The ratio of n-6 to n-3 polyunsaturated fatty acids in the rat diet alters serum lipid levels and lymphocyte function
The ratio of n-6 to n-3 polyunsaturated fatty acids in the rat diet alters serum lipid levels and lymphocyte function
Year: 1996
Authors: N M Jeffery, P Sanderson, E J Sherrington, E A Newsholme, P C Calder.
Publication Name: Lipids
Publication Details: Volume 31; Number 7; 737.
Abstract:
Numerous publications have shown that feeding n?3 PUFA from flaxseed oil (rich in ALA) or fish oil (rich in EPA and DHA) positively influences serum blood lipid levels and immune function in animal models and in humans. Specifically, flaxseed oil and fish oil consumption inhibits a number of lymphocyte functions such as proliferation, interleukin?2 production, natural killer (NK) cell activity, and antigen presentation; effects which have benefit in reducing symptoms associated with rheumatoid arthritis, multiple sclerosis and psoriasis. The objective of the present study was to further confirm these findings. In the present study, male rats were fed basal diets which contained one of five high fat (20% by weight) portions made by mixing various levels of flaxseed oil and sunflower oil (rich in LA). The resulting blends had n?6/n?3 PUFA ratios of 112:1 (pure sunflower oil); 14.8:1; 6.5:1; 0.8:1 and 0.33:1 (pure flaxseed oil). Following the six week feeding period, rats fed the pure flaxseed oil showed the lowest final body weights and total dissectible fat. Serum cholesterol, triglycerides and nonesterified fatty acid concentrations decreased as the n?6/n?3 PUFA ratio of the diet decreased. TG levels in animals fed the pure flaxseed oil diet were 40% lower than the TG levels of animals fed the pure sunflower oil diet. A progressive increase in ALA and a decrease in LA and AA in the fatty acids of serum lipids and spleen lymphocytes occurred as the dietary n?6/n?3 PUFA ratio decreased. A significant suppression of spleen lymphocyte proliferation in response to the T?cell mitogen, concanavalin A, and in spleen lymphocyte NK cell activity was noted as ALA content of the diet increased. A maximum reduction of ex vivo spleen lymphocyte proliferation of 65% was observed following the diet containing a n?6/n?3 PUFA ratio of 14.8:1. The localized graft vs. host response, a measure of cell?mediated immunity in the body, progressively decreased as the dietary n?6/n?3 PUFA ratio decreased. This study indicates that dietary flaxseed oil consistently lowers blood lipid levels. The authors postulated that this may result through enhanced oxidation of fatty acids as ALA is a better substrate for ??oxidation than is LA. As a result of enhanced fatty acid oxidation, lower amounts of fatty acids are available for hepatic TG synthesis which may lead to reduced serum lipid levels. The reduction in adipose fat deposition observed in animals fed the pure flaxseed oil diet may also be a result of lowered levels of circulating TGs available for deposition. In the present study, suppressed lymphocyte function and diminished NK cell activity was believed to be due, in part, to a reduction in AA synthesis with concomitant decreases in leukotriene B4 with the inclusion of ALA in the diet. Leukotriene B4 is a potent activator of NK cell activity. The authors suggest that ALA in flaxseed oil is as potent as EPA and DHA in dietary fish oils with regard to blood lipid levels and immune cell function and that only a relatively small amount of dietary ALA is required to bring about positive effects.
