Oats originates from the Old Continent. The fruit of this plant is used in human nutrition for more than 4000 years because of its rich nutritional composition and the positive effects on the digestive system. Oats contains a high proportion of proteins that are of quality equal to soy protein. It also contains sugars, beta-glucans. These linear polysaccharides are built of D-glucose monomers linked by ß-(13) and ß-(14) glycosidic bonds. The fruit of oats also contains vegetable oils with a high proportion of unsaturated fatty acids, phenolic compounds, saponins, phytic acid, vitamins and minerals. ß-glucan is the most important food fiber in a grain of oats, which is almost completely soluble in water and has the property of forming viscous solutions. Passing through the small intestine ß-glucans remain unchanged because there are no hydrolytic enzymes that can dissolve them, while in the colon their fermentation occurs with bacteria of the intestinal microflora. ß-glucans with the higher molecular weight are soluble in water, and contribute to the higher viscosity of the contents in the small intestine. Because of that a resistant layer is created, and like a physical barrier it prevents cholesterol absorption and reabsorption of bile acids. Consequently, there is increased secretion of cholesterol and bile acid metabolites in the feces, and the increased synthesis of bile acids in the liver. Since cholesterol is a precursor in the synthesis of bile acids, with this process concentration of circulating LDL cholesterol levels reduces. Products of fermentation of ß-glucan in the colon, short chain fatty acids, acetic and propionic acid, cause the inhibition of cholesterol synthesis in the liver. ß-glucans reduce the absorption of glucose from the intestine which reduces the secretion of insulin. Short chain fatty acids, propionic and butyric acids enhance the expression of the transporter GLUT-4 in the muscles by PPAR receptors, thereby reducing insulin resistance. Since insulin resistance is a significant influence on the development of hypertension, ß-glucans can affect blood pressure by modulating insulin metabolism. ß-glucans affect the feeling of satiety by increasing the viscosity of a meal, causing delayed gastric emptying, slow digestion and reduced absorption of nutrients. Short chain fatty acids slow down intestinal motility by stimulating release of the gastrointestinal serotonin. This prolongs the passage of food through the intestines and the feeling of satiety. In addition, short chain fatty acids stimulate different gut hormones that play an important role in the regulation of feeling satiety: PYY, GLP-1, CCK, and ghrelin. ß-glucans are substrate only for beneficial bacteria of the intestinal microflora, while not being in direct interaction with Escherichia colli and other potentially pathogenic bacteria. Therefore, they are classified in the category of prebiotics. Compared to other polysaccharides which act as immunostimulators, ß-glucans are most effective against infectious diseases and cancer. It has been proven that ß-glucans can stimulate the humoral and cellular immunity. Local preparations based on oats have anti-inflammatory effect, reduce skin dryness, itching and peeling. They can therefore be used for the treatment of atopic dermatitis and other skin diseases. For medical purposes other than grain, the green oats is also used. Latest researches have proven that an extract of green oats improves cognitive function in elderly. Finally, this extraordinary plant shows emense potential for the everyday use in nutrition, as well as for the specific applications in the field of pharmaceutical industry.