Maybe not in a traditional sense, but certainly there are strong social pressures to eat similar things to those around you. Advertising can strongly affect your food choices. Smoking is also not contagious in the sense that it doesn’t immediately give you cancer: it takes years, often decades. Yet we’ve decided to outlaw it in many public places.

Ultimately decisions about diet are made by yourself and affect nobody else (unless maybe you're feeding dependents). Smoking is prohibited in public areas for the same reason that businesses are shuttered now; it subjects others who do not have a choice to a situation that is quite frankly dangerous.