The balance of polyunsaturated omega-6 and

omega-3 fats in the diet

With respect to fatty acids – balance appears to be important. According to Professor Andrew Sinclair and Professor Artemis Simopoulos, the right balance of omega-6 (n-6) to omega-3 (n-3) fatty acids enables the body to reduce inflammation, lower blood pressure, prevent irregular heart beats and promote healthy blood flow. They also recommend that we increase our intake of omega 3 fatty acids and possibly decrease or not alter our intake of omega 6 linoleic acid. This is because most Australians consume about 10-20g of n-6 fatty acids a day, but only 1-2g of the omega 3's – a ratio of 15 to 1 of n-6 to n-3. For a healthy balance, it is recommended that the ratio should be less than 5 to 1. The most common reason for the imbalance is the widespread use of polyunsaturated oils and spreads. Because they are polyunsaturated they are effective at lowering blood cholesterol, but most of us consume more than enough of them. 

Evidence?

Simopoulos (Prostaglandins Leukotrienes & Ess. Fatty Acids, 1999; 60: 421-9) argues that Palaeolithic people consumed a higher intake of omega 3 fats due to their high intakes of green plants, fruits, nuts, berries, fish and lean meat and a lower intake of omega 6 due to their low intake of cereals and refined oils. Some communities probably also had a high intake of monounsaturated fat from simply pressing the oil out of certain fruits e.g. olives.People living on a Greek island ‘Crete’ in the 1960s at the time of the 7 country study and who ate a traditional Mediterranean diet are believed to have consumed diets high in omega 3 and low in omega 6 fats, similar to that of Paleolithic people. 

In modern society, cereals – mainly wheat, corn and rice – predominate, leading to a relative deficiency of n-3 fats compared with n-6 fats.This imbalance is worsened by the consumption of meat from intensively reared animals fed grain relatively rich in n-6 fats rather than wild plants with a high n-3 fat content. Even farmed fish contain lower amounts of n-3 than those living wild. With the onset of the industrial revolution, saturated fatty acids rose dramatically with the increased availability of red meat, dairy products and hydrogenation of polyunsaturated fats, largely from margarine. Current dietary recommendations to substitute vegetable oils for saturated fat (to reduce serum cholesterol) further favour n-6 over n-3 fats.

Since human genes have changed little, if at all, in the past 10,000 or indeed 40,000 years, then it follows that most people today now eat foods for which they are not genetically programmed. The result, Simopoulos (1999) suggests is chronic disease (diabetes, cancer, obesity, CVD) and believes the n-6 to n-3 imbalance also explains why, although CHD deaths have dropped due to better treatment and secondary prevention, a reduction in recognized risk factors has failed to have an impact on the incidence of myocardial infarction.

The preferred ratio of n-6 to n-3 (<5:1) has been based on the simple logic that this approximates that ratio in our cell membranes and also from evidence regarding food habits of Paleolithic people. However, there has been some further evidence from metabolic and epidemiological studies. Chan et al (Lipids 1993; 28: 811-7) fed three different ratios of n-6 linoleic to n-3 linolenic 27:1,< 7:1, 3:1 in humans. Platelet enrichment with omega 3 eicosapentaenoic acid (EPA) only occurred on the 3:1 ratio. They also compared two diets, one with double the amount of linolenic, but with the same n-6 to n-3 ratio, proving that the ratio not the total quantity is important. In the Lyon Diet Heart Study, the benefits of reducing n-6 fats and increasing n-3 fats (ratio 4: 1) was shown quite convincingly: after 4 years both heart disease and cancer deaths were halved (De Lorgeril et al. Arch Inter Med 1998; 158: 1181-7).

Summary

Medical advice to eat a low-fat high carbohydrate diet can be misleading. The aim instead should probably be for a diet that, regardless of its fat content, contains an increased amount of omega 3 fatty acids (a reduced amount of saturated fat) and to prefer carbohydrate containing foods with a low-medium glycaemic index.

More evidence is needed on the ideal n-6: n-3 ratio. Nevertheless, it is probably prudent advice to recommend an increase in the intake of foods high in omega 3 fats.

Last Updated: March27, 2001.