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The health benefits of eating foods containing omega-3 fatty acids

Dr Judy Buttriss, PhD, SRD, RPHNutr.

Science Director, British Nutrition Foundation, London

This paper discusses the benefits to be gained from omega-3 fatty acids and suggests ways in which nurses can help patients ensure they are receiving an adequate intake. 'Omega-3' has become one of the recent buzzwords in nutrition. This paper looks at what omega-3s are and why they are important.

This paper discusses the benefits to be gained from omega-3 fatty acids and suggests ways in which nurses can help patients ensure they are receiving an adequate intake. 'Omega-3' has become one of the recent buzzwords in nutrition. This paper looks at what omega-3s are and why they are important.

Omega-3s, like all fatty acids, are building blocks from which lipids (fats) are made. Fatty acids may be saturated, monounsaturated or, like omega-3s, polyunsaturated. There are two families of polyunsaturated fatty acids:

- The omega-6 or (n-6) family, which is derived from linoleic acid (LA), an essential fatty acid.

- The omega-3 (or n-3) family, derived from alpha-linolenic acid (ALA), an essential fatty acid.

The fatty acids in these two families, which are essential to the development and maintenance of a healthy body, are termed 'essential' because they cannot be made in the body and so must be provided by the diet. In the body, ALA can be converted to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are known as long-chain fatty acids, and they also provide important health benefits. Although these can be synthesised in the body from ALA, dietary sources remain important because the conversion process seems to be inefficient in some individuals (BNF, 1992). While the individual levels of omega-3 and omega-6 acids are important, it is the balance between the two that is currently receiving the most attention. The two families of fatty acids interact metabolically, and a shift in the ratio may influence the types and potency of the EPA and DHA derivatives formed.

The benefits of omega-3s
Omega-3s have a range of benefits for both healthy development and protection against disease (Box 1).

Growth and development - Long-chain polyunsaturated fatty acids (both omega-6 and omega-3) are essential for the formation of new tissues. Omega-3 fatty acids (particularly DHA) are particularly important for the development of the retinal and nervous tissue, including the brain.

During the last three months of pregnancy, omega-3 fatty acids accumulate rapidly in these tissues. In preterm babies in particular, the rate of synthesis of long-chain omega-3s from ALA may be inadequate for optimal growth. For this reason, it has been suggested that it may be useful to enrich infant formula milks with long-chain omega-3s. DHA is present in breast milk, but historically has not been added to infant formula, although an EU directive now permits its addition (The Stationery Office, 1997).

Heart disease and other chronic disease - Although omega-3 fatty acids have little or no effect on total blood cholesterol levels, a substantial amount of recent work has focused on their ability to reduce blood triglyceride levels (a risk factor for cardiovascular disease), both in the fasting state and following a meal (BNF, 1999). This, together with evidence that long-chain omega-3s reduce the risk of fatal heart attacks (BNF, 1999), indicates an important role for omega-3s in maintaining heart health.

A recent trial confirmed that 1g of EPA and DHA each day reduced the risk of dying from a heart attack - in those who had suffered a previous heart attack - by 20% (GISSI-Prevenzione Investigators, 1999). Similar results had been obtained previously in a British study using oil-rich fish (Burr et al, 1989). It has been proposed that this result may be due to protection against blood-clot formation (thrombosis) and heart arrhythmia (BNF, 1999) or to a beneficial effect on blood pressure (BNF, 1999). Links have also been proposed between omega-3 fatty acid intake and improved insulin sensitivity, which is important with regard to diabetes (BNF, 1999).

Depression and Alzheimer's disease - Work in this area remains highly speculative, but there is a limited amount of data hinting that either a poor intake of omega-3s or an imbalance between omega-3 and omega-6 fatty acids might be associated with various manifestations of impaired cognitive function (BNF, 1999). For example, low levels of omega-3 fatty acids have been reported in cell membranes of subjects with depression, schizophrenia and Alzheimer's disease (BNF, 1999), but it remains to be shown whether this association is causal, or simply reflects changes in the dietary pattern that have resulted from the illness.

Inflammatory conditions - Both long-chain omega-3 and long-chain omega-6 fatty acids participate indirectly in inflammatory and immune responses, and may either dampen or heighten responses. Because omega-3s tend to be anti-inflammatory, it has been speculated that a lower dietary omega-6 to omega-3 ratio might be beneficial in various conditions involving an abnormal immune response (BNF, 1992). Use of fish-oil supplements has become popular for the treatment of conditions such as rheumatoid arthritis. Some patients report relief of symptoms but the proven clinical benefit is modest and the long-term benefits and disadvantages need further evaluation (BNF, 1999).

