Heavy Metals in Protein Powder: What the Testing Found

Heavy metals in protein powder stopped being a theoretical worry in January 2025. That month the Clean Label Project published results from testing 160 powders, covering most of what Americans actually buy, with an independent lab running them for arsenic, cadmium, lead and mercury.

Nearly half exceeded California’s Proposition 65 limits. About a fifth came in at more than twice those limits.

Then two findings that run against everything the category’s marketing tells you. Plant-based powders carried three times the lead and five times the cadmium of whey. And organic products tested worse than conventional: three times the lead, twice the cadmium.

Chocolate was the worst of all. Four times the lead of vanilla, and up to 110 times the cadmium.

The counterintuitive results make sense

None of this means organic is a scam or that plants are bad for you. The explanation is duller and more useful than that.

Heavy metals in food mostly come from soil. Plants pull them up through their roots along with everything else, so anything built from concentrated plant material concentrates whatever was in the ground it grew in. Whey starts from milk, which passes through a cow first, and that filters a lot out.

Cacao is the extreme case. Cocoa plants take up cadmium readily, above all in parts of South America where soil levels are naturally high, which is why chocolate protein powder and dark chocolate keep turning up in this kind of testing. It isn’t an additive. It’s the crop.

Organic follows from the same logic. Organic certification governs what gets sprayed on a crop, not what was already in the dirt. A field can be free of synthetic pesticides and still sit on soil with a century of industrial deposition in it. Organic and low-metal are simply different questions, and buying the first does not answer the second.

The part the industry disputes, fairly

I’m not going to present this as settled, because it isn’t, and the pushback has a real point in it.

Proposition 65 is a California labeling law, not a safety threshold. It triggers a warning notice, and its limits are set far below federal ones deliberately. The Council for Responsible Nutrition argued that reporting “exceeds Prop 65” as though it meant “unsafe” strips out that context, and asked Clean Label Project to put the work through peer review. That’s a reasonable ask, and the report hasn’t been through it.

So “47% exceeded Prop 65” does not mean 47% of protein powders will hurt you. It means 47% carried enough of these metals that California would want a label on them.

What it does tell you is a comparative story, and that part survives the criticism intact. The same lab ran the same test on every sample. Some powders came back with many times the lead of others. That gap is real regardless of where you think the safety line sits, and it’s the gap you can actually act on.

Concentration is what changes the maths

Two things make protein powder different from eating a plant.

It’s concentrated. Turning peas into pea protein isolate removes water, fiber and starch and keeps the protein, and anything bound up in that material comes along for the ride at a higher density than the original crop.

And it’s daily. Most people using protein powder use it every day, often for years, in scoops rather than sprinkles. These metals matter mostly through cumulative exposure rather than single doses, so a daily habit is exactly the pattern where a small difference between products adds up.

That combination is the argument for caring here specifically, rather than treating it as one more thing to worry about at the supermarket.

What I’d actually do

Whey, if it suits you. On this specific issue whey has the better numbers by a wide margin, and that’s the single biggest lever available.

Skip chocolate, or accept it knowingly. Vanilla and unflavored consistently test lower, and given the cadmium gap this is the cheapest change on the list.

Then look for genuine third-party testing rather than a claim on the tub, because “tested” and “certified” mean very different things and only one of them involves somebody outside the company.

Among the picks in the best clean protein powders, the ones worth starting with here are the brands that publish batch results rather than describing their standards. That’s also where a short ingredient list helps, since the sweeteners and “natural flavors” are a separate question you may as well settle at the same time.

If you’re plant-based by conviction rather than preference, none of this needs to change your mind. Vary the protein source, favor unflavored, and choose a brand that tests. That’s most of the available benefit without giving up the thing you actually care about. Every brand we recommend has a scored profile in our brand directory.

Frequently asked questions

Do all protein powders contain heavy metals?

Most contain detectable amounts, because these metals occur naturally in soil and end up in crops. Testing of 160 powders found nearly half exceeded California’s Proposition 65 limits and roughly a fifth exceeded twice those limits. Detectable is not the same as dangerous, but the range between products is wide, which is what makes brand choice worth something.

Is plant protein worse than whey for heavy metals?

On this measure, yes. Plant-based powders tested with about three times the lead and five times the cadmium of whey-based products. The reason is that plants absorb metals from soil directly, while whey comes from milk. It’s a reason to prefer whey if you’re choosing on this alone, not a reason to abandon plant protein.

Why is organic protein powder worse?

Because organic certification controls what’s applied to a crop, not what’s already in the soil. A field can be free of synthetic pesticides and still carry heavy metals from decades of industrial deposition. In this testing, organic powders averaged three times the lead of non-organic ones.

Is Proposition 65 a safety limit?

No, and this is the fairest criticism of the report. Prop 65 is a California labeling law with deliberately conservative thresholds set well below federal limits. Exceeding it triggers a warning label rather than indicating a product is unsafe. The useful part of the testing is the comparison between products, not the pass/fail line.

Related reading

The rest of this series: what “third-party tested” actually means and the sweeteners and flavors hiding in the tub. For vetted picks, see the best clean protein powders, and our guide to the red flags in the supplement industry covers the wider category.

Sources: Clean Label Project, 2024-25 Protein Powder Category Report, January 2025. Council for Responsible Nutrition, Response to the Clean Label Project’s protein powder report. Consumer Reports, Arsenic and lead found in popular protein supplements.