Soybeans contain a number of polyphenolic substances that belong to the isoflavone group of phytochemicals. Interest in these phytochemicals has grown as evidence suggests that they may have beneficial health effects. In particular daidzein and genistein are two isoflavones found in soy products that may have beneficial cardioprotective and anti-cancer effects in humans. As more is learnt about these isoflavones, it is becoming apparent that their effects on humans might vary considerably, as biochemical individuality determines how they are digested and absorbed. Daidzein for example, may require conversion to a substance called equol by the bacteria of the gut before absorption, but this process appears to be low or absent in certain individuals. This step is important because one of the ways that the isoflavones in soy may be beneficial is through interaction with the oestrogen receptor, and equol has a higher binding affinity to the oestrogen receptor than either its parent compound daidzein, or genistein.
Isoflavones may therefore have more physiological effects in equol producers compared to non-equol producers. In particular equol may be beneficial at modulating plasma lipoprotein concentrations favourably. However, the effects of isoflavones on plasma lipoproteins also appears to be genetically linked, with polymorphisms in the oestrogen receptor affecting the benefits of the isoflavones on lipoprotein levels. For example, in one study1, researchers evaluated the effects of six months of daidzein supplementation on the cardiometabolic risk factors in in hypercholesterolaemic individuals, using a placebo controlled, double-blind study design. Subjects received either 40 or 80 mg of daidzein per day, while some subjects received a placebo. The results showed that following the six month supplementation period, 40 and 80 mg per day of daidzein decreased serum triglycerides levels by 0.15 mmol/L and 0.24 mmol/L, and uric acid levels by 23 and 29 μmol/L, respectively, when compared to the placebo.
However, interestingly, the reduction in the triglyceride levels seen in the subjects was influenced by the genotype of the subjects. Subjects with a particular polymorphism (GA versus GG genotype) in the oestrogen receptor beta (ESR-β) had significantly greater reductions in plasma triglycerides in response to daidzein supplementation. Therefore the GA genotype in the oestrogen receptor beta appears to be the defining factor in the efficacy of daidzein at lowering plasma triglycerides and not the conversion to equol. Other studies have found that daidzein lowers triglycerides in humans, with a meta-analysis showing daidzein supplements and soy with its daidzein content intact significantly lowers plasma triglyceride levels in humans, with the effects being more pronounced in those with hypertriglyceridaemia. The ability of daidzein to lower plasma levels of uric acid, may relate to the influence of the isoflavone on xanthine oxidase, the enzyme responsible for uric acid production. Studies in rats show that daidzein is able to inhibit xanthine oxidase, perhaps making it a useful treatment for hyperuricaemia.
Dr Robert Barrington’s Nutritional Recommendation: In this study the authors noted that more women were equol producers compared to men (64 versus 56.7 %, respectively). This supports previous data from other studies performed on Chinese subjects (this study was performed in China). However, in this study, the ability to produce equol from bacterial fermentation was not a requirement for the beneficial effects on triglyceride or uric acid levels. Subjects who do not produce equol may still therefore benefit from soy isoflavone supplements. Supplements of isoflavones, whole soybeans and soy protein all appear to show beneficial effects. Individuals with hyeruricaemia may benefit from daidzein supplements because of its inhibitory effects on xanthine oxidase.
RdB
