Note: This topic is far more complex than most people think. I had to read through tons of scientific studies to be able to produce this piece and in some cases, I was quite out of my depth and had to rely on AI tools to understand what was being said.
For this reason I asked my friend Dr. William (Bill) Lagakos (PhD Nutritional biochemistry and physiology) to review the article in full and he has confirmed that the article is comprehensive and does not contain errors to his knowledge.
Given the length and complexity of the article, this took him many hours to do so GO AND FOLLOW HIM ON X BY CLICKING HERE as a thank you.
In the previous part of this series, I talked about milk and dairy products and if they are safe for human consumption.
In this section I’m going to talk about soy and the various issues related to it. This is going to be a long read but once you finish it, you will understand the topic in detail.
Why Even Talk About Soy
The reason it’s necessary to talk about soy as opposed to just dismissing it as an “estrogenic” product is that it’s really cheap compared to whey protein.
We’ve all been broke before. A little over a decade ago, I used to make $150 a month. Now I make hundreds of times more than that thanks to affiliate marketing, my tax/law consulting biz, a few SaaS companies, and even this hobby blog.
There’s nothing wrong with being broke as long as you’re taking active steps to fix it. For the vast majority of people, the answer is to build some sort of online business.
If you’re a regular reader, you’re already making tens of thousands of dollars each month from the internet and nodding in agreement.
Of course there are always losers who lack the brain and balls to take action. These guys will never make it regardless of how much information they read on this website or anywhere else.
At the time of writing, soy protein isolate costs 65% less than whey protein concentrate and 80% less than whey protein isolate. The ratio may change over time but I expect soy protein to still be considerably cheaper than whey protein for the decades to come.
The prices I can currently see on Amazon are here for reference:
Whey protein concentrate: ₹2299 (~$26 per kg) [MuscleBlaze]
Whey protein isolate: ₹3999 (~$46 per kg) [MuscleBlaze]
Soy protein isolate: ₹850 (~$10) per kg [Couldn’t find a brand I recognized but most products are around this price]
In other words, you can buy 5 kg of soy protein isolate for the price of 1 kg of whey protein isolate.
For many lower income people, this can mean the difference between getting a high protein diet and eating a low protein diet.
Someone making $300-500 a month is never going to be able to afford to eat lots of whey protein. Even at 2 scoops a day, he needs 1.5 kg a month which will cost a significant percentage of his income if he chooses to buy whey protein.
On the other hand, 1.5 kg of soy protein isolate will be easily affordable (especially when you account for the fact that it replaces a non-protein meal and offsets some of the costs).
If you look at soya chunks, also called textured vegetable protein (TVP) or textured soy protein (TSP), the prices are even cheaper.
In other words, for many people especially in poorer countries, soy products are a source of protein that they can actually afford.
It can be the difference between getting enough protein and eating a low protein diet. It merits a more serious look than just being dismissed as a meme food that will turn you into a girl.
Soy is actually a very good protein source
Soy has been massively demonized over the past few decades. More recently, it has turned into a meme. If you are a left wing dork, you are going to be called a soyboy.
I’ve personally been a part of this too. I’ve mocked all sorts of dorks by calling them soyboys. It’s a meme. And I’ve always been against any soy consumption.
But as I looked into it further, I realized that I was wrong. Soy is not as bad as this side of the internet makes it out to be and the claims against it are overstated.
Recall from the piece on protein quality that soy is one of the highest quality plant based protein sources available to man.
The amino acid profile is similar to meat and the PDCAAS and DIAAS scores are comparable to animal protein sources like chicken.
When it comes to plant protein quantity and quality, nothing beats soy.
Cooked soy products are also highly digestible and their anti-nutritional factors become much less of a problem.
Soy protein isolates are even better than whole soy products because they have almost all of their anti-nutritional factors and plant cell walls removed making it comparable to whey protein in digestion efficiency.
Soy protein isolate is comparable to meat in quality but is slightly worse than whey protein because of its lower leucine content (everything is worse than whey protein in leucine percentage – see chart below).
This is already covered in the piece on BCAAs and Leucine but I’ve reprinted it below for convenience.
