<P> The staple food in different parts of the world is a function of weather patterns, local terrain, farming constraints, acquired tastes and ecosystems . For example, the main energy source staples in the average African diet are cereals (46 percent), roots and tubers (20 percent) and animal products (seven percent). In Western Europe the main staples in the average diet are animal products (33 percent), cereals (26 percent), and roots and tubers (four percent). </P> <P> Most of the global human population lives on a diet based on one or more of the following staples: rice, wheat, maize (corn), millet, sorghum, roots and tubers (potatoes, cassava, yams and taro), and animal products such as meat, milk, eggs, cheese and fish . Regional staples include rye, soybeans, barley, oats, and teff . </P> <P> Just 15 crop plants provide 90 percent of the world's food energy intake (exclusive of meat), with rice, maize, and wheat comprising two - thirds of human food consumption . The three are the staples of about 80 percent of the world population, and rice feeds almost half of humanity . </P> <P> Roots and tubers, meanwhile, are important staples for over one billion people in the developing world, accounting for roughly 40 percent of the food eaten by half the population of sub-Saharan Africa . Roots and tubers are high in carbohydrates, calcium, and vitamin C, but low in protein . Cassava root is a major staple food in the developing world, providing a basic diet for around 500 million people . </P>

Which grain is said to be the staple food of more than one-third of the world's population