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Omega-3 fatty acids: why are they so important?

Carol Ottley
BSc SRD RPHNutr
State Registered Dietitian and Registered Public Health Nutritionist
E:cao.foodcomm@ virgin.net

For many years dietary advice has included the message to cut down on saturated fat and swap to polyunsaturated oils and spreads. As consumers and food manufacturers have responded to this advice there has been an increase in the use of polyunsaturated oils such as sunflower and corn oil, and a drop in traditional fats such as butter and lard. All well and good you might think, but this shift in the balance of fats consumed has resulted in a relative lack in the diet of fats known as the omega-3s. As research reveals the wide range of important functions these fats have in the body, it is time to redress the balance and ensure that people are getting enough omega-3 fatty acids.
 
What are omega-3 fats?
Omega-3s are a family of polyunsaturated fats (PUFAs) derived from the essential fatty acid a-linolenic acid. The long-chain versions, known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are the ones that provide beneficial effects in the body.

The other main family of PUFAs are the omega-6 fats derived from another essential fatty acid, linoleic acid. These two families of fats compete for the same enzymes during metabolism, which means that a relative excess of one family will mop up important enzymes needed by the other. In recent years intake of omega-6s has risen substantially while the intake of omega-3s has fallen.(1) We now consume about 16 times more omega-6 fats than omega-3s, and this imbalance is likely to have an important impact on our health.

Where do we find omega-3s?
The richest source of the long-chain omega-3s, EPA and DHA, is oily fish (see Table 1). However, only about one-third of the UK population eat oily fish, and the latest National Food Survey found that our average weekly intake is only 14g.(2) As the COMA report on cardiovascular disease recommends one portion (about 130g) of oily fish per week,(3) this means we are currently consuming just 11% of what the government recommends for heart health. Another recent survey also confirmed that children are the least likely to be consuming adequate levels of oily fish.(4)

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So there needs to be a substantial increase in the consumption of oily fish by the majority of people if we are going to achieve government recommendations. Clearly for the fish-phobic and vegetarians, other strategies are necessary.

EPA and DHA can also be made in the body from ­
a-linolenic acid, which must be provided from the diet - flax (linseed) oil, rapeseed (canola) oil, soya oil and walnuts are particularly good sources. However, apart from choosing the right cooking and salad oils, the range of foods available to boost omega-3 intake is small. Fortunately there are now foods available that are fortified with omega-3s. One way of doing this is the addition of microencapsulated fish oils to foods such as spreads and breads. Another successful method is feeding animals diets rich in omega-3s. This in turn boosts the omega-3 content of the meat/eggs they produce.
 
What omega-3s do for us
The best evidence relating to the benefits of omega-3s is in relation to cardiovascular disease. It has been clearly demonstrated that the consumption of omega-3s after a myocardial infarction (MI) reduces the likelihood of having a further fatal heart attack.(5) However, there is also substantial evidence that omega-3s are beneficial in the primary prevention of heart disease,(1) as they:

  • Prevent thrombosis.
  • Have beneficial effects on blood pressure.
  • Lower blood triglyceride levels.
  • Decrease the risk of heart arrhythmia.

But it is not just our hearts that are likely to benefit from a better intake of omega-3s: there is mounting evidence that these fats are important for other reasons.

Brain development
It is now known that the omega-3 fat DHA is a major structural component of the human brain, and therefore vital for optimal brain development. As there is rapid brain growth in the last three months of fetal life and during infancy, it has been suggested that pregnant and lactating women should be consuming more DHA than other adults.(6 ) However, the Food Standards Agency recommends that pregnant women consume only one portion of oily fish per week,(7) so alternative sources of omega-3s should be considered.

There is also concern that formula-fed infants may be lacking in omega-3s, as infant formula is not yet fortified and few weaning foods contain them. Omega-3-rich eggs are one exception. A recent study found that blood concentrations of DHA were 30-40% higher in infants given omega-3-enriched egg yolks during weaning, compared with those given standard or no eggs.(8)

Inflammatory conditions
Omega-3s have also been found to help inflammatory conditions such as rheumatoid arthritis. Fish oil supplements have been found to reduce morning stiffness and joint pain in arthritis sufferers. By contrast, the intake of omega-6 fats was found to exacerbate the problem.(9) There is also the suggestion that omega-3s may help reduce airway inflammation in asthma sufferers.(10)

Depression
Another interesting possibility is that omega-3 fats may help to keep us happy. It has been found that people from countries with high fish consumption such as Iceland and Japan have low rates of depressive disorders.(11)  Studies have also shown that omega-3s can help depressed patients. For example, Nemets and colleagues recently reported that depressed patients given fish oil supplements showed a highly significant reduction in symptoms such as low mood, insomnia and feeling worthless when compared with a placebo group on medication alone.(12) It is suggested that omega-3s may boost levels of the mood-lifting brain hormone serotonin.
 
