Metabolism
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Fats and oils - are all fats the same?
Why do we need fat in the diet?
The main reason that there is a need for fat in the diet is that on a very low fat diet, providing less than about 10% of energy intake, it is difficult to eat a large enough bulk of food to meet energy requirements. Fat provides 37 kJ /gram, compared with 16 kJ /gram from carbohydrate and 17 kJ /gram from protein. In addition, carbohydrates and proteins in foods are associated with a considerable amount of water, while high-fat foods contain much less, and many carbohydrate-rich foods are also sources of non-starch polysaccharides, which add to the bulk of the food without providing a significant amount of energy.
We can add to this a number of other reasons:
Vitamins A, D, E and K, as well as carotenes and other lipid-soluble compounds are absorbed dissolved in dietary fat, and indeed fatty foods are the main sources of these nutrients.
Much of the flavour of many foods is contained in the fat.
Fat lubricates the food in the mouth, and makes chewing and swallowing easier.
Two families of polyunsaturated fatty acids cannot be synthesised in the body, and are required as precursors for the synthesis of prostaglandins and related compounds.
Conversely, there is a considerable body of evidence that excessively high intakes of fat, around 40% of energy or more, as was typical of western diets towards the end of the 20th century, are associated with a significantly increased risk of developing chronic non-communicable diseases - the so-called diseases of affluence, including:
atherosclerosis and coronary heart disease
hypertension and stroke
obesity and the metabolic syndrome, leading to the development of type II diabetes mellitus