| | Say It Ain’t Soy!

Author / Leah Kay

Nothing fires me up more than leading the charge against the massive amounts of bullshit in the nutritional world. Luckily, Power Athlete has been in the business of battling bullshit for years. Today’s topic, soy. Often touted as a “miracle health food”, discover the link between soy and performance and how it could not only be working against you in the gym but also destroying your health.

What is Soy?

Soy is a legume which is a type of plant, such as a pea or bean, with seeds that grow in long cases called pods. Soy can now be found not only in the obvious foods (soy sauce, tofu, edamame), but can even be found hidden in things like canned tuna, prepared meat (such as pre-made burger patties) and even vitamins.

soy in tuna, soy and performance

It still blows my mind that we’re continuing to have the soy argument. I assume we can blame most of it on the fact that the soy industry spends millions of dollars marketing it as the “healthy alternative” to meat or dairy with less fat and less cholesterol.(1) Or, maybe it’s because the media has decided that skinny jeans is an acceptable look for guys and they don’t care that continuing to sip their soy lattes is dropping their T levels faster than Beiber is selling records. Regardless, it’s our job to set the record straight. Soy isn’t and never has been part of the Power Athlete diet and is doing more damage to your potential gains than your high school sport coach.

SOY: Chemical Breakdown

My biggest beef with soy lies in its chemical structure. You see, soy contains phyto-estrogens, sometimes known in the literature as bioestrogens. These phytoestrogens chemically look very similar in the body as our own natural estrogen compounds and thus can disrupt our normal hormonal processes.

A recent study out of the University of Connecticut (2) looked at changes in estradiol concentrations in men utilizing either soy or whey supplementation following resistance exercise. After only 14 days, the men drinking soy were found to have lower testosterone levels and higher cortisol levels. That right there is a recipe for disaster if building muscle and increasing performance is your goal, but hard-charging athletes are not the only ones that should be worried about these results. Cortisol is a catabolic steroidal hormone that affects muscle tissue balance by increasing protein breakdown and decreasing protein synthesis.(3) Chronic elevation of cortisol can also lead to things like poor sleep and blood sugar dysregulation which in turn can result in unwanted weight gain and nobody wants that!

But phytoestrogens aren’t the only disturbing chemical compound in soy.

The soybean has one of the highest phytate levels of any grain or legume that has been studied. Grain or legume-based diets high in phytates can actually block the absorption of minerals such as calcium, magnesium, copper and zinc in the small intestines. The deleterious effects of magnesium deficiency in the Power Athlete was a recent topic of @John’s over at TTMJ. An article in the American Society for Clinical Nutrition pointed out that phytic acid was also a major inhibitor of iron absorption in soy-protein isolates.(4)  Anemia is a common problem we often see in female athletes. In fact, a 2011 study of female collegiate rowers in New York state found that 10% were anemic and 30% had low iron stores.(5) These low iron levels can contribute to fatigue, depression and most definitely poor performance.

Soy: Effect on Male Athletes

If someday producing a brood of mini Power Athletes is in your future, stepping away from the soy is even more important. Men in the highest category of soy food intake had an average 41 million less sperm/mL than men who did not consume soy foods.(6) A similar study found that an endocrine disrupting compound in soy called genistein can impair sperm as it swims towards the egg and even more surprising was that it took smaller doses of genistein to cause infertility in women than in mice.(7)

Soy and Performance

We’ve learned so far that research has demonstrated soy as an endocrine disruptor, cortisol driver, and mineral absorption inhibitor, but it’s also a piss-poor protein with regards to recovery. Regardless if you are trying to lay thick slabs of muscle, recover from your spin class or train for a 5k fun run, your body is going to need quality protein.  A study from the Journal of Applied physiology compared ingestion of whey hydrolysate, caseine, or soy protein isolate on the effects of protein synthesis. It was found that ingestion of whey protein resulted in a larger increase in blood essential amino acid, branched chain amino acid, and leucine concentrations than either casein or soy. Mixed muscle protein synthesis was 93% higher with whey than caseine and 18% higher with whey than soy.(8) Losers, soy and performance

Soy Users Are Losers

Taken together, I’d like to think we have successfully slain the soybean. It doesn’t matter if you’re a hard charging athlete looking to achieve pinnacle performance, or the person in the “masters” division trying to stay healthy, soy is NOT your friend and there is a definite negative link between soy and performance. We use our food to fuel the fire in the machine and what we eat affects very important aspects of life. If you’re leaving this article more confused than informed, then you are on your first step to enlightenment! Don’t give up, go down the wormhole. It will literally save you and your family’s life. If you don’t have time for that, head on over to our Power Athlete Nutrition programs. Here, you will find a nutrition plan that’s sure to fit YOUR goals!

