Perhaps some data to back that up? Some of the best restaurants and chefs in the world are American. Have you been to an American grocery store of any reasonable quality? The cheese selection of many big-city grocery stores rivals even French grocery stores. I shop in France all the time and I am still amazed at the variety at many American grocery stores. Try finding Napa/Chinese cabbage, fresh chiles, daikon radish or any number of ethnic staples in a typical French grocery store -- its very difficult. I love my local grocery store but for sheer variety, American wins big.
This tired trope about Americans eating so much processed food is often passed around by people that seem to not be very familiar with what grocery stores in the rest of the world sell. The French have entire stores dedicated to pre-packaged, frozen meals. Stereotypes are often based in truth, but that doesn't mean they are true.
Your average American grocery store has the ingredients to make almost any cuisine on earth, yet I have to import tortilla flour from the US because the only thing resembling Mexican food in France is "Old El Paso." Korean ingredients? Good luck with that. There's a tired section of soy sauces that consist of Kikkoman generic crap and that's about it. In a US store, I can find at at least 5 different kinds of soy sauces. Actual Asian noodles as well.
People seem to have a hobby bashing Americans, yet the American grocery store is a temple to the success of capitalism, world trade and diversity.
Ever been to a "non-capitalist" grocery store in China? Once you do that, then perhaps you could opine on how bad capitalism is for food.
Capitalism is the very reason you can find enoki mushrooms in Omaha, habaneros in Minnesota or Serbian rakija in Los Angeles.
I am not saying that Americans always make the best nutritional choices -- but it isn't due to the lack of opportunity to do so.