Leucine and BCAA content in a variety of foods
| Food | Leucine | BCAAs (Leucine + Isoleucine + Valine) |
| Whey protein isolate | 11% | 22% |
| Milk protein | 10% | 21% |
| Meat protein | 8% | 18% |
| Soy protein isolate | 8% | 18% |
| Wheat protein | 7% | 15% |
Note that some soy protein isolates are fortified with BCAAs and contain even higher values of leucine than whey protein isolate. But they are usually more expensive.
Such soy protein powders are pretty much as good as whey protein as far as protein quality is concerned. Yes it might be more processed and have other issues, but as far as protein is concerned, it’s the same thing.
There is no difference between the amino acids in your bloodstream even if they come from different food sources.
A molecule of leucine (or any other amino acid) in the bloodstream is a molecule of leucine in the bloodstream whether you get it from eating chicken, fish, milk, legume, soy, grain, or whatever else.
They are chemically and structurally identical. You cannot tell them apart short of marking them with a radioisotope (which is often done in research).
Again, all of this has already been covered in detail in this series already so I won’t be going over all of that again. If you want to learn more, read the previous parts.
The short version is that soy protein is very good quality protein. Processed soy foods and soy protein isolates are highly digestible as well.
And this is true regardless of your feelings about soy. I know soy has become a meme but that doesn’t change facts.
The Phytoestrogen Controversy Around Soy
I already covered the role and types of estrogen in the previous part of this series so I won’t be repeating it in this one. Read the previous part for a whole bunch of background information necessary to understand this one.
The main controversy in soy comes from the isoflavones present in it.
Isoflavones are compounds that have a structure that allows them to bind with the estrogen receptors in the human body and weakly mimic the effects of estrogen. This is why they are also called phytoestrogens.
Isoflavones do not activate the estrogen receptors as much as actual estrogen does, hence they “weakly” mimic the effects of estrogen.
The weaker than estrogen argument
The strongest isoflavones in soy are 10-10,000 times weaker than Estradiol (E2), the main estrogen in humans.
You might be inclined to think that isoflavones don’t matter because they’re so weak compared to actual estrogen, but if the story was that simple it wouldn’t really be a controversial subject and this article would not have been necessary.
We know that the human body produces estrogen every day in micrograms (μg): 40-50 μg per day in adult males.
On the other hand, isoflavones in soy are present in tens and hundreds of milligrams (mg).
For those of you who have forgotten basic math, 1 mg = 1000 μg.
The sheer quantity of isoflavones in soy is so high that despite the “weak” activation of the estrogen receptors, the effect can start to add up.
And 30-50% of people have digestive enzymes that can turn some of the weak isoflavones into something much stronger (called S-Equol).
The conjugation argument
But then we know that after a soy meal, a very large portion of isoflavone in the bloodstream are glucuronide/sulfate conjugates that are essentially inactive at estrogen receptors (ERs).
So by that logic soy consumption should be entirely safe.
But then it turns out that many tissues in the body can de-conjugate them.
And then things are not so clear again.
The Japanese eat a lot of soy argument
Then some people make the argument that people in some Asian societies (like Japan) eat soy every day. The claim is made that they eat “lots of soy” and make it sound like they eat nothing but soy.
But actual studies and estimates show that the soy consumption in east Asia is not especially high. Quoted from the linked study:
The results indicate that older Japanese adults consume approximately 6-11 g of soy protein and 25-50 mg of isoflavones (expressed as aglycone equivalents) per day… Evidence suggests that < or =10% of the Asian population consumes as much as 25 g of soy protein or 100 mg of isoflavones per day.
So the average Japanese person is eating 6-11g soy protein (25-50 mg of isoflavones) and less than 10% get 25g soy protein (about 100 mg of isoflavones per day).
This is tiny compared to the amount of soy lifters would have to consume if they need to meet their protein requirements. We cannot say someone eating 150g of soy protein a day is “safe” because 10% of Japan eat 25g soy protein per day.
The fermentation argument
Some people claim that fermenting soy products makes them safe to eat and that “all traditional consumption of soy is from fermented products”.
