[toc]It’s something you’ve probably heard your entire life, or at least it seems like that. Everyone hates on Glycine max.
That’s the scientific name for soybeans, which many believe to be the world’s oldest cultivated crop.
So we have been eating it for thousands of years, but should we be?
Why soy is bad for males?
It’s a myth that soy increases estrogen in males. Eating tofu or drinking shakes made with soy protein isolate will not cause your body to produce more estrogen (or testosterone). That’s true regardless of gender.
The reason people say soy is bad for you is because it contains what are known as phytoestrogens. These are plant-based compounds which are similar in structure to human estrogen, 17-ß-estradiol, but are not the same thing. They are present in both conventionally grown and organic soybeans. In high amounts, they may be unhealthy.
The three most studied and prevalent types of phytoestrogens in the human diet are isoflavones, lignans, and coumestan.
Soybeans are the food with the most isoflavones.
On a volume basis, isoflavones represent over 99% of the phytoestrogen content in soy. (1)
Within the isoflavones category, there are different types. Among them, genistein and daidzein are believed to be the most potent. (2)
Because phytoestrogens, like the isoflavones in soy, are so molecularly similar to actual estrogen, many scientists believe they may fit and bind into the body’s estrogen receptors. Hence, even though they are not estrogen, they may mimic the effect of the real thing.
How much soy is bad for a man?
Despite being discovered nearly one hundred years ago, it’s still unknown as to whether or not phytoestrogens produce hormone-mimicking effects in humans and animals.
For that reason, definitive statements about soy being bad for you or causing man boobs (gynecomastia) are speculative and opinion-based. Because of that, it’s hard to say how many servings of tofu, tempeh, and soy milk you can consume, or how many grams of soy protein per day is safe.
Japanese adults consume an average of 7-10 grams of soy protein every day, which represents 10% of their daily protein intake.
In Shanghai, men eat 12-13 grams of soy protein per day (15% of total).
In both Japan and Shanghai, the top quartile, which is 25% of the population, eat an average of 15-20g of soy protein per day. That’s equivalent to eating a half-block of tofu daily, which is 8.2 ounces (232g).
In all of these populations, testosterone lowering and other adverse side effects have not been seen in boys, men, or women. At least according to any major, large-scale population study. (3)
However, there have been a few individual patient case studies which accuse soy intakes of roughly that amount or less causing adverse effects in males, such as gynecomastia or tenderness around the nipples. (4)
If the isoflavones in soy do have a biological effect, most likely young males are most susceptible. That means the safe amount for boys and teens may be different than of adult men.
Out of an abundance of caution, some scientists and dietitians suggest males of all ages should limit soy to an average of no more than 1-2 servings per day. Those opinions are based on the average amounts of isoflavones in typical soy foods and how they compare to the amounts safely seen in observational population studies, patient case studies, clinical trials, and in vitro (lab) data.
Many soy-based meals, such as a large tempeh scramble or a plate of tofu stir fry, contain 2-4 servings. You may want to limit those to every other day.
That’s different than say, an 8 ounce glass of soy milk, which more accurately represents a serving as per its nutrition facts label.
While it may be perfectly safe to eat vastly higher quantities, even several servings per day, the advice of 1-2 servings per day on average does seem prudent and reasonable given the unknowns. If no other benefit, at least it encourages a diversified diet that’s not reliant on one food (soy). (5)
It is possible that the isoflavones in soy may interact with estrogen receptors, though the latest evidence suggests that if it’s happening, the effect is mild.
Genistein, which is probably the most potent type of isoflavone, only appears to have a max binding affinity of 5% for estrogen receptor alpha and 36% for the beta. For daidzein, it’s merely 0.015% and 0.13%, respectively. (6)
(7)
That’s based on lab research. It’s not proven that these interactions are occurring at the same rate in living and breathing humans.
The risk, quantified
The definition of risk is the possibility of danger, harm, or loss.
Since the verdict is still out as to whether phytoestrogens in any amount are dangerous, you can’t really quantify the odds of you being harmed by eating X amount per day, week, etc.
However, you can quantify the risk on a relative basis.
Meaning, if they are harmful, how does the amount in soy compare to amount found in other foods?
What follows are the top 10 phytoestrogen foods. Or at least, based on the current science, because there may be unidentified phytoestrogens lurking elsewhere.
