Aside from the invisible toxic mold that most commonly grows on corn or peanuts, corn has a very bad nutrition profile. The amino acids are not at all balanced and it promotes unhealthy fat deposits instead of healthy muscle tone. That's why they finish large meat animals on corn. It produces "marbling". Lines of fat throughout the muscle for more flavor. A lot of small animals though do not store fat that way and instead pack it in as pure fat around the internal organs so you don't notice until they are really overweight.