I get asked whether or not soy is good for people all the time, and I get it; there's a lot of confusion out there. You get some blogger with pseudo nutrition qualifications telling you that it'll make you sprout a second head. Others say it's a 'superfood' that can cure whatever ails ya. Based on the available science, my opinion about soy lies somewhere in the middle of these two extremes. Here's a list of questions I pulled together based on what I hear the most common concerns are with soy. And yes, a student at an Ivy League University did once ask me if soy would give him boobs.
1. What are the benefits of eating soy?
Here's what we know: diets high in soy are protective against breast cancer in women. It also appears to help protect against breast cancer recurrence in breast cancer survivors and increase survival rate. And that's not according to one or two choice studies, LOADS of studies show this. There's also some evidence linking soy with lower cholesterol levels. It can also help relieve symptoms of menopause (so you can focus on being hawt and not hot), and can reduce the risk of osteoporosis. It may also be protective against other forms of cancer, like endometrial cancer. Pretty. F'in. Sweet.
2. Are some types of soy better than others?
Prolly so. Just like with any food, the more processed it is, and the less it looks like its natural form, the less of it you want to eat. So, you probably want to swerve soy nuggets (even just typing that made me feel weird). Same goes for other fake soy meats. Look out for 'hydrolysed soy protein' on food labels too. Aside from the fact that it's highly processed, that shit has hella glutamate in it and can be a particular problem for people with MSG sensitivities.
Tofu and soy milk are the middle ground here, in that they are minimally processed. Soy milk is just soy beans (edamame) that have been boiled, blended up with water, and strained. The liquid part becomes the soy milk, and the solids that are left over usually just get thrown away or turned into soy protein isolates. Making soy milk is no different than how you make any other nut, seed, or grain milk, like almond or coconut. The problem I have with soy milk is not the stuff you make at home, but the commercial stuff you buy at the shop that has weird stuff added to it.. If you want to make your own soy milk, then go for it. Tofu is just soy milk that has been set using a coagulant, and depending on which one they use, it can actually be a pretty good source of calcium if you use the liquid for cooking (look for brands set with calcium chloride).
The best sources of soy are the least processed; edamame and tempeh. Edamame are straight up soy beans. Tempeh is a whole bunch of fancy soy beans that have been fermented into a little cake. Unlike tofu, tempeh is made using the whole soy bean. There's some evidence to suggest that tempeh may be nutritionally superior to edamame because the fermentation process makes the soy more digestible AND gives it antimutagenic properties (i.e. no growing that second head). Fermenting also has the benefit of reducing phytic acid, a compound that's present in plant foods that can interfere with the absorption of some minerals in the gut.
3. Soy suppresses thyroid function, amiright?
Not exactly, soy does indeed have a 'goitrogenic' effect in people with marginal iodine deficiency. But so do cruciferous veg like broccoli, as well as flax seed. The answer here is not to avoid these healthy foods but to make sure you have optimal iodine intake: good sources include sea vegetables (kelp, and dulse for example), and strawberries.
4. What are the downsides of soy?
So just like with anything, you can have too much of a good thing. A diet that's really, really. really high in soy can increase the levels of insulin-like growth hormone (IGF-1). This compound is a total bummer and is related to cancer and ageing. It's bad news. BUT, and I want this to be very clear, you have to eat a massive amount of soy for this to be an issue. We don't know the exact amount that will cause problems, but we can safely say that anywhere below 5 servings of soy foods PER DAY won't do any harm at all (and it's actually really hard to reach 5 servings per day). I personally think that's too high for other reasons; eating too much soy can also lead to sensitivities or even allergies. Also, if you're eating that much soy, then you're probably not eating other healthy things, you need to get some variety up in there. I'd recommend no more than a couple of servings per week.
5. But, I'm a dude?
I hear ya bro, you're worried about growing boobs, or becoming infertile. It's because of dumb scaremongering headlines like "Eating Soy Decreases Sperm Count". Truth is eating soy doesn't decrease your sperm count. BUT. It increases ejaculate volume. So although the concentration is lower, the total number of swimmers stays the same. Plus, what partner wouldn't be impressed with a large ejaculate volume? As for the boob thing, total bro-science, you're not gonna get boobs dude. Lastly, and most importantly, there's some pretty compelling evidence that soy foods can help prevent prostate cancer.
That's a lot to digest, so here's a handy little guide.
* Avoid highly processed soy foods/ingredients like fake meats and soy nuggets
* Choose fermented versions of soy like miso, tempeh, and soy sauce for best nutrition
* If you're really into tofu then get the sprouted variety
* Don't overdo it: you don't need soy up in your business every single day. Mix it up with other beans and legumes and limit soy to a couple of portions per week
* Opt for organic and non-GMO varieties where poss
And lastly, soy can be part of a healthy diet that is high in health promoting whole, plant based foods, and may even have some cool health benefits! If you have any more questions then I'd be happy to answer them in the questions or email me at hello@laurathomasphd.co.uk