Modulation of tissue prostaglandin synthesizing capacity by increased ratios of dietary alpha‐linolenic acid to linoleic acid,

Abstract

Semipurified diets containing ratios of alpha-linolenic acid (18:3 omega 3) to linoleic acid (18:2 omega 6) of 1/32, 1/7, 1/1, and 3.5/1 in the form of corn oil, soybean oil, soybean/linseed oil mix and linseed oil were fed to rats for 2 months. The first 3 diets were fed to another group of rats for 4 months and to a group through the second generation. Fatty acid analysis of liver and spleen ethanolamine glycerophosphatide revealed that, as the level of 18:3 omega 3 in the diet increased, the elongated, desaturated metabolites of the omega 6 series decreased and the omega 3 series increased. Noteworthy was the depression in the amount of the precursor of the 2-series prostaglandins (PG) as the omega 3 levels increased. Synthesis of PG by liver of rats fed 2 or 4 months markedly decreased, but at 2 months in thymus and spleen, it showed a trend toward decreasing only. Brain slices showed no decrease in PGF2 alpha synthesis after 4 months, but did decrease significantly after feeding the diets to the second generation. Synthesis of PGE2 by spleen homogenate from the second generation also significantly decreased. The replacement of omega 6 series fatty acids by omega 3 series is explained by the effective competition of 18:3 omega 3 over 18:2 omega 6 for the delta 6 desaturase. Depressions in PG synthesis by high dietary 18:3 omega 3 is explained by the competitive inhibition of the PG synthetase complex by 20:5 omega 3 as well as by the decreased levels of 20:4 omega 6.

Differential effects of walnuts vs almonds on improving metabolic and endocrine parameters in PCOS

“…Significant values are in bold. (Marshall and Johnston, 1982). Ratio ALA to LA (1:4) is much higher in walnuts than in the Western diet (1:20).…”

Dietary Intake of ω-6 and ω-3 Fatty Acids and Risk of Colorectal Cancer in a Prospective Cohort of U.S. Men and Women

“…Two recent studies investigating dietary ALA intake (53) and serum ALA levels (33) also found higher risk of colorectal cancer in women but lower risk in men. Although experimental data (18,19,25) have supported the protective effects of both shortchain and long-chain N-3 fatty acids, epidemiologic studies have found inconsistent associations for ALA versus DHA and/or EPA (21,33,53). The potentially inefficient metabolic conversion of nutritionally essential ALA to long-chain N-3's (54) coupled with the absence of ''healthier'' food sources rich in ALA, such as flax, on the FFQ may make it more difficult to evaluate the potential benefits of ALA.…”

“…Experimental studies report anti-inflammatory and anticarcinogenic effects in the colon for N-3 PUFAs [eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and a-linolenic acid (ALA)], highest in fish and seed oils, and adverse effects for N-6 PUFAs [linoleic acid (LA) and arachidonic acid (AA)] found in commercially popular oils and animal products (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Despite evidence supporting the N-6 to N-3 ratio as a biologically plausible target (9,14,16,(18)(19)(20), most epidemiologic studies have generally not found an association with colorectal cancer (21) and very few have been of prospective design (22,23).…”

“…Lowering the N-6 to N-3 ratio is hypothesized to reduce the risk of colorectal cancer, because N-3 fatty acids inhibit the production of proinflammatory, N-6-derived eicosanoids via the cyclooxygenase-2 enzyme (17,18,20,24). Prospective studies and relatively shortterm clinical trials have shown that N-3 fatty acids, particularly the long-chain or marine fatty acids (DHA and EPA), decrease both biomarkers of inflammation (25)(26)(27) and rectal cell proliferation (7,(10)(11)(12)(13).…”

A 22-year Prospective Study of Fish,n-3 Fatty Acid Intake, and Colorectal Cancer Risk in Men

“…In general, eicosanoids produced from arachidonic acid are proinflammatory whereas those produced from n-3 fatty acids are anti-inflammatory (1,33). Because n-3 and n-6 fatty acids compete for both the enzymes that convert shorter-to longer-chain fatty acids (1,34) and the COX-2 enzyme (35)(36)(37), which converts the longer-chain fatty acids to precursors for eicosanoid synthesis, higher n-3 fatty acid intake may result in decreased production of proinflammatory eicosanoids that could play a role in the development of colorectal cancer.…”