Oh boy. So much has been written about soy online that it can be difficult to sift through the information and misinformation to get to the plain truth. So we decided to collect it, collate it, and compile it here for your quick and easy consumption.

Before you get started, please keep in mind this article should be considered general advice only, and should absolutely not replace the advice or instructions of your doctor. All bodies are different, and your doctor knows your body, and your medical history, much better than we do! All citations have been collected below the article if you feel like some soothing bedtime reading.


Are soy beans genetically modified?

Yes, usually. Buy organic, or certified organic.

About 80% of all soy bean crops planted globally are genetically modified[1], so it’s safe to assume a product contains GM-soy unless it explicitly states otherwise.

Genetically modified soy beans are most commonly altered to improve their resistance to weed killers and pesticides, which means GM-soy can be sprayed with larger quantities of more toxic spray without dying. Not surprising then that these chemical sprays may find their way onto your plate, with studies finding high residues of glyphosate and AMPA in genetically modified soy bean products. Studies have also shown that organic soy beans show the healthiest nutritional profile[2], containing more total protein, zinc, and sugars than conventional (non-GM, non-organic) and GM-soy beans.

While many countries, like the US[3] and Australia[4], do not allow the use of GMOs in certified organic products, this rule does not apply everywhere. Depending on where you live you may need to look for “non-GMO” or equivalent on product labels.


Are soy crops bad for the planet?

Yes, primarily because of their use as animal feed.

Soy is the second largest agricultural driver of deforestation worldwide, with only a small percentage worldwide sustainably grown[5]. The cultivation of soy is responsible for a number of ugly things, including habitat loss, biodiversity loss, and severe erosion.

The solution, ironically enough, is to eat MORE soy. Globally, 75% of all soy beans grown are used as animal feed[6], directly contributing to the largest agricultural driver of deforestation: the beef industry. Eat less meat (or none at all), and buy sustainably grown soy where possible.


Is there a link between soy products and breast cancer?

Probably not, but it’s complicated.

There is no clear scientific evidence that eating a moderate amount (one or two serves per day) of soy increases your risk of breast cancer[7], though there is evidence to suggest that a long-term diet rich in soy foods may actually reduce the risk. This reduction is unfortunately most pronounced for those who start eating it at a young age.

That said, science has found a possible link between soy (isoflavone) supplements – commonly prescribed to alleviate menopausal symptoms – and an increased risk of breast cancer[8], especially in women who have a family or personal history of breast cancer, or thyroid problems.

In summary: Soy foods are fine (one or two serves per day), but soy/isoflavone supplements are – generally speaking – not a good idea.


Is soy safe for boys to eat? For men?


One or two serves of soy per day is perfectly healthy and will not affect your boy’s testosterone production[9]. It won’t affect a man’s testosterone either[10].


Does soy affect gut health?

Maybe. Listen to your body.

There is some evidence to suggest a diet high in soy can negatively alter the balance of the gut microbiome[11], though other evidence suggests these changes could be good for your health[12]! In a situation where there is no clear evidence either way, it is important to listen to your body. If you feel that soy is negatively affecting your digestion, limit yourself to one or two serves of organic soybeans per day and consider supplementing with a probiotic.


Does soy cause thyroid problems?

No, but be careful if you already have thyroid problems.

Soy won’t cause thyroid problems if you’re getting enough iodine in your diet (iodized salt, sushi seaweed, etc)[13]. If you are on medication for hypothyroidism you should talk to your doctor about eating soy – consensus view is to wait at least four hours after taking your medication before consuming soy[14]. This is because the isoflavones in soy can interfere with the proper absorption of thyroid medication, so it’s best to give your body some time to absorb the medication, after which soy won’t be able to interfere.


Will soy cause kidney stones?

No, but may exacerbate if you’re prone to kidney stones.

If you have a history of kidney stones you should be careful to not overdo your soy consumption. Soy contains oxalate (a component ingredient of kidney stones) and phytates (an inhibitor of kidney stone formation). In small amounts these may be beneficial to kidney stone patients or those at high risk of kidney stones[15], while in larger amounts they may actually worsen your susceptibility if you have a history of kidney stones[16]. As mentioned before, stick to one or two serves of whole soy per day and you should be fine, but consider discussing with your doctor if you are concerned.


Is soy nutritious?

Yes, but it’s not a super food.

Soy is packed with nutrients: protein, iron, calcium, magnesium, potassium, dietary fibre, and more. It is one of the few “complete” plant-based protein sources, meaning it contains all the essential amino acids necessary for human nutrition[17]. It can help lower your “bad” cholesterol (LDL).

A great many scientific studies have been published detailing tentative links between soy consumption and health benefits or health risks. We suggest paying attention to these studies once the science has settled a bit – until then we’ll stick with what we know for sure.


In Conclusion

The evidence is clear: soy is nutritious and perfectly safe to eat if you are a normally healthy human being, no matter your age or gender. Don’t go mad on quantity: stick to one or two servings per day. Buy “whole” soy – try to avoid if the ingredients list mentions “soy protein isolate”. Buy organic if possible, and support sustainably farmed brands if you can.

It can be intimidating to adopt a plant-based diet, because there is so much to learn and so many traps lying in wait. If you feel like you could use some (non-judgemental) help and support why not join our Facebook group? Our supportive community would love to help you make a success of it!



  1. ISAAA: Pocket K No. 16: Biotech Crop Highlights in 2018
  2. PubMed: Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans.
  3. USDA Organic 101: Can GMOs Be Used in Organic Products?
  4. Choice: Are you eating genetically modified food?
  5. WWF: The story of soy.
  6. WWF: Soy: The Biggest Food Crop We Never Talk About.
  7. Mayo Clinic: Will eating soy increase my risk of breast cancer?
  8. ScienceDirect: Isoflavones
  9. Harvard Health Letter: By the way, doctor: Children and soy milk
  10. ISSM: Does consuming soy affect a man’s testosterone levels?
  11. FASEB: The Impact of Dietary Soy on Gut Microbiome
  12. PubMed: Soy and Gut Microbiota: Interaction and Implication for Human Health.
  13. PubMed: Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature.
  14. Mayo Clinic: Is it true that people who have hypothyroidism should avoid soy?
  15. PubMed: Oxalate and phytate of soy foods.
  16. Science Daily: Too Much Soy Could Lead To Kidney Stones
  17. PubMed: Soy: a complete source of protein.

Gabrielle is an evidence-based vegan coach who believes that health transformation begins when you switch to a plant-based diet. Her mission is to help midlife women eat in alignment with who they are and what they value so that they can lead a happier, healthier and more fulfilling life.

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Written by Gabrielle (hi!), these e-mails will help you on your plant-based journey with useful tips, tricks, facts and inspiration – and perhaps the occasional inappropriate joke thrown in for good measure.

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