The mixture of food and drink consumed by an individual. Variations in morbidity and mortality between population groups are believed to be due, in part, to diﬀerences in diet. A balanced diet was traditionally viewed as one which provided at least the minimum requirement of energy, protein, vitamins and minerals needed by the body. However, since nutritional deﬁciencies are no longer a major problem in developed countries, it seems more appropriate to consider a ‘healthy’ diet as being one which provides all essential nutrients in suﬃcient quantities to prevent deﬁciencies but which also avoids health problems associated with nutrient excesses.
Major diet-related health problems in prosperous communities tend to be the result of dietary excesses, whereas in underdeveloped, poor communities, problems associated with dietary deﬁciencies predominate. Excessive intakes of dietary energy, saturated fats, sugar, salt and alcohol, together with an inadequate intake of dietary ﬁbre, have been linked to the high prevalence of OBESITY, cardiovascular disease, dental caries, HYPERTENSION, gall-stones (see GALL-BLADDER, DISEASES OF), non-insulindependent DIABETES MELLITUS and certain cancers (e.g. of the breast, endometrium, intestine and stomach) seen in developed nations. Health-promotion strategies in these countries generally advocate a reduction in the intake of fat, particularly saturated fat, and salt, the avoidance of excessive intakes of alcohol and simple sugars, an increased consumption of starch and ﬁbre and the avoidance of obesity by taking appropriate physical exercise. A maximum level of dietary cholesterol is sometimes speciﬁed.
Undernutrition, including protein-energy malnutrition and speciﬁc vitamin and mineral deﬁciencies, is an important cause of poor health in underdeveloped countries. Priorities here centre on ensuring that the diet provides enough nutrients to maintain health.
In healthy people, dietary requirements depend on age, sex and level of physical activity. Pregnancy and lactation further alter requirements. The presence of infections, fever, burns, fractures and surgery all increase dietary energy and protein requirements and can precipitate undernutrition in previously well-nourished people.
In addition to disease prevention, diet has a role in the treatment of certain clinical disorders, for example, obesity, diabetes mellitus, HYPERLIPIDAEMIA, inborn errors of metabolism, food intolerances and hepatic and renal diseases. Therapeutic diets increase or restrict the amount and/or change the type of fat, carbohydrate, protein, ﬁbre, vitamins, minerals and/or water in the diet according to clinical indications. Additionally, the consistency of the food eaten may need to be altered. A commercially available or ‘homemade’ liquid diet can be used to provide all or some of a patient’s nutritional needs if necessary. Although the enteral (by mouth) route is the preferred route for feeding and can be used for most patients, parenteral or intravenous feeding is occasionally required in a minority of patients whose gastrointestinal tract is unavailable or unreliable over a period of time.
A wide variety of weight-reducing diets are well publicised. People should adopt them with caution and, if in doubt, seek expert advice.