Influence of ethnic origin (Asian v. Caucasian) and background diet on the bioavailability of dietary isoflavones.

Soya isoflavones: genistein and daidzein are increasingly consumed in Western countries. Their beneficial effects are discussed considering nutrition and health in Asia. The present study aimed to check whether chronic ingestions, ethnic origin and dietary context can influence soya phyto-oestrogen bioavailability. Two prospective trials were carried out to blindly assess the pharmacokinetics after acute and chronic intake of soya-based cheese (45.97 (sd1.57) mg isoflavones) taken once a day for 10 d. Twelve healthy young Asians immersed for 2 months in France were randomised in a cross-over design to compare the influence of a Western v. Asian dietary context. The second trial partly nested in the first one, compared Asians under the Western diet to twelve healthy young male Caucasians under the same diet. All volunteers were non-equol producers. After an acute intake of soya in Western diet, Asians exhibited higher maximum concentration measured in plasma (Cmax) and area under the plasma concentration-time curve (AUC) for genistein and daidzein than Caucasians (P = 0.005, 0.006, 0.032 and 0.008, respectively). In Caucasians under Western diet, AUC and Cmax values significantly increased after chronic intake. This was not the case for daidzein in Asians whatever the dietary context. For the first time, it is evidenced that on acute intake of soya cheese, Asians absorb soya phyto-oestrogens better than Caucasians, regardless of whether the background diet is Western or Asian. On chronic ingestions, AUC and Cmax values were increased for daidzein and genistein in Caucasians but not in Asians. There are ethnic differences in isoflavone pharmacokinetic and bioavailability. This may influence health outcomes.