Why does the body need vitamins even when food supplies enough calories?

Answer: Vitamins support essential chemical reactions and regulation

Vitamins provide an extra supply of fuel calories — Vitamins themselves are not a source of fuel calories. Carbohydrate, fat and protein can supply energy, but having enough of that fuel does not guarantee enough vitamins.

Vitamins support essential chemical reactions and regulation ✓ — Vitamins are needed in small amounts for essential processes that calories cannot replace. Many B vitamins help enzymes process nutrients, while vitamin D helps regulate calcium absorption. Different vitamins do different jobs; they are not all simply enzyme helpers.

Vitamins supply most of the material used to build tissues — Vitamins do not provide most of the bulk material in tissues. Protein and minerals supply structural materials, while vitamins help the body use nutrients and maintain normal functions.