As a vegan physique athlete I get asked a lot about the soy products in my diet. It’s high in protein, moderate amount of fat and low in carbs. So a lot of vegan athletes will utilize these macronutrients to fit their eating regime. Personally, I eat about a block of tofu every day.  But isn’t that too much? What about the oestrogen? Won’t you grow man-boobs? What about cancer and GMO?

So I decided to write this short article to address these questions.

Estrogen in soy.
Put simply: the phytoestrogens (plant estrogens) found in soy are not the same as human estrogen. These compounds do not exhibit the same effects as human estrogen. It is not supported in any of the medical literature that men consuming soy products develop breasts or lowered testosterone levels. It’s purely myth coming from people confusing phytoestrogen and human estrogen. In fact vegan men may even have higher levels of testosterone than vegetarian and meat-eating men (1).

Cancer From Soy
This is another myth coming from the confusion between phytoestrogens and estrogen. Many people know that increased amounts of estrogen can lead to an increased risk of breast/prostate/ovarian cancer. So it’s understandable when people hear soy has “estrogen” in it they associate it with cancer.  But studies show that soy phytoestrogens do not exhibit the same tumour stimulating effects as estrogen. In fact, they are shown to have protective effects against tumour growth in the medical literature. (2,3,4).

GMO and Soy
Whilst it’s true that most of the world’s soybean crops are genetically modified (over 80%), most of this ends up as food for livestock animals (over 80% again!). Soy is high in protein and therefore used in many food preparations for farmed animals for meat or dairy production. So in a sense, meat-eaters are the highest consumers of GMO soy. Of course, you can find tofu & tempeh made from GMO soybeans, but most soy based products on the market are in fact organic/non-GMO and are labelled as such.

Too much Soy?
There is however something to be a little cautious of with soy though! Whilst some soy appears to be beneficial in suppressing certain cancers… there is a limit to this. When people start to eat soy in absolute excess (more than 18 servings a day), it seems that these benefits can be negated. This is due to the protein in soy being in similar amino-acid ratios as human or animal muscle tissue. The body can utilise these amino-acids very rapidly and therefore causes an increase in a certain growth factor (IGF-1) (5). This could lead to tumour growth which sounds scary, but this is the same thing which happens when people eat meat/animal protein too. But what doesn’t happen with animal-protein consumption is the increase of “IGF-1 Binding Protein” which does occur with soy consumption . This Binding-Protein basically reduces the levels of the IGF-1 in the blood (that’s a good thing). We’ll be talking more about the interactions of this growth factor in another article but in short for now: Eating between 3-5 servings of soy a day shouldn’t exhibit harmful effects on your body and medical literature even suggests that getting up to 3 servings daily is beneficial.

So overall, yes! Eat your soy products! But exercise moderation, you don’t want to make soy your only source of protein.

Note: A serving is 1 cup/250ml soy milk. Or about half a cup tofu/tempeh for example. 

Max is a certified personal trainer. Learn about him here!

Sources:
1. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2374537/pdf/83-6691152a.pdf

2. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology.
http://www.ncbi.nlm.nih.gov/pubmed/19221874

3. Soy Food Intake and Breast Cancer Survival
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2874068/pdf/nihms169338.pdf

4. Soy food consumption and breast cancer prognosis
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2874068/pdf/nihms169338.pdf

5. Insulin-like growth factor-1 and binding protein-3 in a 2-year soya intervention among premenopausal women.
http://www.ncbi.nlm.nih.gov/pubmed/16176606

6. Dietary soy and fats in relation to serum insulin-like growth factor-1 and insulin-like growth factor-binding protein-3 levels in premenopausal Japanese women.
http://www.ncbi.nlm.nih.gov/pubmed/12881012