Grains require less energy to produce than most other foods. They tend to be inexpensive, however, which means people have little incentive to avoid waste. Consequently, a large percentage of this food category goes unused.
Although vegetables require more energy than grains to produce, they are still relatively energy lean. Because they spoil easily, about one fourth of this food group is wasted.
Fruits are even more energy intensive than vegetables, and they are relatively more expensive. However, because fruits spoil easily, a significant fraction is still lost.
Nuts have a long shelf life, during which they aren't prone to spoilage. Consequently, less than one sixth of this crop is wasted, which helps extend the payoff of the relatively high amount of energy needed to produce it.
Dairy products are three times as energy intensive as grains to produce. Dairy is very prone to spoilage, and people are wary about consuming potentially spoiled milk and other foods; consequently, a third of dairy products is wasted, despite their high price.
Meats, poultry and fish are energy intensive—more than four times that of grains and twice that of vegetables—because land animals, at least, first require investment in feed or grazing. Although meats are prone to spoilage, comparatively little is wasted because their high price discourages such profligate behavior.
Eggs are the most energy intensive of the seven major food categories. They are also expensive. But nearly a third of them are wasted because nobody wants to risk eating a rotten egg.