A study shows that many of the top-selling vegan protein powders may contain concerning levels of heavy metals such as arsenic, cadmium, mercury, and lead, and toxins like bisphenol A (BPA), a chemical found in some plastic containers and food can liners.

These substances have been linked to cancer, brain damage, and reproductive issues.

The study from the Clean Label Project found that almost all of the 134 products tested contained detectable levels of at least one heavy metal and 55% tested positive for BPA.

This is not the first research that has shown high contaminant levels in protein powders: A 2010 Consumer Reports’ study detected arsenic, cadmium, lead and/or mercury in samples of all the 15 powders tested.

“These toxins accumulate in your body and can stay there for years,” says Tunde Akinleye, a test program leader in Consumer Reports’ Food Safety Division. “Frequent consumption of foods that contain them can have adverse health effects over the long run.”

The Clean Label Project measured the levels of heavy metals, BPA, pesticides, and other contaminants (more than 150 in all) in protein powders and drinks.

Vegan Protein Powders are The Worse Offenders

Overall, the products made from sources of plant protein such as soy or hemp fared worse than those made from whey (milk) or egg, containing on average twice as much lead and measurably higher amounts of other contaminants.

This is an issue because Vegan protein powders are the fastest growing sector.

Plant-based proteins may have higher contamination levels because the plants are especially prone to absorbing heavy metals from soil. Rice in particular contains more arsenic than any other food and many vegan protein supplements contain a high proportion of rice protein.

Buying Organic Doesn’t Help Either

Buying a product with an “organic” label didn’t help. In fact, organic protein supplements had higher levels of heavy metals, on average, than nonorganic.

“That probably has more to do with these products being plant-based than being organic,” says Callan.

Protein products typically contain between 15 and 25 grams of protein per serving (although some do contain more).

That’s not a difficult amount to get in your diet, if you include natural sources of protein such as legumes, nuts. You’ll benefit not just from the protein itself, but from all the other nutrients found in whole foods.”

Protein Powders and Other Supplements Aren’t Regulated

An additional problem is that supplements in general are only loosely regulated. Though they fall under the purview of the Food and Drug Administration, the agency classifies them differently from drugs. The companies that make and sell them aren’t required to prove that they’re safe, that they work as advertised, or even that their packages contain what the labels say they do.

So, in light of the above it might be time for vegan athletes to review their diets and decide whether they really need to use protein supplements at all.