Eden H. sent in this image, found at FlowingData, that shows the categories federal ag subsidies fall into, compared to federal recommendations for how often we should eat those types of food (originally found at the Physicians Committee for Responsible Medicine):

Just to clarify, the 73.8% figure for meat and dairy on the left doesn’t refer just to direct subsidies; it also includes subsidies for crops that are grown primarily to feed livestock. The “grains” category (13.23%) refers to grains grown for human consumption. If you included all grains in one category it would be much larger, but somewhat misleading in that the vast majority of grains grown in the U.S. aren’t intended for people to eat.

Without subsidized grain, keeping livestock in confined feeding facilities to fatten them up would be much more expensive, if not entirely cost-prohibitive. Thus, farm subsidies are an essential component of U.S. agribusiness.