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Soy: Health Food or Food to Avoid?

Part Two

by Gary F. Zeolla

This article is continued from Soy: Health Food or Food to Avoid? - Part One.

Soy Infant Formula

Among the anti-soy crowd, the use of soy infant formula seems to be particularly troublesome. The concern is soy formula will lower testosterone levels in developing infants. However, for ethical reasons, it is difficult to perform controlled studies on human infants, but such studies have been on animals.

One such study was done using marmoset monkeys. The study concluded, “Of the soy-fed baby marmosets, 80 percent had very low testosterone levels (< 0.5n/ml); only 8 percent of cows' milk formula-fed or exclusively breast-fed monkeys had such low levels” (Natural Foods). Such results do raise concerns.

However, a study reported in the Journal of the American Medical Association (JAMA) tried to put these concerns to rest. It was a “Retrospective cohort study conducted from March to August 1999 among adults aged 20 to 34 years who, as infants, participated during 1965-1978 in controlled feeding studies conducted at the University of Iowa, Iowa City (248 were fed soy formula and 563 were fed cow milk formula during infancy).” After looking at various parameters, the researchers concluded, “Exposure to soy formula does not appear to lead to different general health or reproductive outcomes than exposure to cow milk formula. Although the few positive findings should be explored in future studies, our findings are reassuring about the safety of infant soy formula” (Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood).

However, this study was not without controversy. An article titled, Experts Dispute JAMA Soy Infant Formula Study reports the following:

Dr. Mary Enig, President of the Maryland Nutritionists Association, points out that the researchers found higher rates of reproductive disorders, asthma and allergies in those who had received soy formula as infants.

"This is in line with a number of reports in the scientific literature," said Dr. Enig. "The research team glossed over negative findings and omitted them from the Abstract and Conclusions, noting only that women who had been fed soy formula reported slightly longer duration of menstrual bleeding and greater discomfort with menstruation."

Other gynecological problems, which were omitted from the main body of the report, included higher rates of cervical cancer, polycystic ovarian syndrome, blocked fallopian tubes, pelvic inflammatory disease and hormonal disorders. In addition, although the study did not specifically determine thyroid function, soy-fed females reported higher rates of sedentary activity and use of weight-loss medicines, thus adding new evidence to numerous scientific reports of soy-induced thyroid problems.

The article also reports, that “both the British and New Zealand governments have issued warnings on the use of soy infant formula.”

And an article titled, Soy Infant Formula Dangerous to Babies, Say Groups reports:

Epidemiological evidence links soy formula consumption to:

Needless to say, this is an area of great controversy, and much more research is needed. But what is not without controversy is that breast-feeding is the best option for feeding infants.

Other Proposed Benefits and Potential Drawbacks

Other befits to soy have been proposed. For instance, it is claimed that soy raises blood antioxidant levels and reduces post-workout soreness. However, as with many other proposed benefits of soy, these benefits can be attained in other ways. Soy raises blood antioxidant levels simply because it contains significant amounts of antioxidants, but so do many other foods, most notable among these are fruits and vegetables. And post-workout soreness can be reduced by the consumption of any intoxicant containing foods, like again, fruits and vegetables. Also supplemental vitamins C and E has been shown to reduce post-workout soreness.

But in regards, to vitamin E, one study I came across showed that soy can actually reduce plasma levels of vitamin E. However, supplemental vitamin E was able to correct this problem. So the study recommended, “the supplementation of vitamin E may be required in subjects with long-term and abundant intake of soy protein” (Effects of soy protein on levels of remnant-like particles cholesterol and vitamin E in healthy men).

But even more radical is the claim by Testosterone magazine that soy can damage testicular cells, increase cortisol levels (the “stress” hormone), and cause muscle breakdown (Soy is Still Bad Protein). However, I was unable to find evidence supporting these claims.

But one potential problem that is very real is soy is a common food allergen. It is for this reason that labels of soy containing foods now include a notice, usually in bold print, something to the effect of: “Contains soy ingredients.” Food allergies are a common but often overlooked cause of various health problems, so this is an important point.

Quality of Soy Protein

One last issue needs to be considered, the quality of soy protein. The quality of a protein is determined in different ways. The issues considered are how closely the amino acid breakdown of the protein matches what humans need and how well the human body can metabolize the protein. Three different scales are used for this purpose: net protein utilization (NPU), biological value (BV), and protein efficiency ratio (PER). It is not always easy to come up with exact values, so they will sometimes differ for the same foods from study to study. But the important point is the comparison between the protein sources.