Food sources of omega-3s
Table 1 lists sources of omega-3s. The pre-formed, long-chain omega-3 fatty acids - DHA and EPA - are found in abundance in fish oils, and in the flesh of oil-rich fish, such as mackerel, salmon, kippers, herrings, sprats, trout, sardines and pilchards - whether fresh or tinned. Tinned tuna is not a good source, however, although fresh tuna does provide moderate amounts.

The richest dietary sources of alpha-linolenic acid are some seed oils such as linseed oil, rapeseed oil, soya oil, and mustard oil, and some nuts, in particular walnuts. Meat, meat products and cereal products are also quantitatively important sources. There is also some ALA present in green leafy vegetables.

It is evident from this list that the range of foods providing omega-3s is relatively small. For some time, fish-oil supplements have been available for those who wish to use them. For those who prefer to obtain their nutrients from foods, a number of omega-3 fortified products have been introduced to the market, including enriched spreads, cereal products and omega-3-enriched eggs (Columbus eggs). These eggs are produced by enriching the hens' diet with omega-3 fatty acids. Typically, a two-egg portion contains approximately 0.3g of long-chain omega-3s and, in total, 1.6g of omega-3s. By comparison, a serving of oil-rich fish typically provides between 1.7 and 3.4g EPA and DHA.

Recommendations for patients
Patients need to understand the benefits associated with omega-3 fatty acids, as well as the best nutritional sources of them. Despite Department of Health (1994) recommendations to eat at least two servings of fish a week, one of which should be oil-rich fish, for many people this advice is not a readily accepted means of consuming omega-3 fatty acids. The development of omega-3 fortified products will go some way in meeting this need.

Pregnant women need to be aware of the importance of eating foods rich in omega-3s. This will ensure the developing baby has access to adequate amounts while in the womb, and later via the breast milk, should the woman choose to breast-feed. There is evidence that levels of omega-3s in the mother's blood fall during pregnancy, and if pregnancies are closely spaced, levels may not have time to recover (Al et al, 1995). This emphasises the importance of good eating habits post-pregnancy as well as during pregnancy itself.

Conclusion
It is now recognised that an adequate intake of omega-3 fatty acids is important for human health. In particular, several biological roles have been identified for the long-chain omega-3s EPA and DHA, present in oil-rich fish. Many patients are reluctant to increase their intakes of this type of food. However, through education, nurses can offer alternative dietary strategies to enable their patients to meet the recommendations for a healthy diet.

Recommendations for nursing practice
- Nurses can usefully remind patients and clients about the importance of including oil-rich fish in the diet. For those patients who do not like this type of fish, alternatives can be suggested, using the information in Table 1.

- Particular groups to target with this advice are those at risk of heart disease, for whom the evidence is most robust. It is also relevant to pregnant and nursing mothers and people with rheumatoid arthritis, although in relation to the latter most of the evidence concerns fish-oil supplements rather than foods.

Al, M.N.M., van Houwelingen, A.C., Kester, A.D.M. et al. (1995) Maternal essential fatty acid patterns during normal pregnancy and its relationship with the neonatal essential fatty acid status. British Journal of Nutrition 74: 55-68.

British Nutrition Foundation. (1992)Unsaturated Fatty Acids: Nutritional and physiological significance (Report of the British Nutrition Foundation's Task Force). London: Chapman and Hall.

British Nutrition Foundation. (1999)n-3 Fatty Acids and Health (Briefing Paper). London: British Nutrition Foundation.

Burr, M.L., Fehily, A.M., Gilbert, J.F. (1989)Effects of changes in fat, fish and fibre intakes on death and myocardial infarction: Diet and Reinfarction Trial (DART). Lancet 2: 757-761.

Department of Health. (1994)Nutritional Aspects of Cardiovascular Disease (Report on Health and Social Subjects 46). London: The Stationery Office.

GISSI-Prevenzione Investigators. (1999)Dietary supplementation with n-3 fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione Trial. Lancet 354: 447-455.

The Stationery Office. (1997)Statutory Instrument. The Infant Formula and Follow-on Formula (Amendment) Regulations. London: The Stationery Office.

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