The corn fed to animals does produce valuable food to people, mainly in the form of dairy and meat products, but only after suffering major losses of calories and protein along the way. For corn-fed animals, the efficiency of converting grain to meat and dairy calories ranges from roughly 3 percent to 40 percent, depending on the animal production system in question. What this all means is that little of the corn crop actually ends up feeding American people. It’s just math. The average Iowa cornfield has the potential to deliver more than 15 million calories per acre each year (enough to sustain 14 people per acre, with a 3,000 calorie-per-day diet, if we ate all of the corn ourselves), but with the current allocation of corn to ethanol and animal production, we end up with an estimated 3 million calories of food per acre per year, mainly as dairy and meat products, enough to sustain only three people per acre. That is lower than the average delivery of food calories from farms in Bangladesh, Egypt and Vietnam.
Jonathan Foely, t’s Time to Rethink America’s Corn System Only a tiny fraction of corn grown in the U.S. directly feeds the nation’s people, and much of that is from high-fructose corn syrup, Scientific American, March, 2013. http://www.scientificamerican.com/article.cfm?id=time-to-rethink-corn