Heavy Metals in Protein Powder: What the Numbers Actually Mean

By Dr. Eugene Capitano, DC, MSc

Every year or two, a headline lands: independent testers found heavy metals in protein powder. The reaction splits predictably — alarm on one side, dismissal on the other. Neither is useful if you are simply trying to decide what to buy.

So here is the calm version: where these metals come from, what the published numbers actually say, which products test highest and why, and — the part almost nobody explains — what the thresholds being quoted actually measure.

Why they are there at all

Lead, arsenic, cadmium and mercury are elements in the Earth’s crust. They enter soil and water through natural weathering and volcanic activity, and are concentrated further by mining, industry and some agricultural practices. Plants take them up through their roots. Animals take them up through feed and water.

That means trace amounts appear in ordinary food — rice, leafy greens, cocoa, root vegetables, seafood — not just supplements. A protein powder is an agricultural product that has been concentrated, so whatever was in the raw crop or the milk supply arrives concentrated too. There is no growing method that produces zero.

What the largest published survey found

The most substantial recent dataset is the Clean Label Project’s 2024–25 Protein Powder Category Report, which tested 160 top-selling products from 70 brands — roughly 83% of the US market — across more than 35,000 individual analyses.

The headline number: 47% exceeded at least one federal or state regulatory threshold for safety, including California Proposition 65, and 21% measured over twice the Proposition 65 level for lead.

The breakdown is more instructive than the headline:

• Plant-based powders: 77% tested over the Proposition 65 lead threshold
• Whey powders: 28%
• Collagen: 26%
• Chocolate-flavoured: 65% (29% over twice the threshold)
• Certified organic: 79% — averaging roughly three times the lead of non-organic products

Two of those deserve explanation, because they surprise people.

Why plant protein tests higher than whey

It is not a quality failure — it is botany. Plants absorb metals directly from soil through their roots, so a plant protein concentrates whatever the soil held. Dairy sits one step further along the chain: a cow’s digestive tract and liver filter a substantial portion of dietary metals before anything reaches milk.

A 2026 analysis of 30 sports protein supplements published in Environmental Research found the same pattern independently: plant-derived products averaged higher lead (0.18 vs 0.06 mg/kg) and cadmium (0.05 vs 0.01 mg/kg) than dairy-derived ones (Chen et al., 2026; PMID 41655677). That study sampled the Chinese market and tested only 30 products, so it should not be read as describing North American shelves — but the direction of the difference matches the much larger CLP dataset.

The organic finding follows from the same logic: organic certification governs pesticide and fertiliser inputs, not soil geology. It says nothing about the lead already present in the ground, and the CLP result was driven largely by organic products being disproportionately plant-based.

Why chocolate is consistently the worst category

Cacao is an unusually efficient accumulator of cadmium, and to a lesser degree lead. Cadmium is taken up from soil by the cacao tree — concentrations vary enormously by growing region — while lead contamination is associated more with post-harvest handling and drying. This is why chocolate powders show up at 65% over threshold when the category average is 47%, and why the single worst outlier in the 2026 Environmental Research analysis was a brown-rice-and-cocoa product (lead 0.60 mg/kg, cadmium 0.15, arsenic 0.30).

It also means a chocolate protein powder is the formula most worth asking questions about — including ours. We test the cocoa on the way in like every other ingredient, and we deliberately kept the inclusion rate conservative to leave margin against the thresholds rather than sitting just under them.

Rice deserves its own paragraph

Rice is the most efficient accumulator of inorganic arsenic in the plant kingdom — it grows in flooded paddies, and flooding changes soil chemistry in a way that makes arsenic far more available to the plant. Rice protein is common in plant blends because it complements pea’s amino acid profile cheaply.

When we screened a rice ingredient and measured it per serving against Proposition 65 levels, it came back higher than we were willing to accept. We removed it and rebuilt the profile with pea, methionine and leucine instead of diluting it to pass. The longer version of that decision is here.

What Proposition 65 thresholds actually are

This is the part almost every article skips, and it changes how you should read every number above.

Proposition 65 is a California disclosure law. It requires a warning when exposure to a listed chemical exceeds a defined level. Those levels — called safe-harbour levels — come in two kinds: a Maximum Allowable Dose Level (MADL) for reproductive toxicity, and a No Significant Risk Level (NSRL) for cancer risk. For lead, the MADL is 0.5 micrograms per day; the cancer NSRL is 15 micrograms per day — a thirty-fold difference for the same metal.

Three consequences follow, and they matter:

1. Exceeding a Proposition 65 level is not the same as being unsafe. It is the point at which California requires a warning label. The levels are deliberately conservative — the lead MADL is set with a thousand-fold safety margin below the level shown to cause observable harm.
2. “Over Prop 65” is meaningless without knowing which number. A product over the 0.5 µg MADL and a product over the 15 µg NSRL are in very different places. Reputable reports specify; marketing claims often don’t.
3. It is a California law, not a national standard. Nothing obliges a Canadian company to use it. Some of us use it anyway because it is among the most conservative benchmarks available in North America — which makes it a useful hard line rather than a judgement call.

So when you see “47% exceeded Proposition 65 thresholds,” the accurate reading is: 47% of tested products contained enough of a listed metal that California would require a warning label — not “47% of protein powders are dangerous.” That is still a meaningful and unflattering finding about the category. It just isn’t a poisoning story.

How to read an actual lab report

If a brand publishes lot-level results — and you should prefer ones that do — here is how to interpret what you’re looking at:

• Check the units. Results usually appear as mg/kg or ppm (parts per million) in the powder. To convert to what you actually consume, multiply by your serving size in kg. A result of 0.05 mg/kg in a 40 g serving is 0.002 mg — 2 micrograms.
• Check whether it’s the ingredient or the finished product. These are different tests answering different questions. Blending changes the profile.
• “Not detected” is not zero. It means the amount was below what that method could reliably measure. A good report states the detection limit alongside the result. This is why no honest brand claims “heavy-metal free” — a laboratory result is a measured number, not a promise of absence.
• Check the date and the lot. A report from three years ago describes a lot that is long gone. Per-lot reporting is the only version that tells you about the bag in your hand.

What this means practically

Nobody needs to stop using protein powder over this. The realistic takeaways are narrower and more useful: plant proteins carry higher category risk than dairy and deserve more scrutiny; chocolate and rice-containing formulas deserve the most; “organic” tells you nothing about metals; and the only claim worth anything is one attached to a report you can actually open, for the lot you actually bought.

Our own approach — what we test, who tests it, what standard we measure against, and where the honest limits are — is set out in what “third-party tested” actually means. The reports themselves live on our Batch Quality & Reports page.

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DISCLOSURE

Dr. Eugene Capitano is Co-Founder and Scientific Lead of TLC PureOrigin™ and Founder of TLC NeuroMicrobiome Labs Inc. This commercial relationship should be considered when evaluating commentary about protein products, ingredients and formulation.

Educational content only; not intended to diagnose or treat disease. Consult a qualified professional before major dietary changes.

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References

Chen, M., Dong, R., & Lai, W. (2026). Heavy metal and microplastic exposure from sports protein supplements: Integrated health risk modeling and scenario analysis. Environmental Research, 295, 123988. (PMID 41655677)

Clean Label Project. (2025). CLP Insights: 2024–25 Protein Powder Category Report.

California Office of Environmental Health Hazard Assessment. Proposition 65 safe harbor levels: No Significant Risk Levels and Maximum Allowable Dose Levels. oehha.ca.gov/proposition-65