DIET AND NUTRITION
Food is obviously needed to sustain life but a balanced diet is vital for good health. General evidence for good nutrition is a well developed body with an ideal weight, good skin, including hair, and muscle tone, and physical and mental alertness. The food eaten by an individual constitutes the diet and it should supply appropriate amounts and proportions of a variety of substances, usually called nutrients. Some nutrients, the macronutrients, such as carbohydrates, lipids and proteins, are required in amounts that are large compared with the micronutrients, such as vitamins, minerals and trace elements, which are needed in much smaller quantities. Nutrients are needed to sustain a number of activities within the body if good health is to be maintained. They supply the raw materials required for growth and maintenance of tissues, include substances that help regulate metabolism, for example the cofactors and coenzymes necessary for enzyme activities and provide the energy to drive metabolism and maintain homeothermy. Nutrients vary in their contributions to these roles and there is also overlap between their contributions to each (Figure 10.1).