Fat intake

Dietary fat includes not only the obvious fat in the diet (the visible fat on meat, cooking oil, butter or margarine spread on bread), but also the hidden fat in foods. This latter may be either the fat naturally present in foods (e.g. the fat between the muscle fibres in meat, the oils in nuts, cereals and vegetables) or fat used in cooking and manufacture of foods. There are two problems associated with a high intake of fat:

  • The energy yield of fat (37 kJ/g) is more than twice that of protein (16 kJ/g) or carbohydrate (17 kJ/g). This means that foods which are high in fat are also concentrated energy sources. It is easier to have an excessive energy intake on a high-fat diet, and hence a high-fat diet can be a factor in the development of obesity (see Chapter 6).
  • There is good epidemiological evidence that fat intake is correlated with premature death from a variety of conditions, including especially atherosclerosis and ischaemic heart disease and cancer of the colon, prostate, breast and uterus.

From the results of epidemiological studies, it seems that diets providing about 30% of energy from fat are associated with the lowest risk of ischaemic heart disease. There is no evidence that a fat intake below about 30% of energy intake confers any additional benefit, although a very low-fat diet is specifically recommended as part of treatment for some people with pathological hyperlipidaemia.

As an aid to reducing fat intake, a number of low-fat versions of foods that are traditionally high in fat are available. Some of these are meat products which make use of leaner (and more expensive) cuts of meat for the preparation of sausages, hamburgers and pies. Low-fat minced meat (containing about 5—10% fat by weight, instead of the more usual 20%) is widely available in supermarkets, although it is, of course, more expensive, and low-fat cheeses and pates are also available, as are salad dressings made with little or no oil. There are also a number of low-fat spreads to replace butter or margarine. Skimmed and semiskimmed milk are now widely available, providing very much less fat than full-cream milk, although full-cream milk is an important source of vitamins A and D, especially for children.

A more recent advance has been the development of compounds that will replace fat more or less completely while retaining the texture and flavour of traditional fatty foods. Two such compounds are Simplesse, which is a modified protein used in low-fat spreads but is not suitable for cooking, and Olestra (also known as Olean), which is a fatty acid ester of sucrose (and hence chemically related to fats; section 4.3.1) but is not absorbed. It is stable to cooking and can be used to prepare fat-free potato crisps etc.

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