What’s the Deal with Soy?


What’s the deal with soy?

As a Registered Dietitian Nutritionist, especially one that specializes in plant-based diets, I constantly get asked about soy. I’m used to it, especially when the undergrad students I teach ask me about it. However, I was recently shocked when a few long-time vegan clients of mine told me that they were weary of soy. So, even though this topic has been written about by so many dietitians and other health-care professionals before me, I felt the need to contribute and get the word out. I couldn’t think of a better topic to write about for my first ever blog post here at Priceless Nutrition & Wellness!

The short answer to “what’s the deal with soy?” is - it’s healthy, perfectly safe, and great for both kids and adults! But, let’s delve a little deeper into why I say that and where the myths surrounding soy even come from.

I hear all types of myths when people ask me about soy or rather, tell me how terrible it is for you. “It makes men grow boobs.” “It causes breast cancer.” “It has estrogen and that’s why it’s bad for you.”  etc. Have you ever heard any of these as well?  

What is Soy Exactly? (A History Lesson of Sorts)

Soy is a legume that is indigenous to Eastern Asia where it is has been a significant part of the diet and a major source of protein for centuries. It wasn’t until the 20th century that soy was introduced to the Western World as markets for alternatives to oil and animal- feed proteins increased. The soy industry in North America has grown since the late 1950’s due to many reasons such as an increase in Asian immigrants, greater acceptance by the general public, and an increased recognition of health benefits. 

As a plant-based protein, soy really can’t be beat! The pattern of amino acids found in soy protein resembles those found in high-quality animal protein sources and soy protein products compare in digestibility to these animal proteins as well.

Soybeans contain isoflavones, which are referred to as phytoestrogens because of their weak estrogen activity. Due to this, it’s considered to be the most controversial plant food.  

Soy products include soy milk, tofu, tempeh, edamame, miso, and meat alternatives. One serving is equivalent to 1 cup (8 oz) of soy milk or ½ cup of tofu. 

Does Soy Really Cause Men to Grow Breasts?

I found one small study that is likely the culprit of where this myth came from, not to mention the countless social media accounts I’ve seen (even from medical doctors) who advise against soy for this reason. This one study provided men with the equivalent of 18-36 servings of soy protein per day in supplement form (not food) and 2 of the 20 participants developed minor feminizing of the chest area. But, really, who eats 18 servings of soy per day? I wouldn’t recommend it! As far as the people who describe this effect from soy on social media, remember where this information is coming from. Even a medical doctor should not be providing information that’s based on anecdotal evidence. Unless there’s a well-designed study comparing two groups of people - such as one consuming soy and one that abstains completely - we can’t say that there is scientific evidence supporting the notion that soy causes man boobs. 

Does Soy Really Cause Breast Cancer?

Soy contains phytoestrogens which are chemically similar to the estrogen we as humans have. Since it is similar, but not exactly the same, we don’t use it the same way when we ingest it. Phytoestrogens actually have been shown to reduce breast cancer risk, not increase or cause it. There are many studies that have concluded the health benefits of soy with regard to reducing breast cancer risk. So, overall the opposite is true when it comes to this myth. 

Does Soy Cause Infertility?

This is another unfounded myth where the opposite is likely true – soy may actually reduce infertility. When digging through the research, I found one study of 213 infertile couples that had higher rates of conceiving when undergoing in vitro treatment when both partners took phytoestrogen supplementation. Although that is based on supplementation, and I’d rather have evidence based on consuming whole food products, this review found that soy intake has not been indicated in reducing female fertility. Additionally, there is good evidence that soy intake may be beneficial to male fertility and at least has no effect on sperm quality as well! 

Is It Safe for Children to Consume Soy?

Just like for adults, soy is perfectly safe for children to consume and may be protective for their health as adults. Though there are not many studies on soy consumption and children, the research has not indicated that soy causes premature puberty, as some myths have indicated, and some studies have shown that adults who consumed soy as children have a lower chance of developing breast cancer. 

For children who are eating a plant-based diet, there are many benefits of including soy in addition to the health benefits I just mentioned. Not only is soy a great source of protein but it’s also high in calcium, iron, folate, zinc, and other B vitamins. All of these nutrients are particularly important for growing children and might be a little harder to obtain in a plant-based diet otherwise. 


How Much Soy Is Safe?

Since we know that soy can actually be beneficial to our health, I recommend individuals, especially those that are following a plant-based diet, to include it to their daily diet. The average daily intake of soy in countries such as Japan or China is 1.5 servings per day. Based on that, for both children and adults, I advise everyone to include up to 3 servings per day. 

Caveats On Soy

Although the benefits of soy are great, there are some things to be aware of when including it in the diet. One is that individuals with any thyroid issues should limit soy intake as it can interact with thyroid hormones. Another is that when choosing a product, organic soy is the best option because inorganic may be processed with hexane, a chemical that may be dangerous for consumption. Finally, although the research that we do currently have on soy is promising, we can certainly use more, particularly on children and fertility. I hope that in the years to come, we will have more especially as plant-based diets grow in popularity! 

Top 5 Take-Aways on Soy 

  1. Don’t believe the myths! Soy does not cause breast cancer, man-boobs, infertility, or early on-set puberty.

  2. Soy is protective to our health and might reduce our risk of breast cancer as well as increase fertility.

  3. Soy is safe and beneficial for children to consume and should be included daily for any child who is following a plant-based diet. 

  4. This legume is a powerhouse of nutrients – it’s a great source of plant-based protein, iron, calcium, zinc, folate, and other B-vitamins.

  5. Choose organic sources of soy when possible to avoid hexane intake.

My family and I have a few servings of organic soy on a daily basis mostly through soy milk, tofu, edamame, and tempeh. If you’re looking for some new soy-based recipes, check out my FREE plant-based meal plan. You’ll find recipes that include soy for any meal!

Do you now feel more confident including soy into your diet? Please leave a comment below if so!