One of the more interesting and surprising conclusions in my forthcoming book (Hunger Math: world hunger by the numbers) is that hunger is not due to a lack of food in general, but a lack of certain macronutrients. The FAO defines hunger in terms of food energy intake, with 1800 kcal/day as the average minimum for survival. More kcal are needed for good health. The last detailed nation-by-nation FAO Hunger Report (2008) analyzed hunger by macronutrient intake. The most severely afflicted nations lacked sufficient kcal as well as sufficient protein and fat. But the vast majority of the hungry nations had carbohydrate intake within normal limits. Most of the hungry in the world have too little protein, or too little fat, or both.
If a population has insufficient carbs to survive, they are in a state of famine, not hunger. So, by definition, the hungry have enough carbs for survival, though perhaps not enough for good health. Some of the hungry need some additional carbs, because they are teetering on the edge between hunger and famine. But all of the hungry need more protein and/or more dietary fat. Typically, when a population lacks enough calories for good health, but has enough for survival, increasing the dietary fat in their diet will bring their total caloric intake to within normal limits. The need for more dietary fat is the largest part of the hunger problem.
In my analysis of the world agricultural system in terms of macronutrients, I found that the world produces enough kcal for 10 billion people, and enough carbs to feed 13 billion people — but much of that is diverted from human nutrition to feed livestock. The world produces enough protein for 8.7 billion persons, if it were equitably distributed and none were diverted to livestock. But the world produces only enough dietary fat for about 6 billion persons. The macronutrient that the hungry need most is dietary fat, and yet the world agricultural system produces does not produce enough dietary fat for the current world population.
Hunger is primarily due to a lack of dietary fat, and secondarily due to a lack of protein.