Intestinal flora and human health. There is a growing interest in intestinal flora and human health and disease. The intestines of humans contain 100 trillion viable bacteria. There are two kinds of bacteria in the intestinal flora, beneficial and harmful. In healthy subjects, they are well balanced and beneficial bacteria dominate.
Beneficial bacteria play useful roles in the aspects of nutrition and prevention of disease.
They produce essential nutrients such as vitamins and organic acids, which are absorbed from the intestines and utilised by the gut epithelium and by vital organs such as the liver. Organic acids also suppress the growth of pathogens in the intestines. Other intestinal bacteria produce substances that are harmful to the host, such as putrefactive products, toxins and carcinogenic substances. When harmful bacteria dominate in the intestines, essential nutrients are not produced and the level of harmful substances rises. These substances may not have an immediate detrimental effect on the host but they are thought to be contributing factors to ageing, promoting cancer, liver and kidney disease, hypertension and arteriosclerosis, and reduced immunity.