Pros and cons of soy

Jane Murphy / 15 February 2017

Soy has been hailed as a superfood, but recent studies suggest soy may not be such a healthy choice after all. So what's the truth behind the headlines?



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What exactly is soy?

Soy – or soya – is a bean with many guises. It can be eaten fresh from the pod (known as an edamame bean); unfermented as soya milk and other dairy alternatives, tofu (bean curd) and meat replacements, such as mince and textured vegetable protein (TVP); and fermented as tempeh (bean cake) and miso (bean paste).

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What are soy's main health benefits?

'It's an excellent source of protein, so can be especially beneficial for vegetarians and vegans, who don't eat any animal protein,' says Rob Hobson, registered nutritionist at Healthspan and co-author of The Detox Kitchen Bible. 'It also contains calcium, which is needed for good bone health, so may be of particular benefit for post-menopausal women, who can lose up to 10 per cent of their bone density.'

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But calcium isn't the only bone-building hero found in soy: it's also the main dietary source of plant chemicals called isoflavones, which are similar in structure to the human hormone oestrogen. A diet rich in soy proteins and isoflavones can significantly improve bone health and reduce risk of osteoporosis after the menopause, according to a recent study at the University of Hull.

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Soy is also a good source of essential minerals including iron, magnesium and potassium, as well as vitamins B6, E, K and folate. It's naturally low in saturated fats and sodium, and has a low glycaemic index, which means soy carbohydrates are released slowly and steadily to help keep blood sugar levels steady.

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Great! Anything else in soy’s favour?

Some researchers have suggested that soy isoflavones can help reduce menopausal hot flushes. However, a recent British Pharmacological Society study review concluded that these positive effects were generally 'slight and slow' – so nothing to get too excited about.

There's also good evidence that soy may slightly reduce levels of heart-harming LDL cholesterol.

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OK, so what about all these soy scare stories?

'Much of the controversy surrounding soy is related to breast cancer risk and treatment,' Hobson explains. 'But the consensus from the available research is that consuming moderate amounts of soy – one to three servings daily – as part of a balanced diet is fine.'

Admittedly, though, the available evidence can be confusing. Recent research at Georgetown University Medical Center in the US suggests that long-term soy consumption may improve the effectiveness of a common breast cancer treatment, tamoxifen, and reduce recurrence. But eating soy for the first time while being treated with tamoxifen can lower its effectiveness and increase chances of the disease recurring. So do ask your doctor's advice before consuming soy if you're receiving breast cancer treatment.

'Soy isoflavones have also been linked to hypothyroidism as they may inhibit the function of a key enzyme in the thyroid,' says Hobson. 'But much more research is needed on this.'

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Anything else I should be worried about with soy?

Some of the other plant chemicals found in soy, such as phytates and oxalate, can sometimes inhibit the absorption of minerals, including calcium, iron and zinc. However, recent studies show these minerals are usually well absorbed from soya when eaten as part of a healthy, balanced diet. What's more, the phytate content can be significantly reduced during the fermentation process – so it's not always a concern.

How does soya milk compare to cow's milk?

'Always choose a soya milk that's been fortified with vitamins and minerals, such as bone-building vitamin D,' Hobson advises.'Other than that, soya milk contains around the same amount of calories, but less fat and protein than semi-skimmed milk. Cow's milk contains more vitamin B12, which is essential for brain health, than soya milk and around the same amount of calcium.'

Is the vegan diet healthy?

So it's OK to keep soy on my shopping list then?

'Yes,' says Hobson. 'But do opt for soy foods that aren't genetically modified or overly processed. Fermented varieties, such as miso and tempeh, appear to be the most beneficial, but all can still offer a healthy contribution to your diet.'

Visit our food section for delicious recipes including soy

Supergreen vegetable stir-fry with marinated tofu

Scallops with soy, ginger and spring onions

Quinoa salad with tenderstem broccoli, chilli dressing and soy beans

Cheesy lattice pie with quorn

Japanese griddled chicken with bean and radish salad


The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.