This is a common thing that you have heard frequently from fitness influencers, gym buddies & few trainers too. That you should avoid having soya chunks or soy products in your diet bcoz it will make your chest as breast aka “ Man Boobs” or in medical terminology “Gynecomastia”.
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Oh is it true? Do you think so?
Let’s dive deep into this.
Soya chunks: It is also called as meal-maker or Soya-Badi in India. It is made of soybeans. Soybeans come under legumes just like other pulses. This is a completely plant-based product which is very common among vegans & vegetarians. Bcoz of its chewy nature & texture, it is also known as mock meat. In Industry, soybeans are processed to prepare soya chunks. Soybeans have fat, carbs & protein, but after processing in the industry, the final output soya chunks have a good number of protein & few amounts of carbs with a negligible content of fat.
Soya chunks have a very good amount of protein. [1]. In 100gms of Soya chunks, we get 53gms of protein, which is the highest amount of protein that we can get from any plant-based food item.
That’s why it is a very important source of protein for vegetarians. Generally, 100gms of chicken has 24gms of protein whereas 100gms of soya chunks has 53gms of protein.
We get more protein from soy but the quality of protein we get from soy is low in comparison to the animal protein just like egg & whey protein in terms of Protein efficiency ratio, Biological value, Net protein utilization. [2]. This says that it is the best protein source for vegans. [3]
On the web you will get a lot of articles, few famous fitness influencers & doctors also say that soy products will alter your sex hormones, especially your testosterone & estrogen levels.
But till now there is no scientific evidence or clinical studies which state that consuming soy products will increase your estrogen & will decrease your testosterone.
Then from where does, this thought comes into the mind of fitness intellectual?
Soy products have a compound called isoflavones in them which are also called phytoestrogen.
Phyto means plants
Estrogen means female hormones.
When this phytoestrogen interacts with our sex hormone especially testosterone & estrogen. It binds with respective receptors thereby decreasing testosterone & increasing estrogen in our body.
And as it increases our female hormone it causes man boobs & feminine characteristics in us. But the story is a little different if we dig deep into this.
Let’s understand what are these estrogen receptors. To pass on the message to our cell membrane our hormones need these receptors. It can be considered as a lock & key mechanism. Where hormones are the right key when plugged into the right receptors i.e the lock, then only the message will be transmitted to the cell membranes. As a result of this changes in our body happens.
But the phytoestrogen that we get from our diet has a very weak affinity towards the receptors in comparison to our naturally occurring estrogen & testosterone. Due to this weak phytoestrogen does not have any effect on our body.
Another reason for this misconception is a rat study [4]. Where it is evident that when the adult rats are given Daidzein (a form of isoflavone) 20mg/kg & 100mg/kg of body weight for 90 days then there is a significant drop in their plasma testosterone level.
But even if we consider this study then also it is not harmful to our body. Let’s do the calculation.
1gm of soy protein = 3mgs of Isoflavones
100gms of Soya chunks= 53gms of Soy protein
So, it has 53*3= 159mg of Isoflavones
So if your weight is 75Kg & you consume 100gms of soya chunks.
Then you will be having 159mg/75Kg= 2.12mg/kg
So your body gets only 2.12mg of isoflavones /kg of body weight.
Which is very low in comparison to 20mg/kg of BW that was given to rats during the study.
Now, let’s see how much soya chunks are needed to consume 20mg of isoflavones/kg of Bodyweight.
For a 75kg weight person
75*20mg/kg=1500mg of Isoflavones.
1500mg/3= 500gms of Soy protein
So as 53gms of soy protein are there in 100gms of Soya chunks. To get 500gms of Soy protein only from soya chunks we have to consume around 950gms of soya chunks. Which is a huge amount if consumed on daily basis. So as per the rodent study to get feminine characteristics or man boobs you have to consume 950gms of soya chunks for 90 days.
Moreover, even if you try to complete your protein requirement only from soya chunks on daily basis. Then also this much of soya chunks is not needed as 200-250gms of protein is enough for our body.
A 2010 study consisting of a meta-analysis & research shows that neither isoflavone supplements nor isoflavone-rich soy affects our total or free testosterone level.[5] Findings from animal studies suggesting that isoflavones increase the risk of erectile dysfunction do not apply to men, because of differences in isoflavone metabolism between rodents and humans. Thereby, indicating that isoflavones do not exert feminizing effects on men.
One more recent meta-analysis of 2020 [6] shows that total testosterone, free testosterone, estradiol, estrone & sex hormone-binding globulin SHBG does not have any effect regardless of dosage & duration of soy protein & isoflavone exposure.
A 2007 study was done on 20 men for 12 weeks, where they are given 50gms of protein from 4 different sources.
- Soy Concentrate
- Soy Isolate
- Soy Isolate & whey Blend
- Whey
Along with this they also did resistance training. And after 12 weeks it is seen that there is no significant change in any group regarding total & free testosterone, body fat percentage, BMI & SHBG (sex hormone-binding globulin). Thereby concluding that soy protein neither decreases serum testosterone nor inhibits lean body mass.[7]
All these studies depict that soy protein does not create any imbalance in our sex hormones or develop any feminine characteristics like man boobs. In India, soy chunks & soy product consumption is anyways less in comparison to other Asian countries like China, Japan & Korea. Where the soy product consumption is too high in form of Tofu, Soy milk, Miso, Tempeh, Natto, etc. Had the above misconception been true almost every person in those countries would have faced issues with infertility & gynecomastia. But there is nothing like that. So it is just a personal assumption of people who believes in this myth. As there is no scientific study available till date which supports this claim.[8][9][10]
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