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Getting omega-3s the vegetarian way

Julia Wolman
MSc BSc(Hons) RPHNutr
Registered Public Health Nutritionist
London

Not all fats are bad. Omega-3 is a type of good fat, and its importance for optimum physical and mental health is becoming increasingly recognised. Now being added to a growing range of everyday foods, omega-3s have never been more of a hot topic.

What is omega-3?
Fat in the diet can be categorised as either saturated, commonly known as "bad" fat, and unsaturated, or "good" fat. Unsaturated fat can be either monounsaturated (found in foods such as olive oil, nuts and avocados) or polyunsaturated (eg, in sunflower oil) (see Figure 1). Polyunsaturated fats can be further subdivided into omega-3, such as alpha-linolenic acid (ALA), and omega-6 fat, such as linoleic acid (LA). Both ALA and LA must come from the diet as they cannot be produced by the body. As such, they are both known as essential fatty acids. ALA is not more beneficial than LA - they are both essential - but we have a greater consumption of LA, often at the expense of ALA.

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Long-chain omega-3 fats
Omega-3 fatty acids can be either short- or long-chain, according to their chemical structure. ALA is a short-chain omega-3 fat and is a precursor of the long-chain omega-3 fats eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are currently attracting all the attention - they are the fatty acids found in oily fish.
Although ALA, EPA and DHA are all beneficial to health, the latter two long-chain fatty acids exert more beneficial effects than their short-chain precursor ALA, which is found in plant foods. The good news for vegetarians is that ALA can be converted by the body into EPA and DHA. Unfortunately, however, this conversion process can be inefficient, being hindered by factors such as high omega-6 intake.

Benefits of omega-3
The long chain omega-3 fats are recognised for their cardioprotective properties, helping the heart to beat more regularly, reducing the stickiness of the blood and reducing the risk of clotting. Data from the Nurses' Health Study found that those with a higher intake of long-chain omega-3 fatty acids had a lower risk of coronary heart disease, especially a lower risk of death from the disease.(2)
Long-chain omega-3s may also have a potentially beneficial role in arthritis and other joint problems due to their anti-inflammatory effects, not to mention their importance for nerve growth, brain structure, cognitive function and retinal development, especially for the developing fetus.(3)

Omega-3 and obesity
Evidence for the role of omega-3 fats in weight control is limited. However, the International Cod Liver Omega-3 Foundation suggests that "the long chain omega-3 polyunsaturates can aid weight loss by enabling each of the body's cells to function in the optimal manner". Recent reports on 75 overweight or obese adults in a double-blind trial found that those who received a daily supplement of long-chain omega-3 fatty acids, combined with a moderate-exercise regime, showed a significant reduction in percentage body fat. Interestingly, no other changes to eating habits were made. Possible mechanisms are thought to be enhanced fat oxidation during exercise and improved blood flow in exercising muscles.(4)

Omega-3 deficiency
In the UK, the intake of the omega-6 fat (LA) is typically far greater than the omega-3 (ALA) type. In fact, it is suggested that over the past century our intakes of omega-3s have decreased, while at the same time omega-6 intakes have increased. LA is widely available in both vegetarian and nonvegetarian diets, being found in commonly used oils, such as sunflower, as well as many processed foods, whereas ALA is generally less widely available. As a result, the British diet currently provides LA and ALA in the ratio of 7:1, far from the 1.5:1 recommended. As mentioned above, high LA intakes may hinder the conversion process for ALA to the longer-chain EPA and DHA, as both the omega-6 and omega-3 families compete for enzymes in their metabolic pathways.(5)
Although not an established clinical condition as such, fatty acid deficiency, or an imbalance of omega-3 or omega-6 fats, may be indicated by a range of physical and emotional symptoms that practitioners should be aware of (see Table 1).(6)

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How much omega-3?
It is recommended that average consumption of long-chain polyunsaturated fatty acids should be increased from about 0.2g to 0.45g a day.(7) For the nonvegetarian, oily fish is the best source of long-chain omega-3s that the body can readily use. The public health message to consume two portions of fish a week, one of which should be oily, would provide the equivalent of about 0.45g of long-chain omega-3 per day, hence meeting the recommendation. The International Society for the Study of Fatty Acids and Lipids recommends a minimum of 0.3g a day during pregnancy and lactation.(8)

Omega-3 and the vegetarian diet
Vegetarian diets generally do not contain much EPA or DHA, so vegetarians must instead rely on the conversion of ALA from plant foods, one of the best sources being flaxseed (linseed) oil (see Table 2). The Vegetarian Society of the UK suggests an intake of approximately 4g of ALA a day, which can be obtained from just one teaspoon of flaxseed (linseed) oil (cold), four to five teaspoons of ground or crushed flaxseeds (linseeds), two to three tablespoons of cold rapeseed (canola) oil, or about six or seven walnuts.(9)

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It is advisable for vegetarians to limit their intake of LA from, say, sunflower or corn oil, as high consumption could interfere with the conversion process of ALA into the more beneficial EPA and DHA, as discussed above. One practical strategy could be to replace sunflower oil with olive oil, as the monounsaturated fat in olive oil does not interfere with the ALA conversion process. See Box 1 for more practical advice for vegetarians.

