Soy and soy protein - does it make you more feminine?

Years of research reveal new insights

The health effects of soy have been debated back and forth for years. Bodybuilders, bio-hackers and nutrition scientists tend not to have a positive view of plant-based soy protein. Most consumers, on the other hand, assume soy is basically a wonder protein, especially for vegetarians and vegans.

So is soy a "bad protein" or not? Let's look at the latest research findings.

Concerns about soy protein

Soy contains plant chemicals known as isoflavones, which function as endocrine disruptors. These isoflavones are genistein, daidzein and glycitein. There's also a fourth one, equol, which doesn't occur naturally in soy. It's a particularly potent metabolite of daidzein that only forms in 33-50% of people, those who carry a specific strain of gut bacteria needed for the conversion (1).

These isoflavones can affect our cells in two ways. Either they bind to specific cell receptors in the nucleus, which then attach to the DNA, triggering protein transcription. In effect, they work like a weaker form of estrogen.

Alternatively, they can simply bind to the receptors and block real estrogen from taking its usual "parking spot," thereby preventing protein transcription.

Especially if you're a man, you don't want the first scenario to apply to you. At least according to the theory. Estrogen, or a weaker version of it, is believed to be responsible for "feminising effects." That's also said to make it harder to build muscle.

If you're a man with an already high estrogen level, you obviously wouldn't mind these isoflavones taking estrogen's place, since they're weaker. The isoflavones would prevent the real, stronger estrogen from binding and triggering protein transcription. This would prevent possible side effects such as extra body fat, gynecomastia, and reduced sperm count and testosterone levels.

If you have a low estrogen level, however, the isoflavones could lead to unwanted estrogenic activity.

Does soy make you more feminine? What does the research say?

Since 1946 we've known that isoflavones can trigger reproductive disorders. It was found that sheep grazing on red clover (which has high levels of plant estrogen) became infertile. Researchers made a similar discovery 20 years later, when stall-fed cows that were also fed red clover became infertile too. Not much later, the same problem was found in cheetahs. In all three cases, fertility was restored once isoflavone intake was reduced.

In countless experiments with mice and rats too, almost all studies showed that isoflavones led to reduced fertility, lower sperm counts and lower testosterone levels. Granted, in most of these experiments the genistein doses given were probably about 5 times higher than what we'd consume through our diet. Still, we need to take the results seriously, since our reproductive organs are very similar. The same hormones are involved.

In a study of 99 men, those who had consumed the most soy over the previous three months had the lowest sperm counts (2). Another study also linked testosterone concentrations to soy protein.

A study by the "American Society of Reproductive Medicine" reported that among men with already limited fertility, those who ate the most soy had 41 million fewer sperm per millilitre than those who consumed no soy (3). What's concerning is the amount of soy consumed, it corresponded to only about half a tofu patty.

To be completely honest, though, human studies on the testosterone-reducing effects of soy have been inconclusive. Some showed a positive association, some none at all. Until 2009, when a large study was published that summarised the findings of 32 separate studies on soy intake and testosterone (4):

No notable effects of soy protein or isoflavones on testosterone, SHBG (a steroid hormone-binding globulin), free T, or FAI (free androgen index) were found. The results suggest that neither soy products nor isoflavone supplements have a measurable impact on bioavailable testosterone concentrations in men.

Or does soy affect testosterone levels after all?

Why soy protein and soy isoflavones affect the fertility of other mammals but not us humans could have several explanations.

The dosages used in human studies are inconsistent. The amount of isoflavones contained depends on the type of soybean and the growing conditions, soil composition, rainfall, sunlight, etc. all play a role. Some studies probably used potent soybeans, some weak ones, and some used isolated isoflavone extracts, which led to very different results.

As mentioned, equol is a metabolite of the soy isoflavone daidzein, and it doesn't occur in every person. So it's quite possible that a notable number of the test subjects didn't have the required bacterial strain and were therefore "immune" to soy protein, which calls the entire study into question.

Soy has other downsides too

While we still don't have conclusive results on whether soy has estrogenic effects on men, there's plenty of other research that casts soy in a bad light.

1. Bodybuilders may want to avoid soy, especially soy protein isolates, under certain circumstances, since soy protein could increase protein breakdown in skeletal muscle (5). When pigs were fed casein and soy protein over a period of 15 weeks, it was found that the lower quality of the soy protein caused a hormonally driven upregulation of muscle protein breakdown.
2. A 35-year Hawaiian study of 8,900 Japanese men and 500 of their wives linked soy consumption (specifically tofu) with brain aging, shrinkage, and the development of Alzheimer's (6).
3. Unfermented soy (tofu, soy milk, ice cream, yoghurt, soy protein isolate) contains high amounts of phytic acid, which blocks the absorption of minerals such as calcium, magnesium, iron and zinc.
4. Soy is a goitrogen, meaning it suppresses thyroid function and iodine uptake, which is necessary for proper thyroid function (7).

Soy is still a bad protein

It's not realistic to completely banish all soy products from our diet, since it's used in so many products. In fact, soy makes up nearly a fifth of the calories consumed in the US. And even if that number may be lower here, it still shows just how widespread the use of soy is.

As a vegan and personal trainer in Zurich, I make a point of eating as little soy protein as possible. Here are my suggestions for you:

• If you're a man, try to avoid soy as much as possible.
• If you're a bodybuilder, look for other protein sources besides soy protein. There are numerous better (also plant-based) alternatives such as rice, pea and hemp protein. If it absolutely has to be soy, at least choose organic soy protein.
• Pregnant women should steer well clear of soy and avoid soy-based baby food.

If you're ever unsure about what's actually healthy and what's a myth, feel free to send me an email. As part of my personal training in Zurich, I create an individual training and nutrition plan for you and answer all your questions.

References:

1. Kenneth D. R. Setchell Nadine M. Brown Eva Lydeking-Olsen, "The Clinical Importance of the Metabolite Equol – A Clue to the Effectiveness of Soy and Its Isoflavones. The Journal of Nutrition, Volume 132, Issue 12, 1 December 2002, Pages 3577–3584.
2. Konkel, Lindsey, "Could Eating Too Much Soy Be Bad For You?" Scientific American, November 3, 2009.
3. Jorge E. Chavarro, Thomas L. Toth, Sonita M. Sadio, and Russ Hauser, "Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic," Human Reproduction, 2008 July 23.
4. Jill Hamilton-Reeves, et al. "Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: Results of a meta-analysis, "Fertility and Sterility, 94(3):997-1007; July, 2009.
5. Löhrke B1, Saggau E, Schadereit R, Beyer M, Bellmann O, Kuhla S, Hagemeister H. "Activation of skeletal muscle protein breakdown following consumption of soyabean protein in pigs," Br J Nutr. 2001 Apr;85(4):447-57.
6. Wartman, Kristin, "Not Soy Fast," Civil Eats, December 9, 2010.
7. Heather Patisaul, "The Pros and Cons of Phytoestrogens," Front Neuroendocrinology, 2010, Oct; 31(4): 400-419.