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
