Which of the following lists correctly identifies the six classes of nutrients?

• A. Carbohydrates, proteins, fats (lipids), vitamins, minerals, and water
• B. Carbohydrates, proteins, fats, minerals, and vitamins only
• C. Carbohydrates, proteins, vitamins, minerals, water, and fiber
• D. Carbohydrates, fats, minerals, vitamins, and carbohydrates

Answer: (A)

The six essential nutrient classes are carbohydrates, proteins, fats (lipids), vitamins, minerals, and water. Carbohydrates provide the body’s main energy source; proteins supply amino acids for tissue growth and repair and for enzyme and hormone production; fats offer concentrated energy and essential fatty acids needed for various bodily functions; vitamins act as coenzymes and regulators of many metabolic processes; minerals serve as cofactors for enzymes, support bone and fluid balance, and enable electrical signaling; and water is essential for hydration, digestion, circulation, temperature regulation, and serving as the medium for most biochemical reactions. Some lists include fiber, but fiber is a type of carbohydrate rather than a separate essential nutrient class, so a set that treats six distinct categories as listed above is complete. A list that leaves out water or fats or repeats carbohydrates, for example, would be missing a key nutrient class and not be complete.