Topic 7.1 · Core
Diet
A balanced diet is not a bigger portion of food, and it is not simply “eating your vitamins.” It is a diet that supplies the different dietary components the body needs in proportions suited to that individual — and the proportions, not the total amount, are what an exam answer actually needs to name.
A balanced dietcontains the required nutrients, fibre and water in appropriate proportions for the body’s needs. For this syllabus, that means suitable amounts of carbohydrates, fats and oils, proteins, vitamins C and D, calcium, iron, fibre and water. Notice what that list does not say: it does not say equal amounts of everything, and it does not say more food. A larger portion of an already unbalanced meal is still unbalanced, and a diet can fail the definition in either direction — through deficiency or through excess — not only by leaving something out.
Carbohydrates, fats and proteins
| Nutrient | Principal sources | Importance |
|---|---|---|
| Carbohydrates | rice, bread, cereals, pasta, potatoes and other starchy foods | major source of energy for respiration |
| Fats and oils | vegetable oils, nuts and seeds, butter and other fatty foods | concentrated energy source and store; also provide thermal insulation |
| Proteins | meat, fish, eggs, dairy products, beans and pulses | growth and repair of tissues |
Carbohydrates and fats can both be respired for energy, which is exactly why they are not interchangeable with protein. Protein’s defining dietary importance here is growth and repair, not energy supply — a distinction worth holding onto, since the syllabus asks for the specific importance of each nutrient rather than a shared, generic answer.
Vitamin C and vitamin D
Vitamin C comes principally from fresh fruits and vegetables, especially citrus fruits, and it is important for maintaining healthy tissues. A prolonged lack of it in the diet causes scurvy. Vitamin Dcomes from oily fish, egg yolk and fortified foods, and can also be produced in the skin on exposure to sunlight — so, unusually among the nutrients on this list, diet is not its only source. Vitamin D supports healthy bones and teeth and the body’s normal use of calcium. A lack of it in children causes rickets.
Calcium and iron
Calcium comes mainly from milk and other dairy products, and is needed for strong bones and teeth. Ironcomes from red meat, some green leafy vegetables and pulses, and its required importance here is specific: iron is needed to make haemoglobin, the oxygen-carrying pigment in red blood cells. Swapping these two roles — putting calcium with haemoglobin, or iron with bones — is the single most common lost mark in this section, so it is worth anchoring each mineral to only one function: calcium to bone and tooth strength, iron to haemoglobin. Calcium and vitamin D are related, since vitamin D supports the body’s normal use of calcium, but they are not the same substance and do not share one function.
Fibre and water
Fibre, sometimes called roughage, comes mainly from wholegrain foods, fruits and vegetables. Most of it is not digested — its value is physical rather than chemical, adding bulk to the contents of the gut and helping material move through the alimentary canal. Water comes from drinks and water-rich foods, and acts as a solvent, a medium for chemical reactions, and the means by which substances are transported around the body in solution. Both belong on the list of what a balanced diet must supply in their own right — a diet described only as carbohydrate, fat, protein, vitamins and mineral ions is incomplete without them.
Scurvy and rickets
A deficiency disease results when the diet does not supply enough of a specific required nutrient — not from “eating badly” in some general sense, but from the absence of one named substance. The two required links for this chapter are precise and should be stated exactly this way: a lack of vitamin C causes scurvy, and a lack of vitamin D causes rickets. A lack of calcium can also contribute to poor bone development, but vitamin D deficiency is the specific link this syllabus requires you to state for rickets, so calcium belongs in an answer as a contributing factor, never as a replacement for it. Reversing the two pairings — vitamin C with rickets, or vitamin D with scurvy — is the standard way this point loses marks, so it is worth checking the direction of each link before moving on.
Once the diet has supplied these components in the right proportions, the next question is how the body actually gets them out of food — which starts with how the digestive system is organised and what ingestion actually means.