Just soya know
Dietitian Laura Tilt digs deeper than the headlines to reveal the truth behind those soy scare stories
We dig into the debate on the humble soy bean – dietary victim or villain?
FFS. Tofu? How can tofu be bad for you? I get it. Just when you think you’ve knocked the dairy debate on its head, scary soy claims make you want to throw out the contents of your freshly stocked fridge. Sales of soy have soared in recent years, but it’s often suffered bad press, with studies linking female consumption of soy to breast cancer and even infertility. Yikes!
So, where do these fears stem from? Glad you asked. Most are linked to the naturally occurring phytoestrogens (hormone-like plant compounds) in soy, known as isoflavones. Phytoestrogens mimic the effects of oestrogen in the body, leading to concerns that soy may be harmful due to a link between high oestrogen levels and health risks, including breast cancer – oestrogen increases cell division and may therefore contribute to the growth of cancerous cells.
But the plot thickens. In a 2008 study published in the British Journal of Cancer, researchers found breast cancer risk was significantly reduced in women consuming high amounts of soy (providing more than 10mg isoflavones), compared with those eating smaller amounts. Quite the turnaround. The science behind it? In short, this can be explained by the presence of two oestrogen receptors in the human body – alpha and beta. When it comes to breast cancer, alpha poses the biggest risk. According to experts, these isoflavones preferentially bind to the beta receptor, which may actually have a protective effect.
Cancer risk aside, a quick google of ‘soy’ and ‘fertility’ is enough to make you ditch the soy lattes for good. It comes down to the link between genistein (the primary isoflavone in soy) and reduced fertility in studies done on sheep, mice and rats. The good news? These studies typically involved consuming genistein at levels five times higher than those you’re exposed to by eating food containing soy, so there’s an element of scaremongering here.
In fact, more recent research suggests soy might actually be good for fertility. In a 2015 American Society for Reproductive Medicine study of women undergoing fertility treatment, isoflavone intake was positively linked with live birth rates. And, according to a 2016 study in Nutrients, soy isoflavones may even protect against the negative effects of BPA (the chemical found in plastic and cans) on fertility.
The upshot? There just isn’t enough convincing evidence in human trials to suggest you need to ditch soy. (High fives all round!) When it comes to fertility, there are arguably more impactful things to consider; carrying too much or too little body fat, smoking, booze and high stress levels can all negatively affect your baby-making chances. Also, eating soy protein as part of a healthy diet has been linked with a lower risk of heart disease, which is yet another reason not to ditch it. Edamame me up, baby!