Poor diet and lack of excercise I would imagine.

Judging from solely her skin color, she's probably living in a low-income community. In the US, many grocery stores do not operate in very bad/poor neighborhoods because it isn't worth it. The people in the neighborhood are so poor they can barely afford to go the grocery store as it is, and because of that many grocery stores in those areas face significant amounts of robberies (especially because robbers know that a retail store or grocery store really can't do much to stop you) so then grocers decide "fuck you" and close up shop.

Then the only places where one can buy food in the "ghetto" are gas stations and fast food outlets. Why pay $3 for 4 oranges when you can pay 15 dollars and get a 10 piece bucket of chicken plus 2 sides.

So basically you have a situation in which there is nowhere within miles to buy food. If she's really really poor then she doesn't have a car either, which means she can't drive to a nicer, whiter, part of town to buy food at a decent grocery store. So she is consigned to buy food where she can.

It's a sad situation but a reality that happens in almost every major urban city in America, or at least the midwest/rust belt.