Which protein should you buy, and when do you not need one at all?

40 bottles on the shelf and no real clue which one to pick

You walk into a supplement store or pull up a website and there they are: 40 bottles of protein. Whey, isolate, casein, plant-based, egg, rice, pea, collagen, BCAAs, and blends of all of the above, each one promising something a little different at a different price. You have no idea which one deserves your money, or whether any of them do.

You're not alone in that, because it's one of the most common questions among people who train. The supplement industry makes its money when you keep buying, not when you understand what you actually need. The published research finally brings some order to the mess. Researchers ran a Bayesian meta-analysis covering 75 clinical trials and 1,206 athletes. A separate controlled clinical trial put plant protein head to head with whey. And a network meta-analysis pooled 78 studies and 4,755 participants to compare 13 different types of protein.

This article turns those numbers into actual purchasing decisions. The goal isn't to sell you a bottle. It's to help you work out whether you need one at all, which to choose if you do, and when your money buys more at the grocery store than it does at the supplement store.

Before buying: do you really need protein powder?

Nobody in the store is going to ask you this one. It's the most important question of all.

Protein powder is a supplement, which means its job is to complete something you're missing rather than replace your diet. If you already eat enough protein across the day from chicken, fish, eggs, legumes, dairy, or tofu, you may not need to spend a single euro on powder.

The evidence is consistent on one point the industry would rather not put in bold: what matters most for building muscle and improving performance is the total protein you take in over a day. Not where it comes from, not whether it arrives as powder or on a plate, not whether the packaging looks good or an influencer swears by it. The total daily dose.

So when does buying a bottle actually make sense? When your daily routine leaves no room to cook enough, when you need something fast and practical after training because your schedule won't let you sit down to a meal, when you travel constantly and can't hit your target on food alone, or when you're vegan and need to round out the amino acid profile of your diet. In those situations a tub of protein is a practical and inexpensive tool. A tool, though, not a magic wand. If you're counting on a bottle to do the work your diet, your training, or your sleep isn't doing, you're going to be disappointed.

What 75 clinical trials say about protein supplements and performance

In 2025, a multilevel Bayesian meta-analysis published in the Journal of the International Society of Sports Nutrition pooled 75 randomized clinical trials and 1,206 athletes, to measure how protein supplementation affects sports performance and recovery after exercise.

Overall, supplemented protein had a positive effect on muscle strength, with a Bayesian effect size of 0.72 and a 95% credible interval of 0.18 to 1.27, and on resistance performance, at 0.37 with an interval of 0.02 to 0.71, and both of those results are statistically significant. The picture for post-exercise recovery is weaker: the effects on glycogen resynthesis and on fatigue reduction fell short of significance in the overall analysis, although they did turn up in specific comparisons.

There's one finding buried inside this study that changes the whole conversation, and we'll come back to it. For now, what matters is that protein supplementation can help, that the effect size is modest, and that it depends heavily on the conditions.

Whey: why it still has the most backing

Of the 13 types of protein analyzed across these studies, whey, the milk protein left over from cheesemaking, carries the most evidence behind it. The Bayesian meta-analysis does not break its results down by source, it measures supplemental protein as one block, so no number in it speaks about whey alone. The one that compares the sources against each other is the network meta-analysis.

That network, covering 78 studies and 4,755 healthy adults doing strength training, is what puts whey where it is: whey is one of only two proteins that beat placebo on both strength gain and lean mass by a statistically meaningful margin. Its effect size for strength was 0.15, interval 0.03 to 0.27, which works out to roughly 2.2 extra kilos of strength on average.

Why does whey work? There's nothing magic about it: it's the most studied source, it absorbs quickly, and it has a very complete amino acid profile with a high concentration of leucine, the amino acid that does the most to switch on muscle protein synthesis. Choosing whey means choosing the option with the most research miles on it, which is not at all the same thing as the only valid option.

