Protein powder is a supplement, and in the U.S., supplements are regulated far more loosely than food or pharmaceuticals — the FDA doesn't approve them before sale, and manufacturers are largely responsible for their own safety claims. That gap is exactly why independent, third-party testing matters more here than for most grocery items.
What independent testing has actually found
Nonprofit testing initiatives, most notably the Clean Label Project's periodic protein powder studies, have found detectable levels of heavy metals — lead, cadmium, arsenic, and mercury — in a meaningful share of tested protein powders, with plant-based powders testing higher on average than whey in several of these studies. This is generally attributed to soil contamination in the source crops (plants absorb heavy metals from soil more readily than the animals whey is derived from), not deliberate contamination.
Context that matters
Detectable is not automatically dangerous — trace heavy metals appear in a huge range of foods, including rice, leafy greens, and chocolate, well below acute toxicity thresholds. The relevant question is whether levels in a specific product exceed established safe daily limits (like California's Prop 65 thresholds, which are stricter than most other regulatory benchmarks) at realistic serving sizes and frequencies, not whether trace amounts are detectable at all with modern lab sensitivity.
How to actually vet a brand
Look for one of a small number of legitimate third-party certification marks, which indicate a batch has been independently tested against a published standard: NSF Certified for Sport, Informed Sport, and USP Verified are the most recognized. These certifications also screen for banned athletic substances, which matters separately for competitive athletes. A brand publishing its own in-house "third-party tested" claim without one of these recognized certifications is a weaker signal than an actual certification mark.
Practical takeaway
This isn't a reason to avoid protein powder — it's a reason to buy from brands carrying an actual third-party certification rather than the cheapest unverified tub available, particularly for daily long-term use rather than occasional consumption.