Protein supplements are big business. Globally, consumers spent $12.4 billion in 2016 on various powders, bars, and other aids intended to support muscle-building exercise. But as a new report by Clean Label Project and examined by Consumer Reports points out, many of these products may also have you ingesting undisclosed ingredients like lead and arsenic.

Clean Label Project—a non-profit organization that examines truth in food labeling—reviewed 134 popular protein supplements on the market and looked for more than 130 possible toxins, including lead, pesticides, and bisphenol A (BPA). The results: 70 percent of the products contained detectable levels of lead, 74 percent had cadmium, which is thought to be an endocrine disruptor; and 55 percent contained BPA, an industrial chemical associated with health problems.

Products labeled “organic” often had much more of the contaminants than non-organic products—up to 1.5 times more lead and arsenic, and up to 4.8 times more cadmium. These substances can linger in the body and have been identified as carcinogens; exposure to BPA can promote a greater risk of cardiovascular problems.

The report found that protein from egg sources was less likely to carry the toxins than plant-based (hemp or soy) supplements, a likely consequence of plants absorbing heavy metals from soil. The highest-scoring products—those with the least amount of contaminants—were whey-based.

According to Consumer Reports, some trace of heavy metals is expected in protein powders and it’s not possible to eliminate all of it, but powders with markedly higher levels are lacking in processing methods to keep as much out as possible. If you take protein for fitness, you may want to consider getting your desired intake through whole foods. If your diet requires supplementation owing to illness or gastric issues, try to find supplements with the least amount of unwanted metals. Puori PW 1 Pure Whey Vanilla Protein, for example, took the top spot in Clean Label’s testing.

You can check out a breakdown of Clean Label’s results in the infographic below.

A Clean Label Project infographic explaining the contaminants found in protein powders
Clean Label Project