Read this great article from Time magazine
Here is an excerpt:
So what’s wrong with cheap food and cheap meat — especially in a world in which more than 1 billion people go hungry? A lot. For one thing, not all food is equally inexpensive; fruits and vegetables don’t receive the same price supports as grains. A study in the American Journal of Clinical Nutrition found that a dollar could buy 1,200 calories of potato chips or 875 calories of soda but just 250 calories of vegetables or 170 calories of fresh fruit. With the backing of the government, farmers are producing more calories — some 500 more per person per day since the 1970s — but too many are unhealthy calories. Given that, it’s no surprise we’re so fat; it simply costs too much to be thin.