Nineteen of 25 dietary supplements containing the essential fatty acids ALA (alpha-linolenic acid) and GLA (gamma-linolenic acid) passed an assessment by the independent product evaluator ConsumerLab.com.
GLA is an omega-6 fatty acid and is used to alleviate pain and inflammation, while ALA is an omega-3 fatty acid like those found in fish oils and can be used to make other omega-3 fatty acids EPA and DHA.
The products tested by ConsumerLab.com were made from blackcurrant, borage, evening primrose and flaxseed oils. The organisation has already assessed fish oil supplements as a source of essential fatty acids.
Flaxseed contains the highest levels of ALA - some 55 per cent of the oil contains the fatty acid - while hemp contains 19 per cent and blackcurrant 13 per cent. Soybean, canola and walnut oils also contain lower concentrations of the fatty acid.
The body has a limited ability to manufacture both EPA and DHA from ALA (only about 10 per cent is converted), and this is lessened if the diet is too high in omega-6 fatty acids, because they compete with omega-3 fatty acids for certain enzymes as they are metabolised.
In contrast, the body is usually able to produce sufficient levels of GLA from linoleic acid (LA) which is found in corn, sunflower, safflower, soy, peanut and flaxseed oils, among others. However, supplementation with the fatty acid is recommended in cases such as old age, high alcohol intake or elevated cholesterol. Blackcurrant, borage and evening primrose are among the few oil seeds which are rich in GLA, said ConsumerLab.com.
"Because omega-3 fatty acids are obtained from natural sources, levels in supplements can vary, depending on the source and method of processing. The freshness of the oil is also an important consideration because rancid oils have an unpleasant taste, odour, can cause gastrointestinal side- effects and may not be as effective due to degradation. In addition, rancid fat contains chemicals called peroxides and aldehydes that can damage cells and may even encourage cholesterol to clog arteries. Neither the FDA nor any other federal or state agency routinely tests fish or marine oil supplements for quality prior to sale," ConsumerLab.com explained.
The organisation tested a variety of products which claimed to contain ALA, GLA, LA or related seed oils for signs of decomposition and assessed whether their levels of these and other omega-3 or omega-6 fatty acids matched those claimed on the labels.
Of the 25 supplements tested, 11 were evening primrose oil products, nine were flaxseed oil products, two were blackcurrant oil products, two were borage oil products, and one was a combination of evening primrose and borage oils. Products were either in softgel or liquid form.
Six of the 25 products failed to pass the review. While none of these were low in ALA or GLA, four flaxseed products had only 70 to 83 per cent of their claimed amounts of linoleic acid. Two other products - one made of evening primrose and the other of borage oil, had high peroxide values, indicating that spoilage (rancidity) was occurring. Rancid products are less palatable and may cause increased gastrointestinal side effects.
As polyunsaturated fats, essential fatty acids are extremely susceptible to spoilage by oxidation. Vitamin E is often added to essential fatty acid products, because of its antioxidant properties. However, this is apparently no guarantee of freshness, since vitamin E was listed as an ingredient in the failed borage oil product; Nor is it a requirement for freshness, since the majority of products that passed did not contain an antioxidant.
The complete list of products which passed the test can be found on the ConsumerLab.com website, including products from Vitamin World, Nature's Bounty and Puritan's Pride.