Human Biochemistry Volume 2 - Murray R. 1993

Special Topics
Nutrition, Digestion, and Absorption
Lipid Requirements

Although Lipids frequently provide a significant portion of the daily energy requirement, this is not their primary function.

Dietary lipids enhance the palatability of food, induce satiety, and fulfill two additional vital Functions in Human Nutrition. They act as dietary Solvents for Fat-soluble Vitamins and serve as a source of essential polyunsaturated Fatty acids, which the body cannot synthesize. These include (at least in some animals) linoleic acid (ω-6, 18:2), α-linolenic acid (ω-3, 18:3), and arachidonic acid (ω-6, 20:4). These acids are found within the lipids of PLANT AND ANIMAL products (see Table 15.2). For a Structure/133.html">Discussion of their METABOLISM, see Chapter 24.

In humans, arachidonic acid is formed primarily from linoleic acid and is not essential provided that linoleic acid is present in the diet in sufficient quantities. Debate continues as to whether α-linolenic acid should be classified as a truly essential fatty acid for humans. Linoleic acid deficiency is rare; the likelihood of such a condition increases in infants receiving skimmed milk and in patients receiving fat-free intravenous nutrition.

Essential Fatty Acids are critically important as precursors of Leukotrienes, Prostaglandins, and thromboxanes (see Fig. 24.6), which function as "local Hormones." A diet that provides 1–2% of Energy Requirements as essential fatty acids prevents the clinical manifestations of their deficiency.

Lipids and Disease. Numerous studies have revealed a correlation between CORONARY Heart DISEASE, Blood Cholesterol levels, and fat intake, particularly of saturated fats (see Chapter 27). High fat intake is also associated with breast and colon Cancer. The primary sources of saturated fats in the human diet are ruminant meats, dairy products, and hard margarine. Cholesterol is present exclusively in foods of animal origin, especially in egg yolks.



Last update: 06/08/2026

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