Title: Problems associated with the delivery of long chain N-3 polyunsaturated fatty acids in our diet

 

Key words: fish oils, n-3 polyunsaturated fatty acids, PUFA, coronary heart disease, CHD, fish, fish oils, vegetable oils, spreads, trout, mackerel, salmon, dioxins, mercury, PCBs, mustard seed oil, soya oil, flax seed antioxidants, fruit, vegetables, Mediterranean diet, linoleic acid, eicosopentaenoic acid,  

 

Date: Oct 2006

 

Category: Macronutrients, Specific conditions

 

Nutrimed Module:

 

Type: Article

 

Author: Morgan, G

 

Problems associated with the delivery of long chain N-3 polyunsaturated fatty acids in our diet

 

The beneficial effects of fish oils and a diet rich in n-3 polyunsaturated fatty acids (PUFAs) on cardiovascular disease have been known for some time. Siscovitch et al.(1997), for example, showed an inverse relationship between the consumption of fish oils and the incidence of coronary heart disease (CHD). Large trials, such as the DART trial (Burr 1989), were largely instrumental in persuading medical and governmental bodies to revise their recommendations to the general public regarding the ideal levels of saturated and unsaturated fat intake. Thus, with regard to the levels of long chain n-3 PUFAs in the diet, recommendations were made to increase the consumption of fish, the consumption of 1-2 oily fish per week being considered adequate to meet the additional requirement for these fatty acids (Department of Health 1994). 

 

Cultural and socio-economic factors have made it difficult for these modest targets to be met. In a survey of the dietary habits in this country (Gregory 1990), it was found that only 65% of the population were fish consumers. Although aware of the cardiac benefits of increased consumption of the n-6 PUFAs, in the form of vegetable oils and spreads, increases which had made significant improvements to mortality rates in the USA and other developed countries since the 1970s (Riemersma 1992), it appeared that the population was far less willing to increase its consumption of the long chain n-3 PUFAs. This was particularly disappointing given that large trials such as the GISSI trial (1999) have shown that consumption of as little as one oily fish per week makes a significant difference to cardiac mortality.

 

Differences in consumption of both the n-3 and n-6 PUFAs have been shown to be lowest in the poorer and less well-informed lower socio-economic groups, groups where the incidence of CHD is highest (Riemersma 1992). Economic and social factors have largely contributed to this situation. Thus, although medical and governmental promotion has been largely been successful in encouraging a switch to n-6 PUFA rich spreads and oils which are quite affordable, the increasing scarcity and price of fish has deterred many social groups from making fish part of their weekly diet. This is particularly the case for salmon and the less popular oily fish such as trout or mackerel.

 

Cultural factors such as the decline in smoked herring have also had an effect, along with concern over the levels of fish contaminants such as mercury, PCBs and dioxins. It is not known what quantative effect oxidation of these long chain n-3 PUFAs has on their delivery. Prolonged storage and such practices as deep-frying would be expected to diminish their availability. In light of the above, further education regarding the use and benefits of fish consumption is obviously to be recommended. More economic means of farming fish may help to promote fish consumption. So may novel ways of combining fish with other n-3 PUFAs. Singh et el. (1997), for example, in an Indian population was able to show a significant fall in CHD in subjects taking relatively low intakes of fish with mustard seed oil. Increased use of flax seed and soya oil may well have the same effect.

 

From the European perspective, further encouragement to switch to the so-called Mediteranean diet is to be recommended. Such a diet, with a high content of fruit, vegetables and vegetable oils, is not only rich in linoleic acid but also in antioxidants, which both impair fatty acid oxidation and have a cardio-protective effect in their own right. Such short chain n-3 PUFAs are able to generate the long chain PUFA eicosopentaenoic acid. In future such long chain n-3 PUFAs may well be incorporated into new palatable spreads and oils so that the present imbalance in n-3 and n-6 consumption is corrected and the inherent difficulties of encouraging fish consumption circumvented.

 

References

1. Siscovick DS et al. Dietary intake and cell membrane levels of Long-chain n-3 polyunsaturated fatty acids and the risk of Primary cardiac arrest. 1995 JAMA 274: 1363-1367

2. Burr ML et al. Effects of changes in fat, fish and fibre intakes  on death and myocardial infarction: diet and reinfarction trial (DART). 1989 Lancet ii, 757-761

3. Department of Health. Diet and risk. 1994 in Dietary reference  values for for food energy and nutrients for the United Kingdom. Report on health and social subjects no. 46, pp. 123-144. London. H.M. Stationary Office

4. GregoryJ, Foster K, Tyler H & Wiseman M. The dietary and nutritional survey of British adults. 1990 London. H.M. Stationary Office

5. Riemersma RA. Polyunsaturated fatty acids and coronary heart  disease. 1992 The Third International Congress on Essential Fatty Acids and Eicosanoids, Adelaide, Australia

6.  GISSI-Prevenzione Investigators. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. 1999 Lancet 354 : 444 455

7. Singh B et al. Randomised, double-blind, placebo controlled trial of fish oil and mustard oil in patients with suspected acute myocardial infarction: the Indian experiment of infarct survival - 4 1997 Cardiovascular drugs and therapy 11: 485- 491