Do Soy Foods Increase Your Risk of Cancer?

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A: Research linking soy to cancer is limited and has been done on animals.

Experts recommend 1-2 servings of soy a day as part of a balanced diet.

Our expert: Associate Professor Tim Crowe & Dr Kellie Bilinski

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Soy has been a staple in Asian diets for thousands of years, w hile for vegetarians and people w ith lactose intolerance it's a good source of calcium and protein.

W hen you think of soy you probably think of tofu, soy milk and other dairy replacements, edamame, miso, soy sauce and tempeh. But according to the CSIRO, up to 60 per cent of foods in the supermarket contain soybean, including breads, flours, oils, tuna, coffee and sausages.

W hile you tend to find many soy products in the health food aisle, soy's role in a healthy diet has been questioned over recent years and a quick internet search w ill find plenty of w arnings about the dangers of soy – especially after it w as linked to an increased risk of breast cancer.

But research has also found soy may actually help prevent breast cancer, along w ith stomach and prostate cancers, and heart disease. And dietitans, the Cancer Council and our national dietary guidelines still recommend w e eat moderate amounts as part of a healthy diet.

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So w hat should w e believe?

Breast cancer link Soy contains large amounts of phyto-oestrogens (or isoflavones) called genestein and daidzein, w hich are plant chemicals that mimic the hormone oestrogen, although on a much w eaker scale.

One risk factor for breast cancer is high levels of oestrogen and concerns w ere raised w hen research found these phyto-oestrogens increased the risk of the cancer in rats.

But the problem w ith animal studies, explains dietitan and breast cancer researcher Dr Kellie Bilinski, is that rats have very different metabolisms to humans.

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"So you really can't extrapolate those study results to humans," she says. "Plus, these rats w ere given huge doses that w e'd never actually consume."

Related Topics No studies on humans have found that eating soy as part of a healthy diet can be harmful. In fact, research on Asian w omen has found phyto-oestrogens actually have a protective effect against breast cancer.

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"They can help to protect the cells in the body against its ow n oestrogen," explains Tim Crow e, associate professor in nutrition at Deakin University.

"Studies have found the critical stage is during adolescence w hen a w oman's breast is developing, w hich is w hy Asian w omen seem to have low er rates of breast cancer. But w e don't have that same level of consumption in the West."

Cancer Council says although the science on soy being protective against cancer is still inconclusive, it encourages people to eat soy-based foods "as part of a varied and nutritious diet".

"If there's going to be an adverse effect of phyto-oestrogens on hormone-sensitive tumours, it'd be at high concentrations – a lot higher than you'd find in food," Cancer Council CEO Professor Ian Olver says.

"So if people enjoy soy, there's no evidence saying you can't eat it in moderation."

Warning on soy supplements Some of the confusion about soy stems from concerns around isoflavone supplements, w hich may cause problems for w omen w ith a particular type of breast cancer called oestrogen receptor positive.

Women w ho have this type of breast cancer usually receive a treatment called tamoxifen. There's some evidence to suggest that in high doses, like those found in supplements, phyto-oestrogens may actually reduce the drug's effect and promote cancer grow th.

Cancer Council advises men and w omen against taking these supplements for preventing cancer and for breast-cancer sufferers to have soy foods in moderation.

Olver says w hile it's technically possible to get supplement-type dosages from soy foods, it's highly

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unlikely because people w ould need to eat such massive amounts.

Nevertheless, soy is still a healthy food that doesn't need to be avoided by anyone, Bilinski says.

"It's absolutely fine to have a few serves of soy foods a day. These natural phyto-oestrogens are antioxidants and w e should be eating more of them."

Other cancer links Some studies have also suggested soy may low er the risk of prostate and stomach cancers, although Cancer Council says the research is limited.

Phyto-oestrogens have also been linked to an increased risk of endometrial cancer in perimenopausal or post-menopausal w omen, but Cancer Council states "the evidence overall is inadequate to draw conclusions".

Its position statement says any evidence linking soy to pharynx, oesophagus, pancreas, breast, bow el and endometrium cancer is limited w ith no conclusion possible.

"For most cancers there just simply isn't evidence one w ay or the other," Olver explains.

"It's a mistake to focus on one disease and ignore others such as cardiovascular disease and diabetes, w here a product may be quite beneficial."

Health benefits of soy If you like to make tofu stir-fry for dinner or enjoy eating Japanese food, you'll be happy to hear that one to tw o servings of natural soy foods per day have been show n to low er cholesterol.

Soy is also high in protein, fibre, iron and omega-3 fatty acids, and low in saturated fat.

"For vegetarians and people w ho don't eat a lot of red meat – and w e encourage everyone to decrease their intake – it's such a good food," Bilinski says.

"And if you don't eat dairy, soy can be a really good source of calcium as w ell."

Crow e recommends including good-quality soy milk, tofu, miso, edamame and tempeh into your diet.

Although it is w orth noting some popular soy-based foods – such as miso and soy sauce – are very high in sodium and you shouldn't have too much of these.

"Soy foods don't just contain isoflavones, they also contain hundreds of other beneficial chemicals for our health," he says.

"And if you're eating a fair amount of these foods, then you're probably putting less chips and pies in your mouth – and that's going to be good for your health."

Associate Professor Tim Crowe is from Deakin University's School of Exercise and Nutrition Sciences; Dr Kellie Bilinksi is an accredited practicing dietitian and spokesperson for the Dietitians Association of Australia; Professor Ian Olver is the CEO of Cancer Council. They spoke to Cassie W hite.

Published 02/06/2014

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MP :

05 Jun 2014 4:47:07pm

I think w e really should differentiate betw een organic soy products and soy protein isolate w hich is used in some cheaper soy milks and foods. I don't think w e should put all soy products in the same basket. Any research betw een the tw o?

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maurice :

04 Jun 2014 6:58:42pm

I w onder w hy natto is not mentioned? I also w onder w hy no distinction betw een fermented soy products and others, is not made.

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Erika :

04 Jun 2014 5:44:27pm

There is another issue associated w ith soy that isn't covered here: calcium absorbtion and w hether or not soy inhibits calcium absorbtion.

My view of the consumption of soy products is to avoid any soy products that involve very high temperature processing or processes that cannot occur in a normal kitchen. So soy sauce and tofu and the like are O.K. (in moderation), "textured soy protein" is not O.K., and soy milk should be avoided unless you are lactose intolerant and you can't manage tea and coffee w ithout putting a w hite liquid in it.

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Andi :

10 Jun 2014 6:21:37am

Erica, do you know tofu is made from soymilk? You can't say a product of something else is OK, but the original ingredient is not. Soymilk is healthy and cooked to the point w here it eliminates antinutrients but not too hot to remove all the goodness.

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