If you have no dietary restrictions to work around, no lactose intolerance and no vegan diet, and you want the safest bet available, a basic tub of whey concentrate or whey isolate is the option with the most data behind it. Skip the premium version with 14 extra ingredients, because a simple whey with a short ingredient list does the job just as well.

Plant protein versus whey: what a trial with 44 people says

A debate that keeps resurfacing in sports nutrition is whether plant proteins can match whey for building muscle. Santini and colleagues at the University of São Paulo tested exactly that in a clinical trial, also published in the JISSN, in 2025.

The researchers recruited 44 young untrained men and randomly assigned them to two groups, one taking 45 grams of whey protein a day and the other 45 grams of a soy and pea blend, with both groups following the identical supervised strength training program for 12 weeks, 3 times per week.

The results were unambiguous: no significant differences between the groups on any variable measured. The plant protein group gained an average of 2.4 kilos of total lean mass and the whey group 2.5 kilos, a gap that was not statistically significant, with every P value for the between-group comparison above 0.05. Lower-body strength told the same story, with the plant group improving 64 kilos on the leg press and the whey group 63 kilos. Even the cross-sectional area of the vastus lateralis, a direct tissue-level measure of hypertrophy, came out comparable. The plant group added 0.9 cm² and the whey group 1.3 cm², with no significant difference between them.

None of this means every plant protein equals whey in every circumstance. It means a well-formulated plant blend, with soy and pea combined to complete the amino acid profile, can deliver equivalent results when the dose is right and the training is the same, so if you're vegan, lactose intolerant, or simply partial to plant protein for any reason at all, the data from this trial says you aren't sacrificing results.

Dose and the combination of sources are what matter here. Plant proteins tend to run slightly lower in leucine than whey, so you may need a bit more of them to get the same protein synthesis stimulus, and in this study 45 grams a day split into three 15-gram servings at breakfast, lunch, and dinner erased the practical difference completely. If you go plant, look for blends that combine at least two sources, soy with pea or pea with rice, so that you cover all the essential amino acids.

Casein, milk protein, and others: why they don't stand out in the data

If whey is the star, what about the other types of protein filling the shelves?

The Bayesian meta-analysis of 75 trials doesn't publish a separate result for each source, and the analysis that does compare them one by one is blunt: apart from collagen and whey, no supplement separated itself from placebo. That doesn't automatically mean they don't work: there may be too few studies to detect an effect, the effect may be smaller than statistical significance requires, or they may genuinely offer no measurable benefit over placebo under the conditions studied.

In the network meta-analysis of 78 studies, casein didn't separate itself from placebo for either strength or lean mass, and milk protein didn't either. It isn't that either one is harmful; it's that the available data gives them no clear advantage over not supplementing at all.

That has a direct practical consequence: if someone sells you casein as the slow-absorbing nighttime protein that will build muscle while you sleep, ask them where the data supporting that claim is. In the two big reviews covered here, casein shows no superiority, and while it can certainly work as a protein source, since it does contain amino acids, it doesn't have the backing that whey has.

Collagen: a surprise that still isn't clear

This one calls for extra care. The network meta-analysis says something nobody expected.

In the network meta-analysis of 78 studies and 4,755 participants, collagen ranked first for lean mass, with a large effect size of 0.94, and first for strength as well, at 0.41, which puts it ahead of whey.

Before you go out and buy a tub of collagen, several things should give you pause. The number of collagen studies inside that network is small next to the number for whey, and when studies are few the results get unstable and can be inflated by one or two trials with small samples or favorable designs. The Bayesian meta-analysis of 75 trials classified collagen as insufficient data for drawing any conclusions. And collagen's amino acid profile is known to be incomplete for muscle protein synthesis, since it lacks leucine in meaningful amounts, and leucine is the amino acid that switches on the muscle-building machinery.

So what do you do with this? Be honest about what we know and what we don't. Collagen may well have real benefits for joints, tendons, and connective tissue, and it's possible it affects lean mass through mechanisms we don't yet fully understand, mechanisms other than direct protein synthesis. But recommending collagen as your primary protein for building muscle on the strength of one ranking in one study would be premature, because the evidence isn't solid enough for that yet.

