From thebook, The Metabolic Makeover by Stephen Cherniske and Dr. Natalie Kather. (Altea Media 2013)
In the 80s and 90s, soy was the savior of mankind. It was going to replace meat, prevent cancer and heart disease, and feed a growing world population. Then in 2000, suddenly soy was poison. I was shocked at how far and how rapidly the pendulum swung; to the point where even educated people were scanning the ingredient list of everything they consumed in order to avoid eating a milligram of soy.
I don’t mind the pendulum swinging a little. That’s called self-correction. Common sense tells you that human beings are designed to eat a wide variety of protein sources. Making soy your major protein source could very well cause or contribute to significant health issues.
But the exaggeration and the intentional misrepresentation of research regarding soy was staggering. I’m happy to say that the pendulum is finally heading back to center. Here’s what we believe that looks like:
Asians who eat a lot of soy have a lower incidence of certain cancers, most notably breast cancer and prostate cancer. But is there a causative relationship between consuming soybeans and a lower incidence of cancer or is it merely an association? In other words, I sing in the shower every morning and the sun rises. Does my singing cause the sun to rise, or do these events simply coincide? You get the picture.
Scientists looking for causation found two components of soybeans with anti-cancer activity. The first are phytoestrogens, a group of compounds (e.g., genistein