If Obama truly wants to limit obesity to help health care costs, make Soda-Pop, chips, candy and anything with corn-syrup in it off limits from a government run Food Card (food stamps) purchase. rant/
Just for Food Card purchases? Have you really thought about this? I worked as a cashier at Meijer for nearly a year. I noticed that people with Bridge Cards tended to buy healthier foods than people who shopped with the cards. I saw more produce, organic or soy milk, whole wheat breads, organic eggs, etc. in the carts of people who had the card. My theory is that the Bridge card doesn't cover non food items, leaving all the money for food. The Food Stamp program was helping these families actually afford healthy foods.
Maybe your idea should be expanded to all customers. Why not just ban junk foods, soft drinks, transfats, etc? Nitrates, high fructose corn syrup, refined flower, sugars, etc. Just ban the stuff, anything unhealthy, and give incentives to restaurants, especially fast food places, to serve healthy foods.
Stopping poorer people from buyin the foods you mentioned isn't going to solve America's obesity problem because obesity is a problem all across class lines. And yes, America does have class lines.