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Fortified foods
The food industry is developing an increasing (and often costly) range of everyday foods artificially fortified with omega-3 - for example, yoghurts, fruit juices, margarine spreads, milks and eggs. Some manufacturers use omega-3 derived from fish oils, so vegetarians should be sure to check food labels before they buy.

Omega-3 supplements
A wide range of supplements are available, all containing varying degrees of omega-3. There are no recommendations for omega-3 supplements; their use is largely down to personal choice. Where children are concerned, if parents or carers do choose to give a supplement, they should check the label to ensure it is designed for the appropriate age group.
Consuming two portions of fish, one being oily, each week should provide sufficient long-chain omega-3 fatty acids from the diet alone. However, vegetarians who are concerned they may not be getting enough omega-3 from food may consider taking omega-3 ALA supplements, usually derived from flaxseed (linseed) oil (although there is no specific recommendation to do so). Algae-based DHA supplements are also available, although not widely, and may be a better source of the beneficial long-chain omega-3 for vegetarians.
Research has suggested that adequate maternal intakes of long-chain omega-3 fatty acids have cognitive and behavioural benefits for the child - for example, better language development and attention levels.(10,11) This, in addition to the role of omega-3 fats in fetal development, highlights a potential place for supplements of long-chain omega-3 for vegetarian women planning a pregnancy, or who are pregnant or breastfeeding. Increasing fish consumption beyond two servings of oil-rich fish per week or relying on fish oil supplementation is not appropriate during pregnancy due to the potential problems associated with heavy metal contamination of fish and the high vitamin A levels in some fish oil supplements.
Consumers often consider nutritional supplements as a magic bullet and an easy way to achieve good health. However, health professionals should not promote supplements as a substitute for a healthy, balanced diet.

Conclusion
The evidence suggests that the population as a whole would benefit from increased omega-3 intakes, especially the long-chain varieties.5 For the nonvegetarian this can be easily achieved by the regular consumption of fish, especially oily fish. For the vegetarian, however, careful attention is needed to adapt the diet to include sufficient sources of the parent short-chain omega-3 fatty acid ALA.
An ever-increasing range of omega-3-enriched foods and supplements is now widely available, and no doubt manufacturers will continue to develop products in line with this trend. These may make a useful contribution for the vegetarian. However, emphasis should be placed on the inclusion of natural plant food sources of ALA into the vegetarian diet, while also reducing consumption of the omega-6 fat LA, to optimise intake and balance of the essential fats so as to achieve good health without fish.

References

  1. Scientific Advisory Committee on Nutrition/ Committee on Toxicity. Advice on fish consumption: benefits and risks. London: The Stationery Office; 2004.
  2. Hu F, Bronner L, Willett W, et al. Fish and omega-3 fatty acid intake and risk of coronary heart disease in women. JAMA 2002;287:1815-21.
  3. Al M, Houwelingene A, Hornstra G. Long chain polyunsaturated fatty acids, pregnancy and pregnancy outcome. Am J Clin Nutr 1995;71:S285-91.
  4. Hill A. Running on fish oil: benefits of omega-3 supplementation and exercise. ISSFAL Congress, Cairns, Australia. 2006. Available from:
    http://www.dhaomega3.org/News/ISSFAL_07_25.pdf
  5. Lunn J, Theobald H. The health effects of dietary unsaturated fatty acids. Nutr Bull 2006;31:178-224.
  6. Richardson A, Ross M. Physical signs of fatty acid deficiency. FAB Research Factsheet 002. Inverness:Food and Behvaiour; 2003. Available from: http://www.fabresearch.org
  7. SACN/COT (Scientific Advisory Committee on Nutrition/Committeeon Toxicity). Advice on fish consumption: benefits and risks. London: TSO; 2004.
  8. Simopoulos A, Leaf A, Salem N. Workshop on the essentiality of and recommended dietary intakes for omega-6 and omega-3 fatty acids. ISSFAL; 1999. Available from:
    http://www.issfal.org.uk/adequate-intakes.html
  9. The Vegetarian Society. Omega 3 fats: information sheet. Available from: http://www.vegsoc.org/info/omega3.html
  10. Daniels J, Longnecker M, Rowland A, Golding J. Fish intake during pregnancy and early cognitive development of offspring. Epidemiology 2004;15:394-402.
  11. Colombo J, Kannass K, Shaddy D, et al. Maternal DHA and the development of attention in infancy and toddlerhood. Child Dev 2004;75:1254-67.


Resources

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

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

International Cod Liver Omega-3 Foundation
W: www.clo3.com

DHA/EPA Omega-3 Institute
W: www.dhaomega3.com

Vegetarian & Vegan Foundation
W: www.vegetarian.org.uk

The Vegetarian Society
W: www.vegsoc.org

Food and Behaviour Research
W: www.fabresearch.org