I should have worded that a bit better, only a very small proportion is used for direct human consumption.
Approx 20% of the total us harvest is used for seed, ethanol or human consumption, and only a percentage of that is used for food products. The numbers vary year by year as they are subject to industry and environmental changes. The U.S. Corn Council states that for the 12/13 season 34 million metric tons of corn was used for human consumption, seed and other non ethanol products while 219 million metric tons were used for ethanol, livestock feed and residual products.
This was taken from epa.gov:
According to the National Corn Growers Association, about eighty percent of all corn grown in the U.S. is consumed by domestic and overseas livestock, poultry, and fish production. The National Corn Growers Association also reports that each American consumes 25 pounds of corn annually. The crop is fed as ground grain, silage, high-moisture, and high-oil corn. About 12% of the U.S. corn crop ends up in foods that are either consumed directly (e.g. corn chips) or indirectly (e.g. high fructose corn syrup). Corn has a wide array of industrial uses including ethanol, a popular oxygenate in cleaner burning auto fuels. In addition many household products contain corn, including paints, candles, fireworks, drywall, sandpaper, dyes, crayons, shoe polish, antibiotics, and adhesives.
While it might seem that we use a huge amount of these grains in our everyday eating habits, it is vastly less than the amounts used in everything else. My point being, we can try all we want to enact labeling and safe food laws but it makes no difference because all the proposals only cover what we directly consume with no thought to indirect consumption. About the only way around it is to produce all of your own food and never eat corn. It does not matter what the label says all corn seed produced in the us has been tainted by cross pollination.
We only eat 25 pounds (approx 11kilos) annually and the average 500 pound (approx 225kilo) cow would consume 3500 pounds (1590kilo) annually. The actual numbers behind the 7-10:1 ratio is staggering.