What nutrition provides

Human nutrition supplies both raw materials and energy. Carbohydrates and lipids can be oxidised in respiration, proteins provide amino acids for growth and repair, vitamins and mineral ions support particular chemical and structural functions, fibre assists movement through the gut, and water acts as a solvent and transport medium. A food can contain several nutrients, so it is more accurate to discuss its main dietary contributions than to call it simply a carbohydrate or protein.

Carbohydrates, lipids and proteins

Carbohydrates are important immediate energy sources. Lipids are concentrated energy stores, provide insulation and contribute to membranes. Proteins are required to make enzymes, antibodies, some hormones and structural materials. Protein may also be respired, but using it primarily as an energy source is inefficient because nitrogen-containing waste must be removed.

Vitamins and mineral salts

Vitamin C supports healthy connective tissues and wound healing. Vitamin D helps the body absorb and use calcium for bones and teeth. Calcium also contributes to muscle and nerve function, while iron is needed to make haemoglobin. These micronutrients are required in small amounts, but their absence can have large effects.

Fibre and water

Fibre is not digested by human enzymes. It adds bulk to gut contents and helps peristalsis move material through the intestine, reducing constipation. Water dissolves substances, participates in reactions, transports materials in blood and tissue fluid, and supports temperature control through sweating. Water is obtained from drinks, food and metabolic reactions.

Reading diet questions

When asked for a nutrient source, give a specific food or food group. When asked for importance, state the biological role. Do not confuse source with function. For example, iron is found in meat, beans and leafy vegetables; its importance is that it is required for haemoglobin and therefore oxygen transport.

Review questions and suggested answers