If all you can afford is ramen/bread/fast food, your body makes you overeat to get enough other nutrients (eg. vitamin C, B).
The second is that your insulin goes crazy with all those simple carbs and sugars (carbs are cheap, unlike protein, fish and vegetables, and get metabolised to glucose) so you get massive blood sugar swings. The low side of those makes you eat more and get fatter.
Lottery tickets are a strawman. Or, to quote a science fiction novel that I can't quite remember: "a tax on hope."
It's just as cheap to eat properly as it is to eat unhealthily. The difference is you need to actually put some effort in, rather than order a large Big Mac Meal.
Complex carbohydrates are cheap. Fat is cheap. Eating simple carbohydrates is not an economic choice.
Vitamins pills and vegetables are reasonably cheap. And anyway if deficiencies caused obesity, the rate would drop off dramatically over some threshold income.
Lotteries matter because that's where poor Americans spend about 10% of their income. Taxing the rich to destruction will not fix that.
Yes, in fact good food can be extremely cheap. Beans, eggs, and butter are dirt cheap. Canned vegetables are affordable if you buy for nutrition (i.e., not empty food like green beans).
Re. lottery spending, they are losing $12 a week! That is $600 a year! That could buy premium multivitamins, an extra several eggs a day, rather a lot of cheese, with money left over for the occassional meal out.
The problem of most poor Americans is not resources, it is the deployment of them.
Do you think they spend so much on lottery tickets because the rich so unfairly keep them out of derivative trading?