Riboflavin is one of the B vitamins (vitamin B). The B and C vitamins are the vitamins that dissolve in water. A healthy person's gut can easily take riboflavin from food and pass it on to the blood for the body to use. The body needs the B vitamins to get energy from food. Without riboflavin and the other B vitamins people's bodies cannot use fats, carbohydrates, and proteins.