Fermentation is useful because it reduces the anti-nutritional factors in soy (discussed in the piece on protein quality) but it doesn’t reduce phytoestrogen content in the food.
In fact it actually deconjugates some of the isoflavones into their free bioavailable form. It actually enhances the estrogenic effects.
The influencer type “scientific studies” arguments
Influencers tend to be people who have very extreme end opinions. Whether they need to do it to get attention or whether extreme people are naturally attracted to public platforms is a topic for a different article.
The pro-soy influencers seem to think you can eat as much soy as you want and it would have no negative effects on the body. Some of them even claim that soy will have protective effects on them.
They take studies on a prima facie level without considering that studies are often directly or indirectly funded by certain beneficiaries.
The mass manufacturing food industry greatly benefits if they can get the public to like soy. Unlike milk protein, soy is cheap and shelf stable.
The tobacco industry did this massively. They even set up research committees to produce pro-tobacco research. They paid off scientists to act independent while making pro-tobacco studies.
Just one such front organization called Center for Indoor Air Research funded at least 244 published studies many of which even got peer reviewed.
The sugar industry did the same thing. They tried to promote dietary fat as the cause of heart disease while downplaying the role of sugar.
It seems very obvious at least to me that the soy industry is likely to do the same thing.
Here’s a curious piece of conflict of interest found on one of the major pro-soy studies:
At least these guys are honest enough to mention the conflict of interest. There are probably many scientists getting paid off who do not disclose their relationships (just like with sugar and tobacco).
The anti-soy influencers seem to think even a tiny smidgen of soy will crash their testosterone levels. They are worried about the estrogenic effects of soy lecithin found in tiny amounts as a preservative in many foods (IMO these guys are borderline retarded).
Both of these groups have pre-formed opinions and then look for studies that support their existing opinion.
I’ve even seen some influencers share this study of a 54 year old man who drank a liter of soy milk for 3 years and developed gynecomastia and erectile dysfunction.
There are plenty of 54 year old people who developed erectile dysfunction and gynecomastia in the last few years without ever touching soy. Does this mean not eating soy causes these problems?
Or could it be a myriad of other factors like him being old, inactive, missing other nutrients in his diet like saturated fat or some vitamins and minerals, or high stress levels or something else affecting his natural testosterone production?
You know there’s a reason why proper studies have larger sample sizes and control groups…
When it comes to nutrition, the extreme opinions are almost always wrong. The biggest exception to this rule is partially hydrogenated fat (trans fat). It is undebatably trash.
Also I should mention here that animal research very often does not translate to humans. They have different metabolic pathways and metabolites among other things. Just because something is good or bad for a mouse does not automatically mean it is good or bad for a human.
So now what?
This should make it clear why soy is so controversial.
For the rest of this article, I will do a full assessment of the data and then make some conclusions. The goal is to help you understand if soy is truly a risky substance, or if it’s completely safe, or somewhere in the middle (perhaps there is a dosage beyond which it becomes unsafe?).
Let’s get to it.
Isoflavones in Soy
There are 3 main isoflavones in soy:
- Genistein
- Daidzein
- Glycitein
They act as both antioxidants and anti-inflammatories in the body along with their phytoestrogenic effects.
Here are the amounts of isoflavones present in many commonly consumed soy products. I also picked some non-soy foods for reference.
Isoflavone content in 100g of various food products
| Food product | Genistein (mg/100g) | Daidzein (mg/100g) | Glycitein (mg/100g) | Total isoflavones (mg/100 g) |
| Edamame (raw green soybeans) | 20.34 | 22.57 | 7.57 | 48.95 |
| Tofu, raw, regular, prepared with calcium sulfate | 8.56 | 12.99 | 1.98 | 22.73 |
| Tofu, salted and fermented (fuyu) | 20.72 | 23.83 | 4.95 | 48.51 |
| Defatted Textured soy flour (Soy chunks are made from this) | 67.69 | 89.42 | 20.02 | 172.55 |
| Soy protein isolate | 30.81 | 57.28 | 8.54 | 91.05 |
| Mung beans (raw) | 0 | 0.09 | 0 | 0.09 |
| Raw broccoli | 0.04 | 0 | 0 | 0.04 |
Note that these figures are averages. The actual amount of isoflavones differs by various factors like season. Check the database listed to see the standard deviations and min/max content found.
