Wheat is the most widely grown cereal grain, occupying 17 % (220 million hectares in 1994) of the cultivated land in the world. Wheat is planted on about 100 million hectares in the developing world, excluding the countries of Central Asia and the Caucasus. It is the staple food for 35% of the world's population and provides more calories and protein in the world's diet than any other crop. The uniqueness of wheat in contrast to other cereals is that its kernel contains a gluten that makes it possible to produce a wide array of end products. The two most common kinds of wheat are bread wheat and durum wheat.