What is a major concern regarding the safety of certain supplements?

The major concern regarding the safety of certain supplements, particularly in the context of performance enhancement or health improvement, relates to high levels of pesticides. Many supplements, especially those derived from plants, can contain residues from pesticides if the raw materials are not sourced from reputable growers who adhere to strict agricultural practices. Consumption of supplements with elevated pesticide levels can pose health risks, including potential long-term effects on human health and the environment.

While the other options might present issues in specific contexts, they do not carry the same level of concern related to the safety and efficacy of supplements. For example, high sugar content could be an issue for those monitoring sugar intake for health reasons, but it is not as universal a concern as pesticide contamination. Similarly, low protein levels and low calorie counts might affect the effectiveness of certain products but do not inherently involve safety risks. Therefore, the focus on high pesticide levels underscores a critical aspect of supplement safety and regulation.