Fats in Human Nutrition

Fat metabolism in man has been the subject of increasing interest and investigation. In the past few years, attention has been directed particularly to the role of fat in the pathogenesis of atherosclerosis. 

Fat is needed in human nutrition for growth and replacement of tissues, for certain lipid secretions, and as a source of energy. The optimal level of fat in the diet is not known, and since fat may be formed from carbohydrate or protein, no definite requirement can be formulated. Fat increases the palatability of the diet and also reduces the bulk, since the energy value of fat is more than twice that of an equivalent amount of protein or carbohydrate. Dietary fat also acts as a carrier for the fat-soluble vitamins. 

In animals, certain unsaturated fatty acids, such as linolenic or linoleic acids, are essential dietary components. Whether these compounds can be synthesized by man has not been determined, but since they are widely present in fats ordinarily consumed, deficiency seems an unlikely possibility. In dogs, there is evidence for a need of fat above that necessary to relieve specific effects of essential fatty acid deficiency (Chapter 7). This may be true in other species, including man. 

Absorption of fat is seriously impaired in man in the absence of bile from the intestinal tract, for example, in obstructive jaundice, although splitting of fat to fatty acids and glycerol proceeds normally. In sprue, idiopathic steatorrhea, and the celiac syndrome, fat is also poorly absorbed, although there is no decrease in available bile and the enzymatic breakdown to fatty acids is unimpaired. It has been suggested that a defective phosphorylating mechanism, due to deficiency of one or more vitamins of the B complex, may account for poor absorption in the sprue syndrome. Folic acid may be one of the factors involved. 

The lipids in the blood during fasting consist largely of phospholipids, cholesterol, and cholesterol esters and almost no triglycerides. After a fat meal, glycerides in the blood increase 300 to 500 mg. per 100 ml. Maximum hyperlipemia is observed 23 to 3 hr. after ingestion of a moderate amount of fat and the fasting level is attained by the fifth hour (Chapter 7). Hyperlipemia depends upon the rate of removal of fat from the blood as well as on the rate of intake. Administration of heparin has been shown to prevent normal alimentary lipemia. This action may be related to the beneficial effect of heparin reported by Jones and associates in patients with atherosclerosis, namely, reduction in the level of certain lipoproteins in the blood. 

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Solderhjelm, L., Wiese, H. F. and Holman, R. T, 1970. Role of polyunsaturated fats in human nutrition and metabolism. Prog. Chem. Fats Lipids 9, 555-682. 

Parodi, P.W. 2004. Milk fat in human nutrition. Aust. J. Dairy Technol., 59, 3-59. 

Brenner, R.R. (1989) Factors Influencing Fatty Acid Chain Elongation and Desaturation, in The Role of Fats in Human Nutrition (Vergroesen, A.J., and Crawford, M., eds.) 2nd edn., pp. 45-79, Academic Press, London. 

Vergroesen, A.J. (ed.) (1975) The Role of Fats in Human Nutrition, Academic Press, London. 

Ackman, R. G. and Ratnayake, W. M. N. (1989) Lipid Analyses Part 1. Properties of fats, oils and lipids recovery and basic compositional studies with gas-liquid chromatography and thin-layer chromatography, in Role of Fats in Human Nutrition (eds A. J. Vergroesen and M. Crawford), Academic Press, New York, pp. 441-514. 

Sickinger, K. (1975) Clinical aspects and therapy of fat malassimilation with particular reference to use of medium chain triglycerides, in Role of Fat in Human Nutrition (ed. A.J. Vergroesen), Academic Press, London, pp. 116-209. 

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