Soy oh soy, here we go!
There is soy much conflicting information out there about soy.
Soy what should you believe?
It can be tempeh-ting to listen to the doom sayers and scaremongers but before you cut all soy from your life, please have a listen to this episode (or at least read the transcript).
Soyly you can spare 15 minutes!
<insert tofu pun here>
Welcome back to the Bite Me Podcast. My name is Jono I'm from Bite Me Nutrition, where we make food work for you, not against you. Today, we're going to be talking about soy, which I'm sure no one's heard anything controversial about whatsoever. But just in case you have, I thought it would be really good to go through probably the three biggest topics that I feel soy comes up a lot in and talk about its influence on those things, give you the science so you can make the decision around whether or not, or how you want to include soy in your diet. Of those three areas, I would say, eproductive slash fertility nutrition, um, as well as the impact on sex hormones, but I guess more related to say body composition, you know, testosterone, estrogen affecting muscle gain and fat loss, those fertility and then body composition are probably the two biggest ones as well as whether it decreases or increases your risk of cancer. So we're going to go through, you know, reproductive hormones, reproductive health, uh, we're going to go through cancer, and we're going to go through a soy's impact on body composition.
Soy is a really high quality plant-based protein and what we mean by high quality, essentially it just means it's got all of the essential amino acids in a reasonable amount. To be honest, that's not super important if you're eating a wide variety of plant-based proteins, but it's nice to know about soy.
Uh, soy also is quite high, not, not every single soy product, but lots of soy products are quite high in various other nutrients, particularly things like fiber or iron. Um, some soy products are really high in calcium, you know, so. It's not just about the protein that there's some other great nutrients there as well. Um, but.
The controversy comes from the fact that it's also quite high in these iso flavones. And isoflavones, don't be put off by the name is just, uh, a compound that the plant has created to, basically it gives the plant its color. Um, it's also involved in lots of cell signaling and, um, I can't remember, I'm not a botanist.
I know that isoflavones, don't just give a plant there colour, there's tons of different roles that they play in that plant. So important for the plant. But. For us. Um, the reason why these things can be contentious is we then known as phyto estrogens. And the reason they're known as phyto estrogens is because they can have estrogen region mimicking effects. And so what that means is.
Estrogen is a hormone in the human body. Um, and it looks like these phyto estrogens that we get from soy can also trigger things that estrogen might trigger. So I guess the main concern comes from if we have normal amounts of estrogen, but then on top of that, we lay out heaps of phyto estrogens. Will we get these adverse effects? That would be similar to having a bnormally high levels of estrogen, which. You know, for almost everybody is not ideal. Um, and so that's largely where the contention around soy comes from.
If you haven't listened to the MSG podcast, ouch. Please go and do that afterwards. Um, but if you have, you might remember what can often happen is taking a food or a component of a food. Um, and testing it experimentally in very high doses doses that don't reflect how it's typically consumed by human beings. Uh, and also delivered in a route that is not how we would typically consume it. So rather than, you know, administering soy orally. Uh, they might do much larger doses of these phyto estrogens, and they might do it via like IVs. So, [00:04:00] you know, intravenously straight into the blood.
Um, and so always really important to look at that. There is similar to MSG some scary mechanistic data. Um, out there or some scary data in mice where they have given mice again, whose metabolisms are quite different to our own. And they've given them quite high doses of phytoestrogens and they've given them these doses kind of bypassing our stomach, small intestine, large intestine so, ignoring any impact that digestion could have on them, which is. kInd of important. So ignoring that is in my opinion, not the best move. Um, so if you are coming across really scary studies around soy, that's typically why.
I'll dive into reproductive health first, I feel like that's the area where soy comes up the most. Um, this is actually kind of how the whole phyto estrogen, estrogen mimicking effects of these. [00:05:00] iso flavones was discovered. Um, I think it was in the thirties or the forties. There was actually a flock of sheep in Western Australia that were having a different differing birth rates. Um, and they were trying to figure out why, and it turned out they were, um, grazing on a Clover that was really, really, really high in these phyto estrogens. And that. Cause people to, um, you know, look further and kind of got us to where we are today. So.
