Which substance is not a nutrient but is essential for digestion?

Fibre is considered essential for digestion, though it is not classified as a nutrient in the same way that carbohydrates, proteins, fats, vitamins, and minerals are. Instead, fibre is a type of carbohydrate that the body cannot digest. While nutrients provide energy and are vital for growth and maintenance of body functions, fibre plays a crucial role in maintaining digestive health. It adds bulk to the stool, helping to regulate bowel movements and prevent constipation. Furthermore, fibre aids in the digestion of other nutrients by promoting a healthy gut environment.

Water, protein, and vitamins are direct sources of nutrition required by the body for various metabolic processes. Water is essential for hydration and plays a role in facilitating various bodily functions, including digestion. Protein is necessary for building and repairing tissues, while vitamins serve as co-factors in many enzymatic reactions. Hence, they are classified as nutrients, which distinguishes them from fibre, which supports but does not directly contribute to nutritional intake.