Title: The Omega 6:Omega 3 Ratio

Key words: fatty acids, prostaglandins, linoleic acid, linolenic acid, fish oils, seed oils, coronary heart disease (CHD),

Date: August 2000

Category: 4. Food Data

Type: Article

Author: Dr Mark Draper

The Omega 6:Omega 3 Ratio

Cause for concern in the UK?

It is now considered optimum to consume no more than 20% of our total calories in the form of fat. The current average in Britain is above 40% compared to 15% in countries like Japan, Thailand and the Philippines that have a low incidence of fat-related diseases.(1)

The structures and metabolic pathways of the fatty acids are in the attached appendix.

The Omega 6 and Omega 3 compete for the same pathways and an excess of Omega 6 can lead to an increase in the levels of arachidonic acid and eicosanoid synthesis. The higher levels of prostaglandin PGE2, Prostacyclins (PG12) and thromboxanes may increase inflammations and coaguability. It appears that the Omega 3s increase the levels of Prostaglandin PGE3 and also reduces eicosanoid synthesis.(2)

There are two essential fatty acids: Linoleic acid (LA 18:2w6) and Alpha -linolenic acid (LNA18:3w3). The optimum daily intakes may be 9 to 18 gms and 2 to 9 gms per day respectively (3). The ideal balance between Omega 6 and Omega 3 is thought to be 2:1.

Oily fish contain large quantities of the long chain Omega 3 polyunsaturated fatty acids (EPA and DHA see table unsaturated fatty acids). The low rates of coronary heart disease in various populations with high intakes of fish suggest that these fatty acids possess health preserving properties (4).

Apparently 42% is in the form of Saturated fatty acids (SFA) ; 40% in the form of Monounsatured fatty acids (MUFA); 16% as Omega 6 Polyunsaturated fatty acids (PUFA) and 2.5% as Omega 3 PUFA (a ratio of 6.4 Omega 6:Omega 3).

If a calculation was performed assuming the average UK person ate 140 gms of fat per day then 3.5 gms would be in the form of Omega 3. The Greenland Inuits consume 14 gms per day (3).

In the ideal diet, fat intake should, perhaps, be in equal proportions (33%) SFA , MUFA and PUFA. In North America, the Omega 3 intake in the diet has fallen to one sixth of that in the 1850's and the Omega 6 intake has doubled, changing the ratio of Omega 6 to 3.

The ratio varies between 1:2.5 (Inuit diets) through 6:1 (UK) to 20:1 (contempary safflower and corn oil diets). Although their overall incidence of cardiovascular disease is low, the Inuits do suffer from strokes. This may, however, be due to deficiency of vitamin C and E rather than an increased bleeding tendency due to the effect on thromboxanes and prostacyclins. The Inuits also have a high incidence of osteoporosis. This may be due to their relatively high protein intake.

The ratio in different tissues in the body is as follows; brain 1:1, fat tissues 5:1 and other tissues 4:1. Our enzymes convert Omega 6 only one fourth as quickly as Omega 3. To get equal conversion the ratio should be 4:1 but Omega 6 oils are associated with degenerative conditions so the ratio should favour Omega 3. Perhaps the ideal Omega 6: 3 ratio would be 2:1. If the UK fat intake was halved then 70 gms would have PUFA 24gms with 16 g Omega 6 and 8g Omega 3.

With the present difficulties in obtaining good quality fish and fish oils we should, perhaps, be looking towards organically grown seed oils to increase our levels of intake of Omega 3 (See Table 1: Fat content and fatty acid composition of seed oils). The Omega 3 content of flax (linseed) oil is about 57% and the ratio 1:3. To decrease the dietary ratio of Omega 6 to 3 and to increase the levels of Omega 3, using the uncooked blends of various oils may be the way forward . Another option is to feed hens flax, so that their eggs are Omega 3 enriched.(5) A reduction in dietary animal fats and the trans fatty acids in margarines should also be advised .

Table 1:

* Incudes 9% GLA

** Includes up to 23% GLA

*** Includes up to 5% erucic acid