There are lots of different types of fat in the diet, including what are know as “polyunstaturated” fats. These fats come in two major forms in the diet: omega-6 and omega-3. The main omega-6 fatty acid in the modern-day diet is known as linoleic acid. Rich sources of linoleic acid include plant oils such as hemp, pumpkin, sunflower, safflower, sesame, corn, walnut and soya oil. Omega-6 fat also comes in the form of what is known as ‘arachidonic acid’, which is found in foods such as meat, fish and seafood. The major omega-3 fatty acids in the diet come in the form of alpha-linolenic acid (from plant sources such as flaxseed and rapeseed) and fats known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) that are mainly found oily varieties of fish.

Omega-6 and omega-3 fats don’t have just different names, they also have reasonably distinct action in the body. Both are metabolised into hormone-like substances known as eicosanoids (pronounced ‘eye-coz-ah-noids’), which themselves come in a variety of forms (including substances known as prostaglandins, prostacyclins, leukotrienes and thromboxanes). Eicosanoids that come from the omega-6 fats tend encourage physiological processes such as inflammation, blood vessel constriction and clotting in the body (all of which tend to promote disease such as cardiovascular disease in the body).

On the plus side, eicosanoids from omega-6 fats are balanced by the effect of those from omega-3 fats, as these tend to be anti-inflammatory in nature, and they have blood vessel-relaxing and blood thinning effects too. Because omega-6 and omega-3 fats have broadly opposing action within the body, a ‘balance’ between these fats is vital for optimal health.

There is some debate about what the ideal balance between these two fats should be. What we do know though is that primitive diets (which probably reflect the ideal ratio) have a much lower omega-6:omega-3 ratio than the typical Western diet. It is estimated that the primal diet contained a ratio of omega-6 to omega-3 fats of about 1-3:1. However, the fact that we are generally eating far more in the way of omega-6 fats and, almost certainly, less omega-3 too, has led to this ratio increasing to between 20:1 and 30:1 in a typical Western diet. The importance of this may be profound, when one considers that higher omega-6:omega-3 ratios are associated with an increased risk of ‘cardiovascular’ conditions such as heart disease and stroke [1]. Other evidence points to a raised omega-6:omega-3 ratio as a potentially important underlying factor in type 2 diabetes [2]. This fatty imbalance has also been implicated in inflammatory conditions and autoimmune disease - conditions where the body’s immune system reacts against its own tissues such as rheumatoid arthritis [3].

I was interest to read a study published this month in which individuals were tested with a diet with a lower omega-6:omega-3 ratio than normal. These healthy volunteers were asked to cut back on their omega-6 consumption, and at the same time eat 3 meals containing oily fish each week. In addition, they were asked to supplement with rapeseed oil at a dose of 20 mls a day, which provided them with a reasonable dose of the omega-3 fat alpha linolenic acid [4]. The study lasted 10 weeks.

Before and the study and at its conclusion the researchers measured a variety of disease markers in the study subjects. Notably, the intervention led to a statistically significant increase in a substance known as adiponectin. This hormone is secreted by fat cells, and has been shown to have generally benefical effects on the body’s physiology an anti-inflammatory effect. Inflammation appears to be a key underlying process in cardiovascular disease, and there is some evidence that higher levels of adiponectin are associated with a reduced risk of this condition.

Adiponectin also stimulates the breakdown of fat in the body. Interestingly, this study also found that the prescribed diet led to a boost in the rate at which the subjects burned fat. In the fasted state, fat burning went up by 28 per cent. While this did not lead to a significant reduction in the fat mass carried by the subjects, it should be borne in mind that all the subjects were of “healthy” weight (BMIs 20-25) and are unlikely to have had too much spare fat to lose. This study was hampered somewhat in not have a control group. Though, the authors also cite evidence that omega-3 supplementation can prevent or even reverse weight gain in animals.

This study adds to the current body of evidence which suggests that a lower omega-6:omega:3 ratio in the diet that we are accustomed to is likely to have benefits for health including, perhaps, a reduced risk of cardiovascular disease and improved body composition.

References:

1. Weber PC. Are we what we eat? Fatty acids in nutrition and in cell membranes: cell functions and disorders induced by dietary conditions. In: Fish fats and your health. Norway: Svanoy Foundation, 1989:9–18

2. Raheja BS, et al. Significance of the n-6/n-3 ratio for insulin action in diabetes. Ann N Y Acad Sci 1993;683:258–71

3. Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids Biomed Pharmacother. 2002 56(8):365-79

4. Guebre-Egziabher F, et al. Nutritional intervention to reduce the n-6/n-3 fatty acid ratio increases adiponectin concentration and fatty acid oxidation in healthy subjects. Eur J Clin Nutr 2008;62:1287-1293

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