The truth is, existing federal programs appear to have very little to do with eating habits. Years of research on the effects of SNAP (formerly Food Stamps) on diet concluded that SNAP participants eat more (as is the point of the program), but not very differently from their neighbors.
Likewise, a new USDA report released last week concludes that participation in the federal school meals programs is "not significantly related" to students' waistlines.
But just because these programs "do no harm" doesn't mean they can't be leveraged to improve public health.
For example, today's New York Times examines the growth in the use of SNAP benefits at farmers' markets across the country. And here in Texas, a new federal program is bringing farmers' market coupons to low-income elderly in Witchita Falls (1, 2) among other cities.