The next calculation starts with the world's total grain and oilseed production. Animals eat much of both. Although producing food from the feed, they consume more than they produce. In 1988 in the United States, according to national statistics, cattle consumed the equivalent of 13 kg of maize to produce 1 kg of beef. The national ratios of feed to meat ranged from about 3 for broilers and 6 for hogs up to 19 for sheep (U.S. Department of Agriculture, 1991, 57). Catfish, which need little energy to keep a constant temperature or keep their place, produce meat with even less feed than do broilers: Lovell tabulated ratios of feed to weight gain of 10 for beef cattle, 2.1 for broilers, and 1.2 for channel catfish; catfish and broilers converted the protein in feed into food with about the same efficiency (Lovell, 1988,[Lov88] 6, 11).
Cattle and sheep digest grass and other roughage that a human cannot, and fish can graze and consume plankton. Nevertheless, let us examine how many calories and grams of protein the world's grain and oilseed would furnish humanity if people ate it all rather than sharing it with farm animals or fish.
The USDA (1993[USD93]) estimated that in 1991 the world produced 1,695 million t of grain and 222 of oilseeds. To translate these quantities into calories and protein, I multiplied the weight of grain and oilseeds by the energy and protein in wheat and soybeans. The 1991 production of grain and oilseeds would provide an average 2,107 cal/day to ten billion people, an average near the present consumption in Honduras or Pakistan but at the low end of the range of recommended daily allowances.
If the protein in the grain and oilseeds produced in 1991 were divided among ten billion people, the average would be 86, still more than the 71 reaching people today.
Clearly, if they shared the food reaching present consumers, the ten billion people would not be able to spare even the present land occupied by Nature. If the 1991 production of grain and oilseeds were consumed wholly by people, the ten billion would get adequate protein and barely adequate calories.