| The 10 highest dietary sources of phytoestrogens (measured in micrograms per 100 gram serving) |
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|---|---|---|---|---|---|
| Coumestrol | Isoflavones | Lignans | Total Phytoestrogens | ||
| 1. | Flaxseeds | 46.8 | 321.4 | 379,012.3 | 379,380.4 |
| 2. | Soybeans | 1.5 | 103,649.3 | 269.2 | 103,920.0 |
| 3. | Soy nuts | 37.1 | 68,571.5 | 122.2 | 68,730.8 |
| 4. | Tofu | 0.7 | 27,118.5 | 30.9 | 27,150.1 |
| 5. | Tempeh | 0.6 | 18,277.7 | 29.6 | 18,307.9 |
| 6. | Textured veggie protein (soy) | 2.4 | 16,122.2 | 99.4 | 16,223.9 |
| 7. | Miso paste | 2.4 | 11,131.0 | 63.9 | 11,197.3 |
| 8. | Soy yogurt | 0.5 | 10,227.8 | 46.6 | 10,275.0 |
| 9. | Soy protein powder | 0.5 | 8823.8 | 16.5 | 8840.7 |
| 10. | Sesame seeds | 0.4 | 10.5 | 7,997.2 (excludes sesamin) | 8,008.1 (excludes sesamin) |
| Source: Phytoestrogen content of foods consumed in Canada, including isoflavones, lignans, and coumestan (8) Year: 2006 Authors: Thompson, L.U., Boucher, B.A., Liu, Z., et al. Publication Name: Nutrition and Cancer Publication Details: Volume 54, Number 2, Pages 184-201. The 50 highest sources are reflected above. You may purchase/access the report here consisting of 191 foods in total, which includes granular details for each such as the types of lignans and isoflavones as well as a breakdown of their amounts (formononetin, daidzein, genistein, glycitein, matairesinol, lariciresinol, pinoresinol, secoisolariciresinol). |
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While it’s true that soybeans and foods made from them dominate the list, they’re not the worst.
Flaxseeds and flaxmeal are potentially worse for men than soy protein or any other soy-derived food. Flaxseeds have over 250% more phytoestrogen content than soybeans. When compared to tofu, the amount is 1,300% higher.
How much phytoestrogens there are in pure soy protein isolate powder is relatively low; 8,840.7 micrograms per 100g (3.52 oz). That’s less than 1/10th the amount found in soybeans. When compared to flaxseeds, soy protein has almost 98% less.
In short, the phytoestrogens are most concentrated in other parts of the bean, not in their purified amino acids.
However, the biggest elephant in the room is not soy vs. flax. Nor is it comparing soy to other phytoestrogen food sources, like real licorice.
The biggest question you should be asking is how about the actual estrogens you are eating?
That’s right.
Forget for a moment the quasi-shaped molecules in soy which kind of look like estrogen under a microscope.
Shouldn’t you be more concerned about the actual dietary sources of real estrogen in your diet?
Animal-based foods, particularly milk and dairy, contain actual hormones. There’s not phytoestrogen but literal estrogen in milk, cheese, and whey protein. (9) (10) (11)
Furthermore, whichever of the roughly 5,000 mammals you’re referencing, milk is meant to serve one purpose; spur the growth of a mother’s newborn.
It’s not meant to feed their grown offspring.
You don’t see adult cows sucking on the lactating mammary glands of females.
Nor do you see any mammal sucking on the breasts of a different species, regardless of their age!
Whether or not milk has added hormones is somewhat a moot point, because dairy is naturally chock full hormones, which includes estrogen, and other compounds intended to spur the newborn’s growth. That includes IGF-1 for fattening them up, because their metabolism can support it.
Yours can’t. You’re an adult.
Should a man eat soy protein?
Yes. Given the lack of empirical evidence that phytoestrogens in soy-based foods affect hormone levels like testosterone, there’s no good reason for males to avoid soy protein sources altogether. Less-refined sources like tempeh are quite healthy for you. The exception is protein isolate made from soybeans, because hexane and other solvents are often used to make it. The chemical residue may be bad for you.
Therefore the best reason for avoiding protein isolate from soy has more to do with how it’s made, not because of the natural ingredients it contains.
That said, given the possibility of phytoestrogens binding to estrogen receptors in the body, it’s certainly not a bad idea for men to limit the amount of soy-rich foods they consume.
Forgoing them militantly is overkill though.
However, bodybuilders and athletes may not want to be drinking scoops of the powder several times daily.
That holds true for both men and women. You don’t want the possibility of upsetting the delicate balance of your endocrine system.
Speaking of balance, men need estrogen too.
Both sexes have and need estrogen and testosterone. It’s all about having the right balance for each sex.
In fact, men can have too low of estrogen and according to a recent study put out by researchers at Massachusetts General Hospital in Boston, low estrogen in men leads to higher body fat, cardiovascular disease risk factors, and type 2 diabetes.
Plus – get this – too low of estrogen decrease a male’s libido and contributes to sexual dysfunction, like erectile dysfunction (ED). (12)
The best proteins for athletes
Soy protein is better than whey protein. In higher amounts, like for weightlifters and endurance athletes, it would be better to supplement with a plant-based source which has little to no phytoestrogen content. Just to be safe, since you’re probably using a lot.
Here are Superfoodly, the vegans use Sunwarrior organic brown rice protein on a daily basis. The natural flavor, without stevia or sugar. It’s the least chalky and gritty of all the plain rice powders on the market.
For something that’s sweet and creamy, even with plain water, consider Nuzest. They make it from European golden peas and they sweeten with thaumatin.
Thaumatin is a relatively rare non-glycemic sweetener from an African plant. It’s way better than stevia and doesn’t have the safety concerns as stevia does. The only reason it’s not more widespread is because it’s still very expensive, due to limited supply.
Our favorite flavor is the coffee-coconut MCTs. Above is what it looks like when we mix it with just plain water and a spoon. It’s very creamy with absolutely zero chalkiness or gritty texture. There’s 19g of protein for 90 calories, with 0g of sugar. We buy it on Amazon all the time, to ensure it’s always on-hand for post workout.