Soy: Is it really safe?

Soy has a tumultuous history. One moment it’s being hailed as a super food, the next it’s potentially toxic. These mixed messages have resulted in widespread uncertainty around the consumption of tofu, tempeh, soy milk, edamame and miso due to reported links between consumption of soy and cancer risk.

But soy is an amazing source of protein for those following a vegan or vegetarian diet. And as you may have noticed, many of the vegetarian and vegan recipes on Centr contain soy products.

Unlike some plant proteins, soy protein is considered a complete protein, containing all nine essential amino acids.

“From a nutrition composition perspective, soy is a winner all round,” Advanced Sports Dietitian Lisa Middleton tells us. “Soy products have a high-quality balance of amino acids to assist in meeting protein requirements, particularly for active vegans. Soy products are also a useful source of calcium, and their versatility provides wonderful taste and texture options for a plant-based lifestyle.”

So what’s the problem?

Soy contains isoflavones, a type of plant estrogen (phytoestrogen) that is similar in function to human estrogen. This is where it gets tricky. Some claim these phytoestrogens have a positive effect on the body (soy is exalted as a miracle food by some, with claims of taming hot flashes, warding off osteoporosis, and protecting against hormonal cancers like breast and prostate) while others believe there is a link between consumption of these isoflavones and breast cancer, thyroid problems, and dementia.

“Studies have looked at the impact of soy on various health conditions, often with mixed or neutral results in conditions such as high cholesterol, breast and prostate cancer, cognitive function, thyroid function and reduction of menopausal symptoms,” explains Lisa.

“The effect of phytoestrogens is potentially weak, and interestingly can have a possible pro- or anti-estrogenic effect. “However it gets complicated, and the specific impact of phytoestrogens can be related to a range of factors such as ethnicity, age, individual hormone levels and the type of soy product.”

Harvard recently published an excellent break down on soy, and concluded that “soy is a nutrient-dense source of protein that can safely be consumed several times a week, and is likely to provide health benefits – especially when eaten as an alternative to red and processed meat”.

How much, and which type?

Different soy products contain different amounts of isoflavones, with miso, natto and soybeans likely to contain higher amounts per serving compared to soy milk, tofu and soy cheese.

But Lisa is quick to point out that higher isoflavone products are not necessarily “bad” – she just recommends you don’t consume high isoflavone products all the time.

She says your weekly vegan or vegetarian meal plan contain up to four servings of soy products, for nutrition and variety “and more tofu/edamame, tempeh and miso … and soybeans less regularly”.

The bottom line

Ultimately, more research is required to get a definitive answer on soy.

“As we eat a mix of whole foods, not single nutrients, we don’t really have a full understanding of the interaction between different foods and their specific influence on health,” explains Lisa.

“Research on the impact of soy on health conditions is still mixed, even though individuals within certain high soy-intake countries eat plenty of soy products and enjoy good health. It’s also important to remember that the results from studies done on animals or in the lab are not always applicable in humans – look beyond the headline to see exactly how research was done before jumping to conclusions.”