I want to preface everything I'm about to say with, unfortunately, um, particularly for fertility, good long-term specific human data doesn't really exist. Which is difficult. It means we do have to make inferences from observational data. We need to look at big groups of people and see that the people that eat more soy, do they have increased or decreased risks of certain things?
Um, and whilst that can be helpful, it doesn't always necessarily. Guarantee that yes, it [00:06:00] was the soy causing that. tHere's so many other things that could be causing that. We can still take mechanistic data into account. We can use statistical analysis to remove other variables and we can do lots of, well, not me. I suck at stats, but people much better at stats can do some fancy stats stuff to say kind of remove. Okay. Was the increase in risk of that cancer due to the soy or was it because that person smoked or was it because that person was sedentary?
And so we can get some decent data out of observational studies, but in terms of having really crystal clear solid data. I wouldn't say we're quite there yet. When looking at female reproductive health, again, looking at some observational data, there are some. That show that could be potential impacts on, uh, birth rates, lowering birth rates. But a lot of these populations of people were coming from people, um, who were struggling with fertility. So couples that were undergoing IVF.
Um, and so there's definitely that variable added there. And then on the flip side of the coin, there's actually some studies showing that people with higher rates of soy consumption, undergoing IVF had better results because of that. Okay. Um, so, and in fact, probably the, the best quality data we have, best quality study we have, there was a big meta analysis done, which is basically a study that takes a bunch of studies pools, their data. Uh, and then kind of re statistically analyzes that data with much. A much larger pool of people, theoretically. And most of the time, finding a, being able to find better quality findings.
So that found that at best, there was no impact. Sorry. That's not what I mean. At worst, there was no impact on fertility at best. There was actually a slightly positive impact on fertility. So again, we are sort of extrapolating this from, from observational data, but plenty of [00:08:00] people have extrapolated far more from far less. So.
Moving into male fertility.
Simply appears to be no real impact. And I know that this is, I mean, I. I'm a male interested in building muscle so I guess, bit of bias there. Uh, and that's the number one thing. Ah, don't guys shouldn't eat soy. It's going to feminize them, whatever the heck that even means. And it's going to, you know, blunt your ability to gain muscle. It's going to lower your testosterone. It's going to increase your estrogen.
Blah, blah, blah, blah, blah. The reality is there's no data in humans to back that up. So if you're a guy, or if, if you're someone interested in building muscle. Um, soy does not impact your ability to do that. If anything, I would argue. It's a really good thing to add, because as we mentioned earlier, it's a really high quality source of protein. High quality protein is really great for supporting muscle growth when paired with a few other things.
So the male data around its impact on muscle building, fertility rates of [00:09:00] fertility, even just testosterone levels, um, that doesn't show that there's any impact. And in some of these studies, some of these males were having very high. Uh, iso flavone uh, so very high intakes of soy and soy products that were particularly high in these.
iso flavones these phytoestrogen. So, um, it's not just a. Uh, we maybe need to check higher doses, these doses where we're pretty crazy high, which, good caveat or good a segue.
There is a case study, which gets thrown around a lot, of a male who developed gynecomastia or, I don't know if it was quite that, at least like in enlargened breast tissue, from his soy consumption, but he was drinking three liters of soy milk a day, which is so far above and beyond what we would recommend as a normal soy intake. So, if you're concerned, don't drink three liters of soy milk a day.
Anyway, we're going to talk about cancer now. Uh, so again, fairly straight up and down here. There's no evidence to suggest that soy increases cancer risk. Of anything. If anything, it actually might reduce your risk of, particularly breast and prostate cancer. Those are the ones that are quite closely linked with estrogen and testosterone.
