The flax plant produces seeds that contain high levels of n-3 fatty acids in the form of α-linolenic acid (ALA, C18:3 (n-3)). Around 55% of the fatty acids by weight in flax seed oil are ALA. The benefits of the n-3 fatty acids from fish oils have been thoroughly reported, and results from epidemiology as well as clinical trials attest to the cardioprotective effects of the long chain n-3 polyunsaturated fatty acids, eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)). However, the conversion of ALA to EPA and DHA in humans is not efficient (reported as 0.2 to 8%, 0.13-6% and <0.5%) and as a result the benefits of supplementing with flax seed oil have been questioned. However, flax contains substances other than n-3 fatty acids that may be beneficial to certain health conditions, particularly blood sugar disorders such as hyperglycaemia, hyperinsulinaemia and diabetes.
Flax is good source of dietary fibre and minerals and contains a lignan called secoisolariciresinol diglucoside (SDG), and therefore researchers are interested in its benefits to blood sugar disorders. In a randomised controlled trial1, 34 diabetic subjects were fed either bakery products containing no flax (the control), bakery products containing milled flax seeds (32g/d) or bakery products containing flax oil (13g/d), for 12 weeks. Plasma phospholipid n-3 concentrations increased in the flax oil and flax seed supplemented groups as might be expected, which included elevated levels of ALA and EPA, but not DHA. Of these two groups, EPA increased more in the flax oil group when compared to the flax seed group, although both products contained 7.4g/d of ALA. The bakery products caused a 4kg weight gain in the control group, that was not seen in the flax groups, suggesting that flax may prevent weight gain.
Although the glycaemic control of the subjects was not improved by flax seed or flax oil, these data show that n-3 fatty acid profiles in plasma phospholipids can be improved with ALA supplementation. Previous studies have shown that flax oil is less effective at raising plasma levels of n-3 fatty acid than fish oil, suggesting that the desaturase deficiency in humans that prevents this process is widespread amongst the population. This study may therefore have been more informative if a positive fish oil control was performed. Because flax was incorporated into baked good, the real benefits of the flax seeds on glycaemic control may have been masked by the negative effects of the high carbohydrate foods that caused a 4kg weight gain in the control group. Incorporation of flax into a healthy diet devoid of refined carbohydrates may produce more beneficial results.
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