If you already take collagen for your joints or your skin and it agrees with you, carry on. As your main protein supplement for strength training, though, whey or a good plant blend still rest on far more robust backing.

Loose BCAAs: why you probably don't need them

BCAAs, the branched-chain amino acids leucine, isoleucine, and valine, had their run as the star supplement, sold in expensive tubs that promised better recovery, less fatigue, and more muscle growth. Plenty of supplement stores still give them premium shelf space, at prices that are anything but cheap.

Neither of the two major reviews found significant evidence for BCAAs as a standalone supplement, and the explanation for that is simple. If you already take in enough complete protein, whether from food, from whey, or from a plant blend, the BCAAs you need are already in it. A 25-gram scoop of whey carries roughly 5 to 6 grams of BCAAs naturally, and so does a 150-gram chicken breast. Adding loose BCAAs on top of that is like pouring water into a pool that's already full, and the excess adds nothing you can measure.

Is there any case where loose BCAAs make sense? Possibly, if you train in a prolonged fasted state and can't eat anything for hours before or after your session, but that scenario is extremely specific, and if you train under normal conditions it isn't yours. If you eat breakfast, eat after training, and take in enough protein across the day, loose BCAAs are money wasted, and that money does more good spent on real food or on a complete protein that already contains them. In that same aisle there is another capsule that does survive a critical read: Omega-3: a supplement supported by evidence or marketing that smells fishy.

Total dose matters more than bottle type

If you take one idea away from this entire article, make it this one: the total amount of protein you eat each day matters far more than which type of supplement you buy.

The Bayesian meta-analysis of 75 trials found that total daily protein dose is the single strongest predictor of results. A total intake of roughly 2 grams of protein per kilo of body weight per day showed the strongest association with performance improvements. The authors put a number on it: adding around 1 gram per kilo per day from a supplement, until you hit that total, is what works best.

What does that look like in practice? If you weigh 75 kilos, your target sits somewhere around 150 grams of protein a day, food and supplements combined. Hit that number on real food alone and a tub of protein adds no meaningful benefit; come up 30 or 40 grams short and a shake is a practical way to close the gap.

Spending 50 euros on a premium tub isn't worth it if you then fail to eat enough protein the rest of the day, while a basic 20-euro whey or a plant blend with a good ingredient profile can give you exactly what you need. The tub isn't the star of the show; it's the supporting actor that rounds out the cast.

The finding that changes the conversation: when calories are equal, the difference disappears

Now for the data the supplement industry would rather you skipped.

The Bayesian meta-analysis did something a lot of earlier work skipped over. It separated the studies in which the protein group and the control group consumed the same total calories, the energy-matched studies, from the studies in which the protein group picked up extra calories simply by taking the supplement, the non-matched ones.

The result was revealing: when calories were matched between groups, the effects of protein supplementation on resistance performance, on muscle strength, and on recovery all stopped being significant. When calories were not matched, meaning the protein group ate more total calories, the effects were significant, and the authors themselves conclude that the observed benefit may not come down to the protein itself.

What does that tell us? That a good share of the benefit credited to protein supplements may come from eating more calories overall rather than from anything special in the powder itself. If your diet already covers your calorie and protein needs, adding a shake on top may deliver no extra measurable benefit, because the supplement earns its keep when it fills a real gap in your diet, not when it piles onto a diet that was already sufficient.

None of this invalidates protein supplementation, and if a shake is what gets you to your daily protein target in a practical way, it's still useful. But it should make you think twice before you credit your results to the tub, when the real cause may be that you finally ate enough.

How long you need to supplement to see results

The Bayesian meta-analysis also looked at how long supplementation runs, and found that the range for seeing effects on sports performance falls between 40 and 65 days, stretching out to 80 days for post-exercise recovery.

