The intestine is an important organ with a huge surface area about the size of up to one tennis court. Keeping the balance in the intestine between "inside" and "outside" – the microflora of the bowel and the body – is an extremely important, but also complicated task. To efficiently absorb amino acids, fats and sugar, the surface is considerably enlarged by folds, villi and microvilli on the individual epithelial cells. In addition to this, the intestinal epithelium is only one cell layer thick, and therefore prone to damage. Generally, the body can deal with damage well, as the proliferation rate of the intestinal epithelium – the rate of regeneration through stem cells – is high. On the other hand this leads to an increased cancer risk as these stem cells are especially vulnerable to mutations.