Final answer:
WADA and National anti-doping agencies can advise on safe and legal nutritional supplements for use.
Step-by-step explanation:
WADA, which stands for World Anti-Doping Agency, and National anti-doping agencies can provide guidance on which nutritional supplements are safe and legal to use. These organizations are responsible for setting standards and regulations regarding doping and substance use in sports. They conduct research, monitor supplement ingredients, and update their lists of prohibited substances to help athletes make informed decisions. It is essential to consult these authorities and follow their recommendations to ensure compliance with anti-doping rules.