Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues

Abstract

A method combining data on fatty acid composition into subsets is used to illustrate general relative competitive selectivities in the metabolic and transport events that maintain fatty acid compositions in tissue lipids and to minimize differences among tissues or species in the amount of individual fatty acids. Fatty acid compositions of triglycerides and phospholipids in several tissues of the rat were maintained with simple relationships between the exogenous n-3 and n-6 dietary polyunsaturated fatty acids and the endogenous n-7 and n-9 types of fatty acid. The general pattern of fatty acids in triglycerides was similar for liver, plasma and adipose tissue, averaging about 30% as saturated acids, 67% as 16- and 18-carbon unsaturated acids and only about 2% as 20- and 22-carbon highly unsaturated acids. The tissues maintained a linear relationship between the amount of 18-carbon polyunsaturated fatty acids in the diet and in the tissue triglycerides, with the proportionality constant for 18:3n-3 being 60% of that for 18:2n-6. The total phospholipids of liver, plasma and red blood cells maintained about 45% of the fatty acids in the form of saturated fatty acids and 20-30% as 20- and 22-carbon highly unsaturated fatty acids irrespective of very different proportions of n-3, n-6 and n-9 types of fatty acids. In all three tissues, the 20-carbon highly unsaturated fatty acids of the n-3, n-6 and n-9 type were maintained in a competitive hyperbolic relationship with apparent EC50 values for dietary 18:2n-6 and 18:3n-3 near 0.1% of dietary calories. The consistent quantitative relationships described in this study illustrate an underlying principle of competition among fatty acids for a limited number of esterification sites. This approach may be useful in predicting the influence of diet upon tissue levels of the substrates and antagonists of eicosanoid biosynthesis.

Effects of various dietary n-3 / n-6 fatty acid ratios on the performance and body composition of broilers

“…There was also no statistical difference in the interaction between diet and sex for these parameters. In monogastric animals the fatty acid composition of the tissues will reflect that of the diet (Lands et al, 1990). Analysis of the fatty acid composition of the carcasses and abdominal fat pads showed that palmitic acid (C16:0) was the most predominant saturated fatty acid (Table 6a).…”

“…Linoleic acid (C18:2n-6) was the most predominant PUFA in the tissues (Table 6c). Thomas et al (1987) stated that individuals eating diets containing large amounts of linoleic acid will deposit this component readily in the tissue and complex lipids where it will be elongated and desaturated to arachidonic acid (C20:4n-6) (Lands et al, 1990). Sprecher & Lee (1975) have shown that dietary PUFA are not elongated and then desaturated, but are desaturated and then elongated.…”

“…Also n-3 and n-6 fatty acids have different reaction rates with most enzyme systems (Sprecher, 1991). Linoleic acid is rapidly incorporated into tissue and complex lipids and elongated and desaturated to arachidonic acid (Lands, et al, 1990). α-Linolenic acid is excluded from most tissues and complex lipids (Tinoco, 1982).…”

Choosing foods to balance competing n-3 and n-6 HUFA and their actions

“…Thus, in the absence of competing n-3 nutrients, 0.2 en% of the potent n-6 nutrient maintained more than 50% n-6 in HUFA, and a similar outcome occurred with the equally potent n-3 nutrient in the absence of n-6 nutrients. The impacts of dietary 18:2 and 18:3 on tissue HUFA balance in rats and humans (Lands et al, 1990(Lands et al, , 1992 had similar apparent mid-points (K 18:2 = 0.04 and 0.04, and K 18:3 = 0.07 and 0.06, respectively). The 18-carbon nutrients were very much more abundant than the 20-and 22-carbon nutrients in the foods eaten by the people studied.…”

“…Increased intake of the two major dietary EFA, linoleate and linolenate, expressed as percent of food energy (en%), gave linearly increased weight percent (wt%) contents among the triglyceride acids in plasma, liver and adipose with wt% = C x Xen% S (Lands et al, 1990). The observed value of C x for rats was 2.9 for linoleate (18:2 n-6) and 1.8 for linolenate (18:3 n-3).…”