In the paper there are discussed the structure and properties of red betalain pigments: betacyanins, occurring in the plants belonging to certain families of the Caryophyllales order. People consume the betacyanins containing plants either raw or in the form of canned food and vegetable concentrates. Moreover, the extracts of betacyanin pigments are added to food products as natural colouring preparations. In Europe, the beetroot (Beta vulgaris L. subsp. vulgaris) is the most popular source of betacyanins. In this paper, the biological activity of those compounds was highlighted as were probable mechanisms of their effects on the human body. A possible absorption and circulation model of betacyanins in the human body was suggested. Furthermore, some data were presented, which referred to anticancer activity of betacyanins and their role in preventing degenerative diseases and cancer.