A nutritional composition is disclosed which comprises synergistic functional carbohydrates for preventing or treating infection by pathogenic bacteria and/or promoting gut flora balance and health. The carbohydrates have a synergistic activity on promoting bifidobacteria in the intestine. Also disclosed are a method of production of the composition; and a method of treatment of infection by pathogenic bacteria and/or promoting gut flora balance and health which comprises administering an effective amount of the composition.