So all the stereotypes are true - people are generally fatter in the South than in NYC. I have vetted this claim with my own eyes, and have even come to discover the source of the issue. The two sources, in fact - somewhat interrelated.
1) They get married very young and have more kids on average. Because they get married so young, they have more time to pop out children and more time to get comfortable with each other - so comfortable that the let themselves go by many tens of inches. I feel like this hypothesis is irrefutably proven by the fact that most people under the age of 21 (that's around marriage age) are skinny-minnies while their parents are hippopotami.
2) They eat/drink things and in quantities that are simply unbelievable to a NYer. For example: The Stacker at my company cafeteria - two grilled cheese sandwiches with a burger patty in between; unlimited buffet ANYTHING - seriously any type of food you want is available in unlimited buffet form. And then there's the soda, which is commonly held in containers larger than my face.
The normal response of a NYer to this picture is: "I can't believe they drink that much soda in one day!" The sad reply is: "They don't just drink one a day - that's why they use refillable containers."