Is it safe to eat or drink soya when you're trying to conceive?

Currently, there’s no scientific evidence that definitively proves one line of thinking right over the other. As a result, dieticians say there's no need to avoid soya when you're trying to conceive.

If you consume loads of soya products, you may decide you want to switch to another type of milk or meat alternative. That's totally your call, though.

How could soya products affect female fertility?

Soya (also known as ‘soy’ in the US) is found in lots of our food. More than you’d think, too: it’s in roughly 60% of processed food, according to reports.

Lots of us also eat tofu, edamame beans or soya yoghurt, drink soya milk, or enjoy a bit of soy sauce with Chinese cuisine – these are all products that are made from soybeans.

So, how could all this soya in our diets affect fertility in a negative way? What’s in it?

Nutritionist Caroline Bunker explains that soya contains a type of the hormone oestrogen, which can affect our periods and fertility.

“It's all because soya contains a form of oestrogen - called phytoestrogen. Experts already know that oestrogen can suppress ovulation.

"But it's not clear whether phytoestrogen has exactly the same effect as oestrogen until more research is done.” Hmmmm.

What do scientific studies show?

Indeed, things remain similarly murky when you look into what the science-types have found in their research.

A few studies have been done which suggest that there could be a link between female fertility issues and soya - however, these are mostly animal studies.

One such study, published by journal Reproductive Toxicology, showed pretty plainly that female mice saw a decrease in fertility after being given soya.

But then, we’ve also seen studies which claim the opposite – and suggest maybe MORE soya could be beneficial. Huh?

A Harvard study published by the Journal of Endocrinology & Metabolism which explored whether soya could help counteract the harmful effects of the BPA [bisphenol A] chemical found in some plastics, for women having IVF.

They looked at data from 239 women, including their pregnancy rates, the BPA levels in their wee, and their soya consumption.

Lead researcher and Harvard associate professor Dr Jorge Chavarro told US site Fit Pregnancy of the results:

"We found that among women who were undergoing infertility treatment with assisted reproductive technologies, urinary bisphenol A levels were related to a lower chance of having a live birth—nearly 50 percent lower chances—among women who did not consume soy foods.

"But [BPA] had no impact on live births among women who did consume soy."

The idea follows that effects of BPA, which can affect fertility (a whole other story), can be cancelled out by soya, and that this should apply to actually trying to conceive, too.

However, Dr C also noted: “Even though we did our best to rule out and account for other factors that could explain this interaction, such as other characteristics of women's diet or of their medical and reproductive history, there is still a chance that some other unmeasured factor could be responsible for the interaction we identified."

What the experts say

Is your head spinning? Our heads are spinning. There have been lots of smaller studies on the subject of female fertility and soya, and they all say different things. Nothing's been proven 100%, however.

So MadeForMums decided to speak to Specialist Dietitian and British Dietetic Association (BDA) spokesperson Nicole Rothband, for a definitive answer on the subject.

"There is insufficient conclusive evidence that dietary soya disrupts hormone balance or significantly affects fertility. Dieticians in the UK would not routinely recommend soya avoidance to people trying to conceive.

"There is research that has generated headlines about soya affecting fertility but many have been animal studies and the results cannot be generalised to humans.

"The methodology of human studies frequently cannot establish a causal link be between soya consumption and fertility.

"The quality and methodologies of human and animal studies are variable, so more double-blind randomised controlled studies in humans are required to create the required body of evidence."

Basically, Nicole's saying you DON'T need to avoid soya, and that lots more research would have to be done to change that recommendation.

MFM's go-to GP Dr Philippa Kaye agrees, adding: "Currently there is no guidance that people trying to conceive should avoid eating soy and soya products. Soy contains isoflavones, which are phytoestrogens - these may act in a similar way to oestrogen in the body.

"And if you are pregnant again it is safe to eat soy, as part of a healthy balanced diet. So enjoy your tofu and other soy based products."

Note that the official NHS website doesn’t mention that TTC women or couples need to avoid soya, in their piece on soya and pregnancy (last reviewed in April 2018):

"The only people who are advised to restrict soya intake on account of phytoestrogens are people with hypothyroidism, women who have been diagnosed with breast cancer and babies who have soya-based infant formula.”

Can soya affect male fertility?

Now, there’s also long been the suggestion that soya can muck up male fertility. So, does your partner need to avoid soya to keep his sperm plentiful, mobile and healthy?

Some studies would say yes. For example, the Human Reproduction journal published a study that showed men who didn’t eat soya (and, importantly, were already visiting a fertility clinic) had higher sperm concentrations than those who ate just half a serving a day.

The NHS website suggests the opposite, citing another headline-grabbing study that claimed soya affects sperm quality. In a 2008 article explaining the study, it states:

“This small cross-sectional study suggests a link between soy and sperm quality. The idea that soy affects male fertility is not new, and there is a growing body of research on it.

"There are contradictory results from studies in this area (both human and animal studies), including the argument that the Asian diet (high in phytoestrogens from soy foods) has no apparent effect on fertility.

“Others support the view that soy has a positive or null effect on sperm quality. As the researchers state, this lack of consistency – particularly between animal and human studies – 'highlights the importance of conducting further studies in humans'.

"Until then, there is no harm in men who have low sperm counts who are trying to conceive and who are worried about their sperm counts falling further, limiting their intake of foods containing soya.”

Dr Philippa echoes this sentiment quite clearly: "There was a study a few years ago which suggested that men eating soya products had a decreased sperm count.

"However the study was small and flawed in design, for example the majority of participants were overweight or obese which may in turn affect phytoestrogens and sperm count and quality. Other studies have shown that eating soya has no effect on sperm count at all."

Again, we think this is another case of: too many conflicting opinions, and not enough cold hard proof. Therefore, men are fine to continue eating and drinking soya products, as well.

Image: Getty Images

Read more:

• Do decongestants like Sudafed impact fertility?
• Can you take antihistamines when trying to conceive?
• KY Jelly and lube - can that affect your fertility?