7: Land and Water Use
FEEDING A GROWING POPULATION
In order to feed a population adequately, a couple of factors must be taken into
account. The following sections discuss these in detail.
Human Nutritional Requirements
A healthy diet generally requires 2,500 calories per day for the average male and
2,000 calories per day for the average female. Proper nutrition also requires a
balanced intake of protein, carbohydrates, and fat. Protein produces 4 calories of
energy per gram and should make up about 30% of all calories. Carbohydrates
also produce 4 calories of energy per gram and should make up approximately
60% of the daily diet. Fats produce 9 calories of energy per gram and should not
make up more than 10% of the total daily caloric intake.
Only about 100 species of plants of the 350,000 known are commercially grown
to meet human nutritional needs. Of these, wheat and rice supply over half the
human caloric intake. Just 8 species of animal protein supply over 90% of the
world’s needs. It takes about 16 pounds (7 kg) of grain to produce 1 pound (0.5
kg) of edible meat, and 20% of the world’s richest countries consume 80% of the
world’s meat production. About 90% of the grain grown in the United States is
grown for animal feed. By consuming the grain directly instead of consuming
the animals that feed upon it:
■ There would be a 20-fold increase in the amount of dietary calories and an
8-fold increase in the amount of protein available.
■ Less rangeland would be required (e.g., 40% of all the rainforests have
been cleared in the last 40 years, mostly for cattle pasture).
■ There would be less negative impacts on the land (e.g., land compaction,
desertification, overgrazing, erosion, nutrient loss).
■ There would be less of an impact on the world’s clean water supplies. For
example, producing one pound (0.45 kg) of beef requires 1,799 gallons
(6,810 L) of water. As a comparison, producing one pound of corn
requires only 108 gallons (409 L) of water.