Niki Bezzant: Is soy good or bad for you?

Soy has been both praised and vilified in the past. Photo / Getty Images

From soy milk to tofu to miso, not all soy products are created equal, writes Niki Bezzant.

How much soy do you eat? If you're not vegetarian or vegan, you might say "very little", although you might be surprised at how much you do eat without realising it. Soy protein and other soy derivatives are fairly common ingredients in processed foods, including bread, cereal and snack foods.

So is soy healthy or unhealthy? You have likely seen conflicting advice about this if you've ever looked at the internet. Soy has been both praised and vilified in the past; it comes up on "foods to avoid" lists in diets and cleanses, as well as in "healthy foods" lists in more mainstream circles.

A recent study has come out on the positive side. The large Japanese study – looking at over 42,000 men and 50,000 women aged 45-74 – found health benefits for people who eat fermented soy products in particular. These are foods like miso – which most people will be familiar with – and natto, which may be unfamiliar. People who ate these foods had a significantly lower risk of death from any cause than people who didn't. The benefits didn't extend, however, to other soy foods like tofu and soy milk, with which there was no benefit found in this study.

Miso is a delicious, savoury paste made from fermented soybeans. You'll have had it in soup form, for sure, but it's also a great ingredient to use in marinades, dressings, sauces and other dishes where it adds super savoury depth. It's one of my favourite ingredients.

Natto, on the other hand, is definitely an acquired taste. It's a fermented soybean product – soybeans are fermented with a particular bacteria, Bacillus subtilis. The end result is a product with a slimy, stringy texture, and a pungent, blue-cheese like flavour and smell. It's the texture that non-Japanese people usually find a challenge, rather than the flavour. But if you ever get the chance to try it, I'd say go for it. Served with rice and condiments, it's an interesting tasty food with some known benefits.

The soybean is an intriguing food. Whole soybeans are high in fibre and protein, as well as containing healthy fat, folate and a range of vitamins and minerals. Soybeans – known as edamame – are available frozen in the pod and shelled, and a really useful ingredient to have on hand. Add them to stir-fries, curries, salads and vegetable side dishes, especially if you're cooking a meat-free meal.

When soybeans are fermented, as in miso, natto and tempeh, the fermented end products also contain probiotics, which we all know by now can have benefits for gut health and overall wellbeing. In the recent study, the authors point out that fermented soy products are richer in fibre, potassium and bioactive components than their non-fermented counterparts, which may help to explain the benefits they found.

The other things in soy – and the reason why it's been a controversial food at times – are the isoflavones, a class of phytoestrogens, which act like a weak estrogen in the body. This is why soy has been touted as both beneficial and harmful for fertility and menopause.

The current evidence seems to fall on the side of positive benefits in both these areas. Eating soy foods has been found to be associated with fewer menopause symptoms such as hot flushes, as well as with better fertility outcomes for women trying to conceive.

There's been speculation in the past about increased breast cancer risk being associated with soy intake. But a 2014 review found a benefit to soy – ie it seemed to lower the risk of breast cancer – in Asian women, and no association between soy and breast cancer in Western women.

That last point is interesting. In Asian cultures, where soy foods have been part of the diet for thousands of years, people tend to eat soy in less processed form. They're eating whole beans, fermented beans, tofu or soy milk (the last two are made by pressing the whole beans and using the curd and/or liquid from soaking. In Western cultures we're eating most of our soy as an ingredient in processed foods; something that's been removed from the bean and further processed .

As with many categories of foods – like other vegetables and fruit – the benefits from soy seem to be wrapped up in the whole (or nearly whole) food, rather than in isolated components within the food. So just as we're better off eating an orange than taking a vitamin capsule, we're likely to get more benefit from soy foods – and less of any potential risk – if we eat them in as whole a form as we can.

* Niki Bezzant is a food and nutrition writer and speaker. Follow her on Facebook or Instagram @nikibezzant