Because FCS agents teach communities about dietary guidelines, it is important that they are aware of the latest nutrition research. This study assessed FCS agents' knowledge of popular fad diets (low-carbohydrate, intermittent fasting, detoxes and cleanses) and their potential adverse effects, and its relationship among location, certifications, years of experience, professional association memberships, and education. Agents in Louisiana, Texas, Arkansas, and Mississippi were emailed a survey. RDN, DTR, and CHES certifications had significant associations (p = 0.03) with knowledge of adverse effects of fad diets. Agents who hold these credentials may have more knowledge about adverse effects of fad diets.