Sir
Recent media coverage has questioned the safety of soya for fertility and has led to concern about women eating soya foods if they are trying to conceive.
To date, there is no conclusive evidence that soya, when eaten as part of a healthy balanced diet, has any effect on fertility. In fact, its safety has been extensively reviewed, including by the UK Committee on Toxicity, the Expert Committee of the Joint Health Claims Initiative and the US Food and Drug Administration.
The current scare followed a presentation given by Professor Lynn Fraser of King's College, London, who told the 21st conference of the European Society of Human Reproduction and Embryology in Copenhagen that her research had shown combinations of chemicals found in everyday products had subtle but potentially damaging effects on sperm fertility.
Fraser tested the effects of various chemicals including genistein (a type of isoflavone found in legumes and soya), on capacitation, which is the stage when sperm acquires the ability to fertilise an egg. She did this as a piece of isolated laboratory research on a small amount of human sperm in vitro, following earlier research on mice sperm.
Various reports and recommendations extrapolated data from research in the laboratory to what might happen in everyday human biology. This is a giant leap from what we know. There is no proof that this is what actually happens in the human body.
Fraser used the isolated and pure isoflavone compound genistein. This is not the same form you find in the body after the consumption of soya foods. The human body quickly metabolises genistein into a different form, so direct comparisons cannot be made.
Dominic Dyer
Executive director
Soya Protein Association