Glycitein only makes up about 5-10% of the total soy isoflavones and is much weaker than the other two, so I’m going to ignore it to keep things simple (most nutrition research ignores glycitein as well).
[TECHNICAL STUFF STARTS HERE – FEEL FREE TO SKIP TO CONCLUSIONS]
Digestion and Bio-availability of isoflavones
Isoflavones in soy occur in two main forms: free aglycones (the base isoflavone structure) and conjugated glycosides (aglycones bound to a sugar molecule).
Free aglycones are bioactive and bind with receptors while the conjugates have negligible impact.
Most of the isoflavones in soy are conjugated (Fermentation frees up a big portion of them). After ingestion, the conjugates are broken down by intestinal enzymes and release free aglycones (Genistein, Daidzein, and Glycitein) in the bloodstream.
There is a lot of individual variability. Some people have a gut microbiome that turns Daidzein into S-equol which is much stronger than Daidzein. All this individual variability makes it hard to study the effects of soy consumption in human.
People who come from high carb eating cultures are more likely to possess this equol producing gut microbiome. Estimates are 20-35% in western populations and 50-60% in Asian populations. Estimates for vegetarians tend to be even higher.
Much of these free aglycones then end up in the liver and are rapidly re-conjugated in the intestinal walls and the liver (50-60% glucuronides and 20-30% sulfates).
It’s hard to know the exact impact this has because there are many tissues in the human body that de-conjugate the isoflavones and free them up to bind with the receptors.
This is further complicated by the fact that some of these re-conjugated isoflavones end up back in the intestines and are fully broken down by the gut bacteria.
How much of the isoflavones end up being absorbed
As explained in the previous section, there is a ton of individual variability and lots of different factors so the best we have are rough numbers.
Excretion
We know that typically 20–55% of daidzein and 5–30% of genistein from a given dose are recovered in urine within 24–48 hours. Different studies show different amounts which means there’s a lot of individual variability here as well.
We do know that almost all the urinary excretion is conjugated (which hints that the free form manages to bind to the receptors).
Fecal excretion of intact isoflavones is minimal (only a few percent).
Degradation in the gut
We know a chunk of the isoflavones also get degraded in the gut and lead to no estrogenic activity (because the degradation process creates something called O-DMA which we can find in the poop).
Although for how much gets degraded, I couldn’t find reliable numbers. There is one study that claims it’s 85% but it’s not free to access and the wording they use is ambiguous “soybean milk isoflavones seem to be 85% degraded in the intestine” so it’s not clear how much we can trust the number.
It’s probably highly individual like the other stuff as well.
Some terms you need to know
Like in the previous piece, I need to give you some more background information about the human body. Read the previous piece because you will need the knowledge to make sense of this piece (don’t worry, it’s easy reading).
Ligand: Anything that can bind to a receptor is called a ligand.
Affinity: How well/tightly it binds to a receptor. Think of it like a magnet pulling a metal. Stronger pull means higher affinity.
Affinity determines how many receptors get occupied.
Efficacy: How well it activates the receptor. Think of it like how fast a motor spins when plugged into power.
Efficacy determines how big of a response you get from each occupied receptor.
Potency: It determines the practical “dose” needed to achieve an effect.
It is measured using a combination of efficacy and affinity (there are other factors too).
Think of it as how many seconds a drill takes to tighten a screw. It depends on how fast the drill spins (efficacy) and how well it fits into the screw-head (affinity, where a loose slippery fitting drill will take longer).
Full agonist: Binds and produces the maximum response.
Partial agonist: Activate the receptor but produce less than the maximal response.
Inverse agonists: Bind to the receptor and reduce its baseline activity.
Antagonist: A type of ligand that has affinity but no efficacy (binds to the receptor but doesn’t activate it).
