Spilling the beans

Millions of us eat soya to help lower cholesterol, ease menopausal symptoms and protect against cancers. But not all doctors are convinced of its benefits - or its safety, says Jane Feinmann

Should the nutritious soya bean, said to have kept Asia healthy for 3,000 years, be part of a healthy Western diet? The high-protein, high-antioxidant bean, for decades a favourite meat alternative for vegetarians, is on the way to becoming a truly populist health food. But it's not just celebrities such as Carol Vorderman and Geri Halliwell who love soya. Sampled at least once by one in two of the population, it is widely consumed by millions as part of their daily diet.

Should the nutritious soya bean, said to have kept Asia healthy for 3,000 years, be part of a healthy Western diet? The high-protein, high-antioxidant bean, for decades a favourite meat alternative for vegetarians, is on the way to becoming a truly populist health food. But it's not just celebrities such as Carol Vorderman and Geri Halliwell who love soya. Sampled at least once by one in two of the population, it is widely consumed by millions as part of their daily diet.

Serious clinical interest in soya began with its potential to control menopausal symptoms - following the epidemiological observation made in the Eighties, that the soya-loving Japanese have no word for hot flushes. The arrival of decent-tasting soya milk and yoghurt in supermarkets made it a must-buy - and not just for women or the lactose intolerant.

By 1999, the American Food and Drug Administration (FDA) was persuaded by the research evidence to approve an "unqualified" (ie irrefutable) health claim that soya protein contributes to a reduction in the risk of coronary heart disease by lowering cholesterol levels. This claim, available to manufacturers to use on their products, was subsequently rubber-stamped by an independent UK authority (the Joint Health Claims Initiative). And it's not just heart disease. The FDA was due to report on a three-year consultation on whether products can carry health claims on the role of soya in reducing the risk of breast, colon and prostate cancer.

Yet at the same time serious concerns are surfacing about soya's potentially adverse effects. Most alarming is an abstract appearing in the November issue of the British Journal of Obstetrics and Gynaecology of an unpublished study, claiming to show that a central component of soya, a phyto-oestrogen called genistein, is associated with infertility in men.

Professor Neil McClure, a fertility specialist at Belfast Royal Infirmary, inspected the sperm of 24 men whose partners were having difficulty in conceiving and identified "significantly higher" levels of genistein. This led him to conclude that soya is "associated with impaired sperm function".

Other anxieties include soya's potential to cause thyroid problems, abnormal brain development in babies, and breast cancer. There are reports of scientists' concerns being ignored and suggestions that the authorities in America and the UK have been nobbled by the multi-billion dollar US soya industry, to sweep such concerns under the carpet.

Yet experts on both side of the Atlantic make it clear that the issue of whether soya is a potentially toxic or health-promoting substance is problematic. Take the recent study on genistein and sperm impairment. It may appear that the results belonged to men who were soya consumers. But that is almost certainly not the case. Professor McClure admits that his subjects were not asked about soya consumption and that "as soya milk doesn't tend to be very popular in Northern Ireland, they were unlikely to have deliberately consumed soya". He points out that as soya is "ubiquitous" in processed and fast foods, "eating too many hamburgers can significantly raise genistein levels".

But such a claim has little if any scientific basis, according to Aedin Cassidy, Professor of Diet and Health at the University of East Anglia School of Medicine. She says that research studies since the Eighties have shown that a daily intake of around 45mg of soya (about two glasses) is required to bring about any hormonal change.

"There is no effect whatsoever with even 25mg. And it's virtually impossible to consume more than 2mg of soya daily in processed food. A problem with soya is that isoflavones are also called phyto-oestrogens - and therefore seen to share properties with the Pill and HRT," says Professor Cassidy.

"Isoflavones such as genistein do affect oestrogen status in healthy young women, lengthening the menstrual cycle - which probably explains why women in soya-eating populations are less likely to develop breast cancer. But they don't have an oestrogenic effect on men - there is no evidence of reduced fertility in Asian countries where soya has been a mainstay of diet for thousands of years," she adds.

There is also confusion over soya's impact on cholesterol. Even soya enthusiasts acknowledge that the FDA's 1999 advice, based on research showing the cholesterol-reducing impact of soya protein, may well have been overstated. "We now believe that soya protein lowers cholesterol about five per cent beyond the effect of a low-fat diet," says Dr Mark Messina, author of The Simple Soybean and Your Health, and Professor of Nutrition at Lorna Linda University, California. "This is a clinically relevant benefit but it is lower than the 13 per cent reduction initially attributed to soya protein."

While some studies suggest that soya protects against cancer, others show it as causing the disease - though Cancer Research UK and the International Prostate Health Council are two bodies reporting health benefits. And research suggests that there is a question mark over whether soya is of benefit for menopausal symptoms.

According to Professor Cassidy, the problem with soya, "is that isoflavone supplements don't seem to work on their own. You need the whole food and comparing like with like in food research is notoriously difficult." What's more, the whole food itself is difficult to pin down. "Soya oil doesn't contain protein or isoflavones and most soya meat substitutes, while high in soya protein, are usually very low in isoflavones. Only soya milk is both protein and isoflavone rich," says Dr Messina.

Two EU-funded trials are under way to test the impact of soya on preventing heart disease and osteoporosis. "We need to provide the evidence to allow people to make a truly informed decision about soya," says Professor Cassidy.

DO YOU KNOW WHAT'S GOOD FOR YOU?

Organic food : A survey in October (by The Sunday Times) showed that some supermarket organic products, including milk, meat and soup, have higher levels of fat and salt than conventionally produced counterparts. Tesco, one of the offenders, says: "We have never positioned our organic brand as being a healthy product. Our customers understand it relates to a production method. The difference in salt and fat is due to the different recipes we use."

Wholemeal bread: A Which? survey in June found that wholemeal bread in some supermarkets had more fat than a bar of chocolate - double the fat of white bread - and lower in calcium and added vitamins. "Even so, wholemeal is a healthy option - the fat is unsaturated and it is a rich source of fibre," says Dr Anne Nugent of the British Nutrition Foundation.

Eggs: After years of being considered a dangerous source of cholesterol, eggs are widely considered highly nutritious food - three to four eggs a week are part of a balanced diet, says the British Heart Foundation. There's no evidence that either organic eggs or omega-3, rich Columbus eggs are any better for you - but only because no one has checked.

Milk: With up to one in two of the population believing they are lactose intolerant and an influential platform claiming that cow's milk promotes hormone-related cancers, milk has lost some of its healthy glow. That should not put people off, warns Dr Nugent, especially in adolescence. "It's an excellent, nutritious food which, as semi-skimmed, is low-fat," she says.