than a gram.

• If you have a milk allergy, whey is out, isolate included. A milk allergy is a reaction to the milk proteins themselves, and whey is one of them.

• If you’re pregnant, breastfeeding or under 18, ask your doctor or midwife before you add any supplement, this one included.

What else is in the tub

The more reasonable worry about protein powder isn’t the whey. It’s whatever else came along with it, and the headlines have been about heavy metals, lead above all. Nobody checks a supplement before it goes on sale, at least not in the US, so most of what we know comes from consumer groups buying tubs and testing them.

The best known test is from Consumer Reports, a US consumer organization. In 2025 it tested 23 protein powders and ready-made shakes, and in more than two thirds of them a single serving had more lead than its experts say is safe to have in a whole day.

Two things put that result in proportion. The first is how strict the limit is. Consumer Reports uses half a microgram of lead a day, the level at which California requires a warning label, and it says itself that its results show which products have more lead than others, not the point where harm begins. For comparison, the FDA’s benchmark for lead from all food is 8.8 micrograms a day. That benchmark is set for women who could become pregnant, and it has a tenfold safety margin built in.

The second is where the lead was. Plant-based powders had about nine times as much as dairy-based ones on average. The ordinary dairy-based powders in the test, two of them plain whey, came in under even Consumer Reports’ limit, at about a third to a half of it. The dairy-based products that went over were ready-made shakes and one mass gainer, at about 1 microgram a serving or less.

What a test finds in a tub and what that amount does to a person are two separate questions. Toxicologists have worked through the results of two earlier rounds of testing to answer the second one. For every product but one, the metals stayed under recognized health limits even at three servings a day, and the lead from a powder was small next to what people already take in from everything else. Plain whey powders came out lowest. The “mass gainer” products came out highest.

No amount of lead has been shown to be safe, so less is better, and that is worth a minute of your attention when you choose a powder. It’s a good reason to pick a whey that has been independently tested, and not to live on shakes. It isn’t a reason to be afraid of the tub.

Do you need it?

Need it, no. There is nothing in a tub of whey that you can’t get from food, and if your meals already bring you to the protein you need in a day, a shake adds nothing.

So the first question isn’t about powder at all. It’s whether you get enough protein from what you already eat, and if you’ve never added it up, you may not know. Our protein calculator works out your daily target, and adding up a normal day or two of your meals shows you how close you are.

If you come up short, this is where a tub earns its place. Say your target is 130 grams and a normal day of your meals comes to about 100. You could close that gap with food, with a bigger piece of chicken at dinner and a pot of yogurt in the afternoon. But that means planning, buying and eating another portion, every day. A scoop of whey in water is about 24 grams of protein. It takes a minute, it needs no fridge and no cooking, and the tub keeps for months in a cupboard.

How much a shake does for you depends on what you already eat and how much you need. If you’re 30 grams short, one shake covers most of the gap. If you’re 60 short, it covers less than half, and the rest still has to come from your meals. If you’re already there, it covers nothing.

A shake also gets you that protein for very few calories, which comes straight from how the powder is made: most of the milk has been taken away.

Food can do that trick too. A small can of light tuna gives you about 20 grams of protein for about 100 calories, and there are more foods like it in our list of high-protein snacks. But a can of tuna isn’t always what you want at 7 in the morning, or in the car.

The powder doesn’t have to be a shake, either. People stir a scoop into a bowl of oats or a pot of yogurt, or mix it into pancake batter. A bowl of oats has about 10 grams of protein by itself, and with a scoop stirred in it has over 30. That doesn’t make the oats or the pancakes any healthier. It makes them higher in protein, which is the only job the powder has.

Then there is the price, which looks worse on the shelf than it is. A big tub costs a lot in one go, but what matters is what you pay for the protein in it, and that is easy to work out: divide the price of the tub by the number of servings. At US prices in the summer of 2026, a scoop from a large tub came to roughly a dollar, with the cheapest tubs nearer 60 cents and the best-known brands above $1.30. The same 25 grams of protein from chicken breast cost about a dollar, from eggs about 75 cents and from ground beef about two dollars.

So whey isn’t the cheapest protein you can buy, and it has become a good deal more expensive in the last few years. But it costs about the same as the foods people think of as cheap protein. Prices differ a lot from country to country and shop to shop, so do the division with the tub in front of you.

Put together, a tub is worth buying when one of these is true:

• Your days are irregular, and a proper meal with protein in it often doesn’t happen.

• You know how much protein you need, and your meals keep leaving you 20 or 30 grams short.

• You’re trying to lose weight, and you want protein that doesn’t bring many calories with it.

What a tub isn’t good for is replacing meals, and the reason is the same one that makes it useful. A shake is milk with almost everything except the protein taken out. That is what makes it handy, and it’s also what makes it a poor meal, because it has no fiber and little of what else a plate of food gives you. It tops up a day of meals well. It replaces them badly.

How to choose one without being sold to

If you do buy one, three things on the tub are worth checking, and most of the rest is marketing.

How much of the scoop is protein. Divide the protein in a serving by the size of the serving. About 24 grams of protein from a 30 gram scoop is 80 percent, which is what a plain whey powder looks like. If a 50 gram scoop gives you 20 grams of protein, more than half of it is something else, usually carbohydrate. At the far end are the mass gainers, which are mostly carbohydrate with some protein added. They have also tended to come out worst in the heavy metal tests, which is less surprising when one serving is several scoops.

Whether anyone independent has tested it. Look for a third-party certification mark on the tub, and check what that mark covers. NSF Certified for Sport, for one, checks that what’s in the tub matches the label and that contaminants are under its limits. Some other marks only test for substances banned in sport, which matters to a drug-tested athlete and tells you nothing about lead.

Whether you’ll keep drinking it. A tub you don’t like the taste of ends up at the back of a cupboard. Buy the smallest size of a new flavor first.

The kind of whey matters less than the label makes it look:

The three kinds of whey powder

The same goes for the extras. Added amino acids (often listed as BCAAs) are already in whey, which is about 11 percent leucine as it is. And a promise built on timing, like a “post-workout” formula, is selling you something the training studies couldn’t find: when people took their protein made little or no difference.

If you don’t eat dairy, a plant powder does the job. Soy is the best studied: across 17 trials, soy protein and milk protein built the same amount of muscle. For other plant proteins, such as rice and oat, the trials are few, and milk protein came out somewhat ahead in them. Since plant powders were also the ones with the most lead in Consumer Reports’ test, independent testing matters even more there.