Um, and so those are the ones that often come up when we're talking about soy is risk of cancer. But yeah, like I said, if we take the body of evidence as a whole. Uh, again, worst case scenario, soy does nothing, best case scenario, it may actually reduce your risk of these things. So look. I'm not saying, Hey, everyone should eat soy to reduce your risk of these things. The evidence, the strength of the evidence isn't there, at least enough for me to make such a strong statement, but saying like all scientists do so we, you can't nail us down. Um, It suggests that it may reduce your risk of cancers, but I'm pretty comfortable saying that based on the studies that we've got so far.
I've already gone through body comp, but there was a very specific study that showed, um, the effect of consuming soy protein versus consuming animal protein. Uh, when you take total daily calories, proper training into account. Had no impact. Uh, on the muscle built in that. So again, even if we're ignoring all of the phyto estrogen things. And we're just looking at the quality and the impact of soy protein in your diet. It appears to be no different to normal protein, as long as you've ticked everything off. So. One thing we should talk about is servings of soy per day. Right? Um, and so, a serving of soy. kInd of refers to it's iso flavone content it's phyto estrogen content. So for example, a serving of soy we would say is maybe like 250 mils of soy milk or a [00:12:00] hundred grams of tofu, 35 grams of textured, vegetable protein. Each of those is going to be providing you with. Oh, I should've done this earlier. I think it's, it's going to be providing you with about 20 milligrams of phyto estrogens.
Right. Um, and with all the studies that we've looked at. The height. Like even the higher end of. A hundred milligrams of isoflavones of a hundred milligrams of phytoestrogens per day.
We haven't seen any negative effects. So if you're keeping under, say three to four serves of soy a day, your phyto estrogen intake is going to be around the 50 to 75 milligram mark. It's going to be well under what we've seen is safe in studies so, yes, I would recommend not exceeding that four servings five servings of soy a day at most. But to be honest, that's not just about the phytoestrogen content, that's just about, you know, dietary diversity and how we should be aiming to get our protein and our other vitamins and minerals from a wide variety of not just soy-based sources so we can get all of the good stuff.
Right. So, Yes, pay attention to the servings of soy that you're having. It's still like, like four servings of soy a day is, is, is pretty intense. So it's unlikely you're accidentally exceeding that. If you're not exceeding that if you're including soy as part of a well-balanced diet and you've got everything else going on, its impact on fertility sex hormones and cancer risk appears to be no, if anything, it might be positive for a couple of those. When you know, we're looking at like fertility or cancer. Again, not hand on my heart saying it will improve those things, but you know, the data is leaning that way. Um, and in terms on, in terms of its ability to, uh, whether it affects your ability to gain muscle or lose body fat,
No, it does not. If anything, it might support muscle growth. Because it's a high quality protein. So hopefully. Oh, I did not put a single soy [00:14:00] based pun in this that's a bit disappointing. I'll have to put it in the episode description. You can get all the soy-based pun there. Hopefully this has helped, um, provide a bit of clarity around soy, um, and a bit of comfort. Um, so you know that you're not killing yourself or your children and giving everyone cancer and ruining everyone's fertility by responsibly consuming soy. If you learnt something from this, I would love for you to take a photo, put it up in your Instagram stories and tag me. So, um, my ego can be stroked. Otherwise I'd also love if you would rate, review, subscribe. All of the other things that I can't remember.
And I'll catch you next time.
Episode Links & References
- Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence
- Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies
- No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise
- Soy, phytoestrogens and their impact on reproductive health
- Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis
- Soy Consumption and the Risk of Prostate Cancer: An Updated Systematic Review and Meta-Analysis
- Soy intake and breast cancer risk: a prospective study of 300,000 Chinese women and a dose–response meta-analysis
- Risk assessment for peri- and post-menopausal women taking food supplements containing isolated isoflavones
- Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature
- Meta-Analysis of Soy Intake and Breast Cancer Risk