Assay: A lab procedure used to measure quantity or quality of the target substance.
The Estrogen Receptors in the Human Body
Note: This section has been simplified so people unfamiliar with the topic can understand it.
There are two classical estrogen receptors in the human body.
| Receptor | Estrogen Receptor Alpha (ER α) | Estrogen Receptor Beta (ER β) |
| Also known as | Estrogen Steroid Receptor gene 1 (ESR1) | Estrogen Steroid Receptor gene 1 (ESR2) |
| Dominant locations | uterus, breast, liver, adipose tissue, and certain brain regions | ovary, prostate, lung, vasculature, immune cells, and other brain regions |
| What it tends to do | Regulates metabolism, bone density, and many brain circuits linked to reproduction and energy balance, and drives growth and development of female reproductive tissues. It’s the main target of most estrogen therapies and many breast-cancer drugs. | Fine-tunes or counterbalances ER-α signals (e.g., it can slow cell proliferation), supports fertility, modulates inflammation, protects nerves, and helps maintain vascular and immune health. |
To put it in simplified terms, ER-α is anabolic when activated and accelerates growth (in case of bone tissue it protects against loss) while ER-β reins in ER-α signals (acts like a brake to the accelerator).
An example of these two working in sync would be ER-α sending signals to grow a tissue, and ER-β making sure it doesn’t lead to the formation of a tumor.
Binding Preferences
The fact that there are multiple estrogen receptors tells you that the quantity of estrogen (or compounds that mimic estrogen) are not the full story.
Something that predominantly triggers ER-α will have different results from something that predominantly triggers ER-β will have different results from something that triggers both.
Estradiol (E2) binds to both receptors with high affinity. There is no subtype preference.
Estrone (E1) is a much less potent ligand than E2 shows a preference towards ER-α. The affinity is 3-4 times higher than for ER-β.
The Behavior of Isoflavones
Genistein and Daidzein both have structures that resemble Estradiol (E2). Recall that E2 is the most abundant and potent estrogen in humans.
This means they can bind with the estrogen receptors in the body and weakly mimic actual estrogen.
But what does that actually entail?
Affinity
Do the isoflavones bind to both receptors (the brake and the accelerator) equally or do they have a preference?
The main research that I could find that looked into it shows that both Genistein and Daidzein preferentially activate ER-β (the brake). This is very distinct behaviour from the natural estrogens E1 and E2 in the body.
Table comparing Relative Binding Affinity (RBA) of Soy isoflavones with E2 Estrogen
| Compound | RBA ER-α (%) | RBA ER-β (%) | ER-β vs. ER-α Selectivity |
| Estradiol (E2) | 100 (reference value) | 100 (reference value) | 1 (binds equally to both) |
| Genistein | 0.02 | 6.8 | 324 |
| Daidzein | 0.003 | 0.051 | 17 |
| S-equol | 0.144 | 3.5 | 24 |
Note: About 30-50% of people have gut bacteria that can process Daidzein into something called S-equol (a much stronger phytoestrogen).
In simple words, soy isoflavones strongly prefer binding to the beta estrogen receptors (the brakes) than to the alpha estrogen receptors (the accelerator).
Efficacy
Once bound to a receptor, how well do the isoflavones activate it? This is measured as Emax.
The data for isoflavones efficacy is much less clear and is an area of active research.
Estradiol (E2): This is the reference value. E2 produces maximum receptor activation (100% efficacy (full agonist). So Emax = 100%.
Genistein: Shown to be a full agonist in receptor assays. In simple words, it can reach E2’s max response (100% efficacy). However in realistic situations it is typically partial and taken at ~50–80% of E2 on ER-β, and lower on ER-α (often ~20–40%).
In some artificial lab conditions, very high doses can turn it into a super-agonist (achieving even higher gene expression than E2).
Daidzein: Shown to be considerably weaker than Genistein in assays. Roughly ~20–40% on ER-β and <20% on ER-α in many systems.
S-equol: Has similar efficacy as Genistein.
Potency
This is relatively easy and straightforward to measure. It combines the effects of affinity, efficacy, and a myriad of other factors like receptor stability, etc.
