This intriguing article from the New York Times blames farm subsidies, which often favour junk high carbohydrate foods, as the reason for record US obesity.
Payments for farmers were started in the 1930s during the Depression to help save family farms but now it costs billions and benefits 1/3 of the nation’s farmers. The 2002 farm bill provided $143.3 billion for nutrition programs like Food Stamps, $16.8 billion for conservation and $67.6 billion to subsidize planting of certain crops. Most subsidies go to 5 commodities: soybeans, corn, rice, wheat and cotton. Fruit and vegetable farmers get none.
Critics say the subsidies lead to cheap snack foods and soft drinks, made from ingredients like high fructose corn syrup and partially hydrogenated soybean oil. Meanwhile, the lack of subsidies for fruits and vegetables makes them expensive by comparison. From 1985 - 2000 the cost of fresh fruits and vegetables increased 40% while the price of soft drinks decreased by almost 25% adjusted for inflation.
Calories from those subsidized foods are partly responsible for the epidemic of childhood obesity and the increased incidence of diabetes.