Many chronic diseases – particularly obesity, diabetes mellitus and cardiovascular disease – cause premature mortality and morbidity and are potentially preventable by dietary change.

Box 5.2 suggests the composition of the ‘ideal healthy diet’. The values given are based on the principle of:

• reducing total fat in the diet, particularly saturated fat
• increasing consumption of fish which contain n-3 (or ω-3) polyunsaturated fatty acids
• increasing intake of whole-grain cereals, green and orange vegetables and fruits, leading to an increase in fibre and antioxidants.

Reductions in dietary sodium and cholesterol have also been suggested. There would be no disadvantage in this, and most studies have suggested some benefit.

Fortification of foods with specific nutrients is common. In the UK margarine and milk are fortified with vitamins A and D, flour with calcium, iron, thiamin and niacin, and breakfast cereals with several vitamins and iron. Not all substances used in fortification have nutritive value. For example, Olestra is a polymer of sucrose and six or more triglycerides which has been introduced to combat obesity. It is not absorbed and is therefore used particularly in savoury snack foods (where it has FDA approval) as a ‘fake fat’. Therefore, it results in a reduction in total calories. It has side-effects (mainly in the gut) and its use is being carefully monitored.

Box 5.2 Recommended healthy dietary intake

Dietary component	Approximate amounts (% of total energy unless otherwise stated)*	General hints
Total carbohydrate	55 (55-75)	Increase fruit vegetables, beans, pasta, bread
Free sugar	10 (< 10)	Decrease sugary drinks
Protein	15 (10-15)	Decrease red meat (see fat below)
Total fat   Saturated fat   Unsaturated fat	30 (15-30) 10 (< 10) 20	Increase vegetable (including olive oil) and fish oil and decrease animal fat
Cholesterol	< 300 (< 300) mg/day	Decrease meat and eggs
Salt	< 6 (< 5) g/day	Decrease prepared meats and do not add extra salt to food
Total dietary fibre	30 (> 25) g/day	Increase fruit and vegetables and wholegrain foods

* Values in parentheses are goals for the intake of populations, as given by the WHO (including populations who are already on low-fat diets). Some of the extreme ranges are not realistic short-term goals for developed countries, e.g. 75% of total energy from carbohydrate and 15% fat.

The interests of the individual are often different from those associated with government policy. A distinction needs to be made about nutrient goals and dietary guidelines. Nutrient goals refer to the national intakes of nutrients that are considered appropriate for optimal health in the population, whereas dietary guidelines refer to the dietary methods used to achieve these goals. Since dietary habits in different countries vary, dietary guidelines may also differ, even when the nutrient goals are the same. Nutrient goals are based on scientific information that links nutrient intake to disease. Although the information is incomplete, it includes evidence from a wide range of sources, including experimental animal studies, clinical studies and both short-term and long-term epidemiological studies.

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