Obesity in this country is closely linked to poverty. The foods that people in poverty have access to (because of cost but also because of food deserts) offer excessive calories but poorly balanced nutrition.
That means that people are obese but at the same time essentially starving to death from lack of nutrients. Which causes more food cravings that people are able to attempt to satiate only with more food with poor nutritive value.
I think obesity dis-proportionally affects impoverished African Americans vs. other impoverished races.
At least based on one point of anecdata - my neighbors. I have lots of poor families in my neighborhood even though I am middle class myself thanks to HOC (a Maryland social program where middle class housing is subsidized for the poor). Long story short - my poor African American neighbors are extremely obese; and it's no wonder why. I only ever see them eating McDonald's/dollar tree chips/soda. I know they are on SNAP, but I don't know if they are trading it for booze/cigarettes. It's my opinion though that they lack education on how to prepare/cook cheap raw ingredients into meals.
Yet my other equally poor immigrant El Salvadorian neighbors are skinny as rails and from what I can tell they eat tons of rice and beans and such (I often see them carrying 20 lb bags of rice into their house).
There is definitely a genetic component. A very clear example is the obesity rate of Pacific islanders after they were introduced to the western diet. They were genetically isolated while subsisting on a very specific diet for thousands of years. As a result, they no longer thrive on the same diet that Europeans do.
That means that people are obese but at the same time essentially starving to death from lack of nutrients. Which causes more food cravings that people are able to attempt to satiate only with more food with poor nutritive value.