Looks like that book talks about flax seeds and soy which is a red flag for quack territory.

If flax seed and soy are so estrogenic and bad, then let’s look at the evidence.

Meta analysis of 41 studies: https://pubmed.ncbi.nlm.nih.gov/33383165/

> Sub-analysis of the data according to isoflavone dose and study duration also showed no effect. This updated and expanded meta-analysis indicates that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects TT, FT, E2 or E1 levels in men.

> neither soy protein nor isoflavone exposure affects TT, FT, E2 or E1 levels in men

I'm team science, however, I think it's important to point out that total testosterone and free testosterone are only part of the equation. You also have to look at androgen receptor sensitivity.

From the study you quoted:

> there were insufficient data to evaluate the effects of isoflavone exposure on androgen receptor (AR) expression

More research is needed.

Which health outcomes would we expect to change wrt your concern?

More research is needed in this area, however, I can tell you that testosterone is critical to a man's overall sense of well-being, and I would expect that someone who is suffering from a significant reduction in androgen receptor function and can't process testosterone normally might experience symptoms of low testosterone or Mild Androgen Insensitivity Syndrome (MAIS), even if their testosterone levels are normal. So, to answer your question, we're talking about depression, suicidality, anxiety, lack of confidence, lack of motivation, fatigue, decreased endurance, decreased muscle mass, increased body fat, cognitive impairment, erectile dysfunction, low libido, male infertility, gynecomastia, and in the most extreme cases, possibly even gender identity issues. People who have MAIS don't always have all of these symptoms. Some people with MAIS have no symptoms at all! It's incredibly complex, and I think it's safe to say we don't fully understand the whole thing yet. This is an area of men's health that I think is going to get a lot more attention in the near future...

What about hops (beer)? I remember beer having magnitudes more than soy or flax seed.

It also turned out that gut bacteria in human keep producing the phytoestrogen from beer days after consumption. [0]

[0]: https://pubmed.ncbi.nlm.nih.gov/15826034/

To my knowledge, soy has never been considered estrogenic because it affects levels of endogenous hormones, but because soy isoflavones directly agonize estrogen receptors.

"Isoflavones are phytoestrogens with potent estrogenic activity; genistein, daidzein and glycitein are the most active isoflavones found in soy beans. Phytoestrogens have similarity in structure with the human female hormone 17-β-estradiol, which can bind to both alpha and beta estrogen receptors, and mimic the action of estrogens on target organs"

https://pubmed.ncbi.nlm.nih.gov/23161396/

Everything changes everything in the body all the time. We only care about when things change in certain ways for certain endpoints to certain degrees.

So, what are some hard health outcomes we can measure? What does the literature say about them as isoflavones are increased? Anything significant?

For example, does erection strength decrease when men eat 300g of edamame daily or something? Show me something.

I have the same questions about meat and dairy. Google "meat estrogenic" and "dairy estrogenic". I don't consume either so I haven't cared to read them but you can find papers talking about it. Without looking further, you can't tell if it's something you should care about or not.