Is it 'food' when it is in edible form?
It is no sort of necessity at all.
Neither are most of the things you eat, easily substituted with a flavorless soy paste with select added nutrients.
If you grant the government the power to regulate anything you consume, the precedent is established for them to regulate everything.
With Obamacare, what you eat has become part of the 'public good'.
It can also be argued that spices have no food value, with the exception of just enough sodium to keep your electrolytes balanced. Therefore, the government can regulate what (if any) spices you are allowed to use, just for one example.
Now before you say that will never happen, I never thought they'd regulate how much water my toilet flushes, what kind of light bulbs I can get, or whether I'd have to drive with a strap across my lap, but damn, they did it anyway.
I am not going to participate in this silly attempt to compare marijuana to food.