That carries two practical implications. The first: if you buy a tub, take it for two weeks, and notice no difference, that isn't evidence it doesn't work. Effects need at least 6 to 9 weeks to become measurable, and changes in body composition and strength take time, so quitting after two weeks because you feel nothing means never giving it a chance. The second: you don't need to supplement for years on end without a break. The data suggests the benefit peaks somewhere around 8 to 10 weeks and then levels off.

A reasonable approach looks like this. If you decide to supplement, give it at least two months before you judge whether it works for you, and measure something concrete along the way. Are you hitting your daily protein target consistently? Has your recovery between sessions improved? Is your strength moving week to week? Once that period is over, if your overall diet has improved and you no longer need the tub to hit your target, drop it without a second thought, because supplementation is not a lifetime contract, it's a tool you pick up when you need it and put away when you don't.

Smart buying guide: what to look for, what to avoid, and how not to waste money

Say you've read all of that and concluded a tub of protein does make sense for your situation. Here's what to look for and what to steer clear of.

Start with the ingredient list rather than the front of the tub. The first ingredient should be the protein source itself: whey concentrate, whey isolate, soy protein, a pea and rice blend. If the first ingredient is maltodextrin, sugar, or filler of any kind, the tub holds more filler than protein. Look for a short ingredient list, the protein source, maybe an emulsifier such as soy or sunflower lecithin, and a flavoring, because you really don't need much more than that.

Check how many grams of protein each serving actually delivers, since a good tub should give you at least 20 to 25 grams per serving, usually one scoop. If a 30-gram serving of powder contains only 15 grams of protein, you're paying for a lot of filler.

Always compare price per gram of protein, never price per kilo of powder. A 1-kilo tub at 25 euros that's 80% protein gives you 800 grams of actual protein for 25 euros, or 0.031 euros per gram, while a 2-kilo tub at 60 euros that's 60% protein gives you 1,200 grams of protein for 60 euros, or 0.05 euros per gram. The bigger tub costs more per gram even though it looks like the better deal per kilo.

Steer clear of exclusive formulas, proprietary amino acid matrices, and any claim that sounds like marketing with no data underneath it. A tub that promises miraculous results is selling you marketing, not science. The Bayesian meta-analysis concludes that the effect of protein supplementation is limited, so any product promising more than that is lying to you.

And before you spend anything on powder, do the arithmetic. How much protein are you already eating each day from real food, and how far short does that leave you? If the gap is small, say 10 or 15 grams, then one more egg, a Greek yogurt, or 100 grams of chicken solves it without your opening your wallet. A tub earns its place when the gap between what you eat and what you need is large and your schedule won't let you close it with food alone.

Your training deserves good fuel, but the bottle is not the first priority

If you've read this far, the conclusion should be clear enough: protein supplementation can help, its effect is more modest than the industry lets on, it depends enormously on your overall diet, and the type of protein matters less than your total daily dose.

Whey is the option with the most science behind it, and well-formulated plant blends of soy and pea can deliver equivalent results when the dose is right. Casein and milk protein don't stand out in this evidence. Loose BCAAs are unnecessary once you're already eating enough complete protein. And collagen, surprising results in a single analysis notwithstanding, needs more research before anyone can recommend it as your main protein for building muscle.

One thing is worth holding onto before we wrap up. When studies matched calories between the supplementing group and the non-supplementing group, the differences disappeared, which means part of what we credit to the supplement may simply be the effect of eating enough. Before you spend on powder, get your overall diet in order, because a tub of protein doesn't compensate for a poor diet or for insufficient rest.

Work out the number you actually need before you buy any tub: How much protein you really need (and how to get there without tubs or strange powders).

Your training at Gym Triple X deserves good fuel. But the best investment isn't always the most expensive tub on the shelf. Sometimes it's a well-stocked refrigerator, a meal plan that lets you hit your daily protein target consistently, and a basic whey or plant blend that covers what's missing on the days life won't let you cook. That's smart supplementation, and everything else is marketing.

Before you close the tab, a thought. If while reading this you kept feeling you lack context about your own body, a personal trainer on the Costa del Sol is there for precisely that. No commitment, and no pressure to decide anything today.