Now some, mainly vegetarians, will often claim that soy protein is of as high a quality as animal proteins. However, no matter which of these three scales are used, soy is always ranked considerably lower than animal proteins. This can be seen in the following charts:







Dairy products






Natural brown rice


Red beans






White beans




Whole wheat bread


White bread


(Protein Utilization: How Much is Absorbed?)


Protein PER BV NPU Chemical Score
Whey 3.0 104 92 >100
Casein 2.5 71 76 82
Egg 3.9 100 94 >100
Soy 2.2 74 61 69

(Whey Protein: a Unique Source of Protein)







Whey Protein Isolate










Cow's Milk




















(Advantages of Whey Protein)

So soy is a higher quality source of protein than other plant proteins, but it is nowhere as high in quality as animal proteins.

And consider the following from Men's Health:
Flush that soy shake. Researchers compared how soy protein and casein protein (from dairy products) are converted into a waste product called urea. The study found that soy protein is converted far more readily into urea and eliminated during protein synthesis (how protein is turned into muscle). The article, in Human Nutrition and Metabolism, also says that protein synthesis is more than three times greater with casein protein than with soy.

My Experience with Soy

I had followed a vegetarian or near-vegetarian diet for years. Then in the summer of 2001, I switched to a full vegan diet. But shortly after that I began to develop various health problems. These are discussed elsewhere on this site. But to make a long story short, I now believe that the vegetarian/ vegan diet was a contributing factor in the development of my health problems.

One of the reasons I believe I had problems with the vegetarian and especially the vegan diet was while following such diets I consumed quite a bit of soy, especially with the vegan diet. Specifically, I began using soymilk instead of milk. I regularly ate Atkin’s Advantage Bars, in which the primary protein source is soy protein isolate. I would also regularly consume soynuts, canned soybeans, and texturized vegetable protein (TVP; made from soy and used to make imitation meat products). So I was consuming quite a bit of soy protein. But I would later find out that I was allergic to soy. I didn’t have any immediate reactions to it, but food allergies can have delayed reactions, and such delayed food reactions can be the “hidden cause” of various health problems.

Once I found out I was allergic to soy, I stopped consuming it. However, I was later treated for this allergy through NAET allergy treatments. I won’t go into details here as I do so in the articles listed at NAET Allergy Treatments and Applied Kinesiology. But the important point here is that after I was treated for the allergy to soy, I began consuming it again in the summer of 2002 when I began lifting weights again. I consumed the above mentioned foods along with Twinlabs’ VegeFuel (a soy isolate protein powder) in my post-workout drink and at other times during the day.

My main reasons for consuming soy were for the protein and for the proposed benefits discussed in this article, especially that soy increases blood antioxidant levels and reduces post-workouts soreness. At this time, I would still get quite sore after my workouts due to continuing effects of my health problems. However, I had previously subscribed to Men's Health magazine . And at the beginning of this year (2003) it began to publish the short blurbs mentioned above about soy lowering testosterone levels. Since I was now getting serious about my weight training and was even thinking of competing again, this was quite a concern as lowered testosterone levels would hamper my training.

Also, I had noticed some years before a significant drop in my sex drive. At the time I had thought this was due to the prescription drugs I was taking the time for a neurological condition. However, I have long since stopped taking such drugs, but my sex drive never increased again. But now I was wondering if there was a connection between the consumption of soy and my lowered sex drive. Also, I began to notice that I felt “weird” after consuming soy foods. It’s hard to explain what this feeling was. It was just a general sense that “something” wasn’t right. So it seemed possible that soy was doing “something” to my body, and this something probably wasn’t good. Also at this time I came across charts like the above that showed soy was not that high of a quality of protein. But since I was now powerlifting, I knew I needed the highest quality proteins possible for recovery from my grueling workouts.

So with these concerns, in the spring of 2003, I stopped consuming soy altogether and began focusing on animal sources for my protein needs. These include lean beef, skinless baked chicken and turkey, fish, low-fat yogurt, and eggs, along with egg and milk proteins based protein powders. In the following months, I noticed a definite increase in my sex drive. Also, my training had been going incredibly well. So I entered a couple of powerlifting contests and broke several IPA records. During that time my health in general also steadily improved. However, it’s hard to say if any or all of this had anything to do with the stoppage of the consumption of soy.

But if I were to consume any soy, I would be sure it was Non-GMO" soy (i.e., soy that has not been genetically modified), such as Jarrow Formula's Iso-Rich Soy. I used to use it as one of my protein powders. I say this as speaker at a health seminar I attended a while ago claimed that any problems associated with soy are only seen with GMO soy, not non-GMO soy. I wasn't able to find any evidence one way or another to confirm this, but still, I would prefer to eat non-GMO foods whenever possible. And since something like 90% of the soy produced in the USA is GMO soy, if a soy product does not specifically say it is "non-GMO" most likely it is GMO soy.

