According to Wikipedia:
No exact reason was given as to why Richman retired, other than moving on and wishing his audience farewell. Explaining the show's re-tooling to become "Man V. Food Nation", Scripps Networks chairman Ken Lowe cited concerns over ensuring Adam Richman's health if the show had continued in its previous format. Richman had since turned vegan, and reportedly lost about 60 pounds.
So glad he gave up all the food challenges. IMO vegan isn’t the wisest choice, but it’s better than restaurant food.
I started working in food service at age 16 and am back in that world after a 20 break. Even in locally owned fine dining establishments it’s extremely hard to find healthy options. My requests embarrass my husband on the rare occasions we eat out, but I have a pretty good idea of what’s in the kitchen-corn syrup and trans fats all around.