Below is a table comparing the dosage needed to get 50% of gene stimulation (called EC50 – Half Maximal Effective Concentration).
Note that this is the quantity needed to get 50% of the ligand’s own maximal effects.
The less you need, the more potent the substance is.
Table comparing EC50 gene stimulation by Estrogen and Soy Isoflavones (doses in nM)
| Compound | EC50 ER-α (nM) | EC50 ER-β (nM) |
| Estradiol (E2) | 0.02 | 1.67 |
| Genistein | 24 | 4 |
| Daidzein | 200 | 50 |
| S-equol | 14 | 1.4 |
[END OF TECHNICAL SECTION – CONCLUSIONS BELOW]
Phytoestrogens behave differently from regular estrogen
Estrogen receptor beta (ERβ) was only discovered in 1996. Prior to that the controversies about soy were just about potency compared to actual estrogen.
As we now know it is not just about how potent an isoflavone is to E2 but also that it prefers one receptor more than the other that plays a role in how it behaves. Isoflavones prefer binding to ER-β and behave differently to both E1 (prefers binding to ER-α) and E2 (binds equally to both).
Something that complicates the issue even more is that tissue behaviour depends not only on which receptor the substance prefers binding to but also the ratio of activation between the receptors. This makes it very hard to draw any strong conclusions with the data that we have.
It is possible that more estrogen receptors could be discovered in the future and might complicate the issue even more.
To put it simply, the long term effects of very high phytoestrogen consumption are unknown.
Soy isoflavones do not behave like regular human estrogen. This does not inherently mean bad effects. For example, soy has been associated with reduced risk of prostate cancer in men. Which seems to make sense because ER-β is dominant in the prostate and isoflavones prefer to bind to it (recall that ER-β fine tunes and suppresses the effects of ER-α and acts like one type of tumor growth control).
High consumption safety is very debatable
A recent (2021) meta analysis of studies on men shows that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects male hormone levels (total testosterone, free testosterone, E2 and E1).
If you are pro-soy, you will find studies supporting your view if you look for them.
On the other hand there is also plenty of research that shows that consuming high amounts of soy based foods leads to bad outcomes for men.
Some studies show high soy intake was associated with low sperm count. Note that correlation does not imply causation.
Another study showed that 120mg/day of isoflavone consumption every day for 6 weeks lowered serum testosterone. At the same time they saw significant improvements in the markers for oxidative stress (showing the anti-oxidant effects of the isoflavones).
In yet another study, men in good health were given 2 scoops of soy protein isolate (56g) every day for 28 days. Serum testosterone decreased during the 4-week use of soy protein powder and increased within 2 weeks after we discontinued soy protein powder.
However when you look at the actual study everything seems very mixed and the testosterone decrease is coming from one guy who had sky high testosterone levels that dropped hard after the soy intake and then dropped even more after soy was stopped and kept dropping.
So the anomaly affected the overall results.
Other than for that 1 guy, the data is very mixed. There are some people for whom testosterone improved at the end of 4 weeks of eating soy, some for which it remained the same, and some saw a decline.
So the data is too mixed and debatable. There’s no control group either sadly.
Practical Recommendations Regarding Soy Intake
All of this brings me to my practical recommendations on soy intake.
In some societies they traditionally eat soy, but not nearly as much as guys on the internet seem to think.
As mentioned earlier in the piece, the estimates are around 50 mg of isoflavones per day with only 10% of Japanese eating ~100 mg of isoflavones a day.
This is not a lot of soy. 100g of fermented tofu or 25g soy chunks and you get the 50 mg of isoflavones. The idea that Asian societies are eating tons of soy day in and out seems like a nonsensical internet invention.
Most of the studies show that consuming ~50 mg of isoflavones per day will have no real effects on your hormone levels. We can take 100 mg of isoflavones as a reasonable upper limit.
Practically, this means that there is no need to go out of your way to avoid soy. If you eat a protein bar or two with soy protein every day, you are going to be 100% fine.
50-100 mg of isoflavones seems like the dose where you get whatever anti-oxidant properties they have while minimizing the downsides.
