A new report by the Institute of Mechanical Engineers (mentioned at Treehugger.com) claims that 30 to 50% of all food produced by the world agricultural system is wasted:
“Today, we produce about four billion metric tonnes of food per annum. Yet due to poor practices in harvesting, storage and transportation, as well as market and consumer wastage, it is estimated that 30–50% (or 1.2–2 billion tonnes) of all food produced never reaches a human stomach.” (IME Report)
Is this true? According to my analysis, the world agricultural system produces just over 1.0E+16 kcal per year (Comparison of World Staple Crops). If we allot 2740 kcal/person-day, that figure is 1.0E+6 kcal/person-year. Thus 1.0E+16 kcal per year can feed 10 billion persons, at least in terms of kcal produced. The proper apportionment of those kcal among the three macronutrients is another matter.
If we feed 7 billion persons on an amount of food sufficient to feed 10 billion, then about 43% of that food was wasted (10/7=1.43). But we have nearly 1 billion persons who are chronically undernourished in the world. They eat less food than they need. By my estimate (in my book: Hunger Math), the 1 billion hungry have about 65.5% of the kcal that they need. This implies that we are really only feeding, in essence, 6.655 billion persons. So our world agricultural system produces food for 10 billion, but feeds 6.655 billion. Therefore, about 50% of the food is wasted (10/6.655=1.50).
The above cited report uses a completely different method to calculate the amount of food wasted, and yet it arrives at much the same conclusion. By my calculations, the wasted food is 40 to 50% of all food produced; an estimate of 30% is too low.