Soy Protein and Bones Don’t Mix

Optimal nutrition is crucial to keeping your bones healthy throughout your life but especially so as you get older.  It’s important then to know the effects of certain foods on your bones – do they support them or put them at greater risk for fracture? Recently, I’ve come across some new and, rather surprising, information about the effects of soy protein on mens bones. Let me tell you what I’ve learned…

Soy Protein May Up A Man’s Risk of Bone Fracture

A few years back, researchers publishing a study in the Journal of Clinical Endocrinology and Metabolism, reported that low levels of estradiol and testosterone, and/or high levels of sex hormone binding globulin (SHBG) can put a man at 3 times higher risk for osteoporotic bone fracture.

Osteoporosis is a condition that softens and weakens bones and makes them more prone to fracture.  Now, many of the men in this study were 80 years old or more, but I believe this is a significant finding for any man over the age of 50 whose undergone “andropause” where testosterone starts to decrease.

Testosterone is the major, dominant sex hormone for men, and estradiol is also a sex hormone that provides sexual characteristics to both men and women.  SHBG is a protein that binds to both testosterone and estradiol in the bloodstream and cuts down on the amount of them circulating to where these hormones normally go in the body. In that way, SHBG can help regulate too high circulating hormone levels.  Similarly, too high levels of SHBG will bind more testosterone and estradiol, decreasing them further, so they’re not available to do all the jobs they do.  Protecting a man’s bones against fracture is one of the things that normal testosterone levels do.  So, the higher SHBG is the more a man’s bones are at risk for fracture.

The researchers concluded that the measurement of sex hormones, estradiol and testosterone, as well as SHBG levels in older men might help identify men at higher risk for bone fracture.  Since then, I’ve been recommending over-50 male patients have blood work measuring these hormone levels to know how high their risk is for potential bone fracture.

Now, enter a new study that came out this month, October 2013, regarding soy protein and its effect on a man’s testosterone and SHBG levels. These researchers, publishing their study in The Journal of the American College of Nutrition, studied the effects of soy and whey protein supplementation on testosterone, SHBG, and cortisol (a stress hormone) response to intense bouts of resistance exercise.

Since many male athletes and bodybuilders make frequent use of post workout protein shakes that contain either soy or whey proteins, or both, the researchers wanted to know more about the effects of each on male hormones.  They found that the male study participants who consumed 20 grams of soy protein each day for 2 weeks had a blunting, or decrease, in their serum (blood circulating) testosterone.  The upshot of this study is that the more a man uses soy protein the lower his serum testosterone will be. As I said earlier, the lower the testosterone, the more at risk a man’s bones are for fracture.

In 2 other separate research studies, one looking at how to raise SHBG to treat the condition of polycystic ovarian syndrome (PCOS) in women, it was found that the best way to raise SHBG was by using a soy supplement.  The phytoestrogens (plant equivalents to human estrogen) in soy raised SHBG levels by 30%! In the second study, researchers looked at how soy might affect men with prostate issues.   These researchers also concluded that soy products did increase SHBG and decrease serum testosterone.

So, the take away from the combination of these research findings is that men who consume soy protein products on a regular basis are going to have lower testosterone and higher SHBG levels.  As a result, they are going to be at greater risk for osteoporotic bone fracture.

There has been a lot of confusion over the effect of soy products on hormone production and balancing in both men and women.   Because they are phytoestrogens, soy products have been shown to be mostly beneficial in balancing a woman’s hormones in menopause.  But, the benefit of these phytoestrogens doesn’t cross over to males.  In fact, phytoestrogens can be damaging to a man’s system resulting in low-T and all its health complications – higher risk for bone fracture being one of them.

The results of one study doesn’t always mean that I would advise my patients to change their lifestyle, diet, etc, but when there are several studies pointing in the same direction, I may revise my recommendations.  If you’re a guy who knocks back a soy, or soy/whey protein shake after your workout, or use soy protein shakes, or bars, to supplement your protein intake, it’s probably prudent to substitute these with whey or casein protein-based shakes, bars, etc.  I want my patients, and my readers, to have the best insurance and protection against bone fracture as possible so they can lead a long, healthy, and active life without disability or impaired mobility.

Stay Well,
Mark Bromson, M.D.

Soy Guide for Men


Mark Bromson, M.D.

Dr. Bromson is Board Certified and Recertified by the American Board of Orthopaedic Surgeons, and is also certified in Age Management Medicine.

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