Quite honestly, I don’t really see why someone would go out of their way to eat lots of soy products (other than budget or dietary restrictions). That there are so many other high quality food groups available that don’t have all these issues that you can choose from.
That said the protein quality is pretty good for a plant product and reasonable consumption is not going to give you man boobs.
Advice for guys on a budget and vegans
If you’re broke and soy protein is all you can afford, or if you’re a vegan, here is how you can maximize protein while keeping the isoflavone content low.
Firstly, don’t eat soy based foods that give you little protein but a lot of isoflavones. Like soy chunks. Depending on brand and processing, soy chunks have about 100-150 mg isoflavones per 100g.
That means your 50 mg limit is going to be exhausted in just 50g soy chunks and you only get about 25g protein from it. Not great.
Soy protein isolate seems like the best bang for the buck (both in terms of money and protein to isoflavone ratio).
Most regular soy protein isolate has about 90 mg isoflavones per 100g.
(The USDA database says of the 49 samples, the average was 91 mg, minimum was 46, and maximum was 199. There’s a lot of variation in the isoflavone content in the soybeans themselves).
2 scoops of soy protein isolate will give you about 50g protein and you will still be within your 50-100 mg isoflavone limit.
You can take 4 scoops if you want to push it to our reasonable upper limit of 100 mg. That will give you 100g protein and make it very convenient for you to get your daily intake needs met.
The safety of consuming more than that is quite debatable.
Of course if you’re eating 4 scoops of soy protein isolate, it would mean that you need to make sure you do not eat other foods that contain soy otherwise you will cross the 100 mg limit.
There’s also something called alcohol washed soy protein isolate. This has almost no isoflavones in it (0-3 mg per 25g scoop). For very high consumption, this seems like the safest bet.
Although I could not find anyone retailing alcohol washed soy protein isolate in India so I’m not sure if it’s easy to get or if it’s still cheap. If the alcohol washed version costs the same as whey protein, then I’d just buy the whey protein instead.
Addressing some other controversies about soy
Now that I have the bulk of this piece out of the way, let me also address some of the other controversies surrounding soy.
Hypertrophy difference with milk protein vs soy protein
There are some studies that showed that soy protein produces less muscle mass gain than milk protein. However the guys in these studies were eating far less total protein than our recommendations.
When the protein quantity is low, protein quality makes a big difference. Milk protein has more leucine than soy protein.
In studies where they compared milk protein with soy protein and matched leucine, there was no difference in hypertrophy.
Again, if you’re eating the amount of protein recommended in this series, none of these things like leucine matter. This has already been discussed in detail in a previous piece.
Basically the sheer quantity of protein is so high that you’re going to get plenty of leucine (and everything else) no matter what sources you get your protein from.
Soy and Thyroid
This has already been covered in detail by Lyle McDonald so I’ll just repeat his conclusions. You can read his website if you want the full analysis (this piece has become too long already)
In individuals with normal thyroid status, soy protein has no impact…
Anybody who is on thyroid medication should avoid consuming soy immediately before or after taking their medication as soy protein appears to impair absorption of thyroid medication. Quite in fact most things seem to impair thyroid medication uptake and it’s probably best to take it on an empty stomach to begin with. Individuals insistent (for whatever reason) on consuming soy near to the intake of their thyroid medication will need to increase their thyroid dose to compensate.
As well, individuals with pre-existing thyroid problems may need to limit their soy intake on a day to day basis. This is especially the case for individuals intent on reducing their sodium intake. I’d mention that women are far more likely to have thyroid problems than men which makes them at a higher risk for the particularly bad combination of too much soy and too little sodium/iodine.
Soy for infants
Personally given all these issues with soy and that the proper development of children relies heavily on their endocrine system, feeding infants soy based formulas is a real dumb thing to do.
Selling soy based infant formula should be illegal until we have clear research that establishes that it is safe. At the moment you are just gambling with your child’s long term health by giving them soy.
And that’s everything I have to say about this subject.
In the next piece, I’ll talk about collagen.
Your man,
Harsh Strongman
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