Other patients suffering from psychiatric illness may also benefit. Low levels of DHA and EPA have been found in people suffering from diseases such as Alzheimer's disease and dementia. Supplementation with omega-3s may help to improve mood, cooperation, appetite and short-term memory in such patients.(13)

Who will benefit from omega-3s?
Omega-3s have an important role in both human development and the maintenance of good health. This means that everyone from birth through to old age needs an adequate intake. However, there are two groups where there is good evidence that omega-3s are especially important:

  • Pregnant and lactating women - omega-3s are vital to ensure optimum brain development in the baby.
  • People at high risk of cardiovascular disease or post-MI - omega-3s reduce the risk of heart ­disease and the likelihood of a further cardiac event.

Other people who may benefit from boosting their intake of omega-3s include:

  • Young children.
  • Asthmatics.
  • Rheumatoid arthritis sufferers.
  • The elderly.
  • Those suffering from psychiatric illness.

Dietary advice
It is important that general dietary advice encourages the right balance of fats. Most people are not eating enough omega-3 fats at the moment, so they need to be positively encouraged. In particular, weekly consumption of oily fish should be promoted.  It would also be useful to encourage the use of vegetable oils such as walnut and soya oils, and to mention other sources of omega-3s such as fortified breads, spreads and eggs.

Reference

  1. British Nutrition Foundation. n-3 fatty acids and health [briefing paper]. London: BNF; 1999.
  2. Department of Health. National Food Survey 2000. Annual report on food expenditure and consumption. London: The Stationery Office; 2001.
  3. Committee on Medical Aspects of Food & Nutrition Policy. Nutritional aspects of cardiovascular disease [Policy Report on health and social subjects no. 46]. London: Department of Health; 1994.
  4. BMRB. Omnibus survey amongst 377 parents of children aged between 18 months and 10 years. London: BMRB; 2002.
  5. GISSI-Prevenzione. Dietary ­supplementation with n-3 ­polyunsaturated fatty acids and vitamin E after myocardial infarction. Lancet 1999;354:447-55.
  6. Simopoulos AP, Leaf A, Salem N. Workshop on the essentiality of, and recommended dietary intakes for, omega-6 and omega-3 fatty acids. 1999.    Available from URL: http://www.issfal. org.uk/adequateintakes.htm
  7. What is the advice (about fish consumption) for pregnant women? Available from URL: http://www.foodstandards.gov.uk
  8. Makrides M, Hawkes JS, Neumann MA, Gibson RA. Nutritional effect of including egg yolk in the weaning diet of breast-fed and formula-fed infants: a randomised controlled trial. Am J Clin Nutr 2002;75:1084-92.
  9. Darlington LG, Stone TW. Antioxidants and fatty acids in the amelioration of rheumatoid arthritis and related disorders. Br J Nutr 2001;85:251-69.
  10. Hodge L, Salome CM, Peat JK, Haby MM, Xuan W, Woolcock AJ. Consumption of oily fish and childhood asthma risk. Med J Aust 1996;164:137-40.
  11. Tanskenen A, Hibbeln JR, Hintikka J, Haatainen K, Honkalampi K, Vinamaki H. Fish consumption, depression and suicidality in a general population. Arch Gen Psychiatry
  12. Nemets B, Stahl Z, Belmaker MD. Addition of omega-3 fatty acid to ­maintenance medication treatment of recurrent unipolar depressive disorder. Am J Psychiatry 2002;159;477-9.
  13. Conquer JA, Tierney MC, Zecevic J, Bettger WJ, Fischer RH. Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia and cognitive impairment. Lipids 2000:35:1305-12.

Resources
International Society for the Study of Fatty Acids and Lipids
W:www.issfal.org.uk

Food Standards Agency
W:www.foodstandards.gov.uk

World Health Organization Nutrition page
W:www.who.int/nut

Columbus eggs
W:www.columbus eggs.com