1 Fallon, S. (2005, August). The Promotion of Soy – Weston A Price. Retrieved April 08, 2016, from http://www.westonaprice.org/health-topics/the-promotion-of-soy/

2 Kraemer WJ, Solomon-Hill G, et al.  The effects of soy and whey protein supplementation on acute hormonal responses to resistance exercise in men.   J Am Coll Nutr, 2013;32(1):66-74.

3 Garrett RH, Grisham CM. Biochemistry, 2nd Ed. Orlando, FL: Saunders College Publishing; 1999.

4 R F Hurrell, M A Juillerat, M B Reddy, S R Lynch, S A Dassenko, and J D Cook. Soy Protein, Phytates and Iron Absorption in Humans. American Journal of Clinical Nutrition, 1992; 56(3):573-578.

5 DellValle DM, Haas JD. Impact of iron depletion without anemia on performance in trained endurance athletes at the beginning of a training season: a study of female collegiate rowers. Int J Sport Nutr Exerc Metab. 2011 Dec; 21(6):501-6.

6 Chavarro JE, Toth TL, Sadio SM, Hausser R. Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Human Repr. 2008 23(11): 2584-2590.

7  Mercola, J. (2009, July 9). Eating Soy Can Decrease Your Fertility 7/9/05. Retrieved April 08, 2016, from http://articles.mercola.com/sites/articles/archive/2005/07/09/soy-fertility.aspx

8 Tang JE, Moore DR, Kujbida GW, Tarnapolski MA, Phillips SM. Ingestion of whey hydrolysate, caseine, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. Journal of Applied Physiology. 2009 Sept; 107(3)987-992.


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Leah Kay

Former collegiate volleyball player and 7 year competitive CrossFitter. 6x CF regional qualifier and 1x CF Games qualifier. Began coaching CrossFit in 2009 while working towards a Bachelor's in Nursing. Studied functional medicine through the American Academy of Anti-Aging in 2013 with specific emphasis on nutrition and hormone regulation. Continues to blend love of coaching and wellness as Head Trainer and Co-Owner of CrossFit Katy and Functional Nutritionist at Specialty Healthcare and Wellness in Houston, TX.


  1. Ingo "Joey Swole" B on April 22, 2016 at 2:20 pm

    Great article. I’m sharing this.

  2. Em Clem on April 28, 2016 at 6:06 am

    Great article @leahk! With the help of our head nutrition coach at CFSB, I found out about a month ago that I have severely low cortisol levels (which explains a lot!), so this was great to read. I’ve always known soy was a no-no but didn’t quite understand why – I’ve just always heard people I trust tell me to stay away from it. Given its effects on cortisol and hormonal levels, it’s definitely something I’ve started paying even more attention to!

  3. Alex McMahon on April 30, 2016 at 6:08 pm

    Finally a great write up on how crappy of a food soy is! I’m tired of people trying to debate soy being a good food.

  4. Alec Davies on August 14, 2016 at 8:08 am

    Nice work @leahk

  5. Melissa on October 18, 2016 at 3:01 pm

    Interesting….I eat soy and maintain a figure competitor stage physique 365. And I compete in the masters category, last show the judges literally stopped me mid posing to ask my age…I look THAT young, why? Soy and the rest of the plants I eat.
    I find it comical that people who don’t eat tofu, tempeh or edamame have the gall to post some weak links to studies with no backbone to stand on and claim this all to be fact.
    I didn’t eat soy for almost 30 years and now at 36 I am so lean, ripped and healthy, I am almost embarrassed to show my body anywhere except on stage and I am even more embarrassed when people find out my real age.
    Soy is a staple of the Asian diet where not only do they have the longest life spans but also the lowest rates of cancers and heart disease.
    Feel free to trash something you have NO personal experience using/eating but at the end of the day your argument is weak at best.
    And soy licthen is an emulsifier, not supposed to really be in any foods it just helps mouthfeel so blame the crappy food company’s you buy your food from for filling their products with junk. Add soybean oil to the list.
    These things are NOTHING like tofu, edamame and/or tempeh, which are amazing sources of protein, fiber and calcium.
    So to say soy is bad because you buy food with soy based fillers in it is not only ignorant it’s very reckless of someone. Add to that if you studied anti aging and DIDN’T learn about soy’s benefits…you got ripped off cuz soy LITERALLY is the fountain of youth for women.
    There is NO word for menopause in Asia…do the math.
    Whey is also a disgusting by product which is so hazardous to our bodies and the planet it cannot even be buried in the ground cuz it literally KILLS the soil, nutrients and everything around it.
    You want to put THAT into your body?
    Makes no sense. But then again, that is typical of this industry.

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