tissues, the fatty acids are either oxidized for energy or used for assembly of the phospholipid molecules that are the primary building blocks of cell membranes. After the bulk of the TAGs are removed, the remainder of the chylomicron particle, termed a remnant lipoprotein and still containing absorbed cholesterol and fat-soluble vitamins, travels to the liver, where it is quantitatively removed from the bloodstream.

The position of the three fatty acids on the three-carbon glycerol backbone of fats is not random, but appears to depend on fatty acyl specificities of enzymes involved in TAG synthesis and to some extent in TAG hydrolysis. These molecules are taken apart and resynthesized several times during their movement into the body, so it is important to recognize that fatty acids in the sn-1 and sn-3 positions are the most labile and most readily available for use in the tissues. The fat in milk gives perhaps the best indication of the relative importance of different fatty acids. The breast milk of most primates that have been studied contains a TAG concentration of about 4 g·dl^-1, which represents about 50% of the GE provided by milk (Wolfe et al., 1993).

Milk fats of several Old World nonhuman primates (including five different macaque species, African green monkeys, Talapoin monkeys, and the sooty mangabey) have been reported to have a fatty acid composition similar to that of the fat in human milk (Buss and Cooper, 1970; Jensen et al., 1980; Smith and Hardjo, 1974a; Smith and Hardjo, 1974b; Wolfe et al., 1993). In the work of Smith and Hardjo (1974b), caprylic (C8:0), stearic (C18:0), oleic (C18:1), and linoleic (C18:2) acid were found predominantly in the sn-1 and sn-3 positions, and lauric (C12:0), myristic (C14:0), palmitic (C16:0), and palmitoleic (C16:1) acids were found in the sn-2 position of the TAG molecule. Linoleic acid made up about 12-13% of the fatty acids, and 80% of this was in the sn-1 and sn-3 positions. The most abundant fatty acid was oleic acid (25-30%), and over 80% of it was found in the sn-1 and sn-3 positions. Palmitic acid was about 20% of total fatty acids and was the most abundant fatty acid in the sn-2 position, representing about 40% of total sn-2 fatty acids. Long-chain polyunsaturated fatty acids were not reported in this study.

Buss and Cooper’s (1970) examination of the milk of Talapoin monkeys revealed a fatty acid composition that differed somewhat from that of milk of the other primate species. Linoleic acid made up about 40% and palmitic and oleic acids about 20% of total fatty acids. The Talapoin monkeys were fed commercial monkey biscuits, a diet low in fat (about 10% of ME) with about 44% of the fatty acids as linoleic acid. Talapoin milk fat contained about 5% more palmitic acid and 5% less oleic acid than the fat in the diet. a-Linolenic acid was found to be 2.5-5.5% of milk fatty acids compared with 7% of fatty acids in the diet.

African green monkeys were fed two fat-enriched diets (40% of ME) containing isocaloric amounts of polyunsaturated or saturated fat (Wolfe et al., 1993). Milk analyses revealed that the dietary fat of the mothers was a major factor in determining the fatty acid composition of their milk, as previously shown in humans (Potter and Nestel, 1976). Linoleic acid was 14% of the total milk fatty acids when dietary fat was enriched in saturated fatty acids and 42% of total milk fatty acids when the diet was enriched in linoleic acid. The increase in linoleic acid in the milk of mothers fed polyunsaturated fat was at the expense of the other major fatty acids in the milk of the saturated fat group. Monounsaturated fatty acids (primarily oleic acid) were 45%, and saturated fatty acids (primarily palmitic acid) 40% of the fatty acids in the milk of the saturated-fat group. Concentrations of both monounsaturated and saturated fatty acids decreased to 28% of total fatty acids in the milk of the polyunsaturated fat group. Birth weight and growth and development of infants in both diet groups were comparable. Thus, the fatty acid shift in the mothers’ diet and in later milk fatty acid composition had no obvious detrimental effects on normal growth of the monkeys (Wolfe et al., 1993). From the perspective of milk fatty acid composition, the data suggest that the types of fatty acids acceptable for primate diets can vary widely, and they provide no support for the contention that linoleic acid levels above 20% of total dietary fatty acids might be harmful (discussed by Innis, 1991).

Primate diets should contain sufficient concentrations of both n-3 and n-6 fatty acids to support normal growth and development. In a study of African green monkeys (Wolfe et al., 1993), dietary ME was present as long-chain n-3 fatty acids (docosahexaenoic acid and eicosapentaenoic acid) at about 0.25%. Another 0.2% of dietary ME was present as a-linolenic acid. That was sufficient to provide the long-chain n-3 fatty acids needed for normal growth and development. Other studies have shown that if all of the n-3 fatty acids in the diet are to be provided in the form of a-linolenic acid, it can take as much as 1% of dietary ME to maintain normal brain and retinal development (Innis, 1991). Those findings are consistent with the observations of Greiner et al (1996) indicating that the efficiency with which docosahexaenoic acid is incorporated into brain and retinal lipids of fetal and infant rhesus monkeys is about 10 times higher than that of a-linolenic acid and the data from Su et al (1999b) showing a 7-fold higher efficiency in neonatal baboons. A large body of literature