Yes, we are overfed, but we're also very undernourished. I remember in junior high school health class a long time ago, learning how serious alcoholics consume most of their calories from alcohol and can suffer from nutritional deficiencies, but most of us are not much better off. The SAD (Standard American Diet) is so highly processed and full of "empty calories" from high-fructose corn syrup and hydrogenated vegetable oils that many of us are not much better fed than that alcoholic. I have read studies of the diets of children and teens that show up to 40% of their calories coming from sugar. Frightening.

The SAD eating folks would also suffer from gross nutritional deficiencies if it weren't for the synthetic vitamins and minerals that we "fortify" our foods with that prevents the worst nutritional deficiencies like scurvy or beriberi from appearing. Even avoiding processed foods is not a total solution. Our Industrial Agriculture practices produce fruits and vegetables now that have fewer nutrients in them than what our parents ate in their youth, to say nothing of the taste difference. The meat situation is similarly degraded.

Peak Oil will lead to less food and a declining population. Essentially, the solar energy from millions of years of shining down on the Earth, converted and locked up in coal, oil or natural gas, is now converted into food calories by our Industrial Agriculture system. As the fossil fuels, particularly oil, begin to decline in output, so does the extra food that feeds billions of people. You need more energy input to create more energy output in the form of food. Simple physics.