Is soy safe when trying to conceive? You’ll hear some people tell you that soy is a fertility superfood, whilst others say that you should avoid it at all costs… well, as a dietitian, I always look to the research, so in this blog, I’m going to show you what the evidence says… 

There’s a variety of foods that are made from soy beans… tofu, edamame, soymilk, soy protein powders, miso and tempeh, to name a few… not to mention that it’s a commonly used ingredient in processed foods. 

We know that other beans and legumes, such as chickpeas and lentils, are great for us when we are trying to conceive..

So why is there so much fuss about soy? 

Well, soybeans are one of the richest sources of a compound called phytoestrogens.  “Phyto’ means ‘plant’, and I’m sure that you already know that estrogen is a key hormone that impacts fertility. These compounds are called phytoestrogens because they are found in plants and have a very similar structure to human estrogen. So, the obvious concern becomes does this additional plant-based estrogen impact our hormone levels? And therefore, impact our reproductive cycles, and our ability to conceive?

In short, the answer is yes, phytoestrogens can impact our fertility hormone levels, but it appears to be mainly for good.  However, let’s take a closer look at who soy-containing foods are good for, and who may need to be careful….

Before I get into the nitty gritty, it’s important to note that the US Food and Drug Administration and other government bodies state that soy is safe when trying to conceive and during pregnancy, so we don’t need to stress out and avoid every tiny little bit of soy.  For most people, soy-containing foods will be a nourishing choice. 

Now, for that nitty gritty… 

Hormone levels such as Follicle Stimulating Hormone (FSH) and Estrodial (which is a type of estrogen hormone), are often used by doctors as an indicator of a woman’s fertility status.  This is because high FSH and estrodial during the follicular stage of the menstrual cycle, have been associated with low pregnancy rates. Studies suggest that phytoestrogen consumption may help lower FSH levels, which in turn may boost fertility in some women. Lowering your FSH levels may lengthen your menstrual cycle, so whether this is beneficial or not for you, will depend upon your current cycle. 

The impact of phytoestrogens on estrodial is much more conflicting and more research needs to be done on this to be able to give a clear recommendation. Based on the current evidence, phytoestrogens don’t seem to have a very big impact.  

It’s also interesting to note that high intakes of phytoestrogens may impact sperm concentration. So while phytoestrogens are generally good for most women’s fertility, they may not be as beneficial for men. But, there’s still a lot more research needed in this area. If your partner’s sperm count is good, I don’t believe that he needs to avoid soy, but if his sperm count is low, it may be worth cutting back until after you have finished having babies.

Back to women… Previously we discussed that soy may impact your thyroid hormones if your iodine intake is low. As long as you are meeting your iodine requirements, soy foods won’t impact your thyroid hormones, but if you’re unsure, it’s worth speaking to a fertility dietitian, and avoiding a large intake of soy foods until you get a bit more personalised information.

So, to summarise, here’s what I would recommend… 

• Firstly, avoid soy supplements unless specifically advised by your health care practitioner, as these do contain concentrated doses of phytoestrogens.
• Secondly, unless you have thyroid problems or irregular menstrual cycles, consuming a few serves of soy-containing foods in your eating plan each day is more likely to be beneficial for your fertility than harmful.  However, as always, it’s best to get individually-tailored advice from a qualified dietitian.
• If you do have thyroid problems or irregular menstrual cycles, it doesn’t mean that you need to avoid soy foods altogether, it just means that it’s a little more complex and it’s worth getting personalised advice.