To attain the benefits claimed or soy, I make sure I consume ample quantities of the various above recommended cancer and heart disease preventative foods, like fish, yogurt, fruits and vegetables, nuts and seeds, and whole grains.


So there are many proposed benefits to soy consumption, and there is some evidence supporting all of these benefits. But in most cases, the evidence is not clear-cut. And there are other ways to attain all of the proposed benefits. There are also possible drawbacks to the consumption of soy. Having weighted these pros and cons, I have decided not to consume soy. But only the reader can decide for yourself if soy would be a healthy food for you to consume or if is a food you would be best off to avoid.

October 2014 Update

In October of 2014 I thought of trying to reincorporate soy into my diet. I was thinking of doing so as I've been consuming a lot of dairy, so I figured it might be good to replace one of the 1-2 servings a day of the Natural Whey and Natural Casein Protein Powders I was consuming with a soy protein powder. But before spending the money on a container of soy protein powder, I purchased a much cheaper half gallon of Giant Eagle brand Organic, Plain Soymilk. Being organic, by definition, it is also non-GMO. And this product only contains water, soy, sugar, and natural flavoring, plus several vitamins and minerals. So if I had a problem with it, it would most likely be the soy.

But first, I should mention that a common symptom I experience if I consume something I am allergic to is I am not able to sleep at night. I know that sounds weird, but it has happened so many times that I know it to be true. That said, I drank one cup of this soymilk with my pre-workout cereal about 3pm. That night, I went to bed about 10:15 pm as usual, but then at 2 am I woke up, wide awake. Again that is what happens when I am exposed to allergens during the day. Then after that I tossed and turned the rest of the night. I might have fell asleep for short periods of time, but I was definitely not rested when I got up at 6 am.

But I wanted to be sure it was the soymilk, so the next day I did the same thing. But this time something strange happened. About 9 pm I began feeling very cold while watching TV, even though it was 70 degrees in the room. Then when I went to bed, I put on all of my covers, but I was still cold, even though it was 69 degrees in my bedroom. I was so cold I had a hard time falling asleep. Then throughout the night I repeatedly wake up shivering, stayed awake for a while, then fall back asleep, only to wake up again freezing. Finally at 4 am I felt warmed up, took off a blanket, and fell asleep until my alarm went off at 6 am. I have never experienced such a thing before, but I can only guess that it was related to soy's propensity to mess up hormones.

But whatever the case, that was the end of my thought of using soy again. I was rather obviously allergic to it, and it might have been having other weird effects on my body. But before this little failed experiment, I had taken the time to do a little research on soy protein powders. So I will relate what I learned and was thinking of doing if the soy experiment had gone well, so if the reader wishes to use such products, you will know where to begin.

iHerb is my "go to" source for natural foods and supplements, so the following links are to it. If you order any of these items, use referral code HOP815 to receive $5.00 off your first order. I first checked to see if  Jarrow Formulas, Iso-Rich Soy, Powder was still available, and I was pleased that it was and that it still is non-GMO. It contains natural vanilla flavoring but no sweetener, so I first thought of sweetening it with liquid stevia. But all such products contain either alcohol, which I am also allergic to, or glycerin, which gives me runny stools. But then I noticed Now Foods, Certified Organic, Better Stevia, Extract Powder. It contains only stevia, so it would be a good product to use. And that would give me a relatively good tasting vanilla soy protein.

But then I looked for Twinlab, Vege Fuel, Unflavored, Powder. I had used this product a long time ago before switching to the Jarrow product, as the Jarrow product was non-GMO while the Twinlab wasn't. But I was pleased to see that the Vege Fuel is now also non-GMO. Kudos to Twinlab for making the switch. But the Twinlab product has no flavoring or sweetener. So I figured I use the Now Stevia Powder to sweeten it, and for flavoring, I'd use Now Foods, Healthy Foods, Certified Organic, Cocoa Powder. In that way, I'd have both a vanilla and a chocolate flavored soy protein powder. So if you're going to use a soy protein powder, you might want to give those ideas a try.

Soy: Health Food or Food to Avoid? - References

Soy: Health Food or Food to Avoid? Copyright 2003-2005 by Gary F. Zeolla.

Disclaimers: All company and products names are registered trademarks of the respective companies.

The material presented in this article is intended for educational purposes only. The author is not offering medical or legal advice. Accuracy of information is attempted but not guaranteed. Before undertaking any diet, exercise, or health improvement program, one should consult your doctor. The author is in no way responsible or liable for any bodily harm, physical, mental, or emotional, that results from following any of the advice in this article.

The above article was posted on this site October 7, 2003.
It was last updated September 3, 2005.

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