A simpler and probably legal solution - modifying food stamps to limit food purchases like WIC. You only get fresh fruit, vegetables, low fat milk, low fat cheese and healthy items. No more junk food or pre-prepared food. Given that 20% of households receive food stamps, and poverty correlates to obesity, this type of change could be made in the name of both health and cost savings.
Fine and smart idea. I can hear the complaining already.