[michaelpinto]

Genetics plays a role in obesity:

https://en.wikipedia.org/wiki/Genetics_of_obesity

You can also be thin and have a bad diet, and while you may not be obese your internal systems can still be suffering from damage over the long run.

Something that should be noted: Many folks who are poor don't have access to high quality foods. So they can buy soda but not a salad. And what determines what makes those foods cheap or expensive are often driven by industry lobbying. So much so that when there was attempt to tax soda in NYC there was a great deal of money spent to stop that from going into effect.