The government already does regulate fast food, just like any other kind of food. There are regular health and safety inspection to protect people's health. If a restaurant serves bad food, they'll be shut down. The government also checks the quality of ingredients used in food before they are sent to restaurants.
In the United States, the Food & Drug Administration already regulates the fast food industry in that there are minimum standards for food production in America. Further regulation is not required--free market principles should be observed regarding consumers and choices in fast food restaurants. Not everything is a heart attack on a plate--there are salads and fruits available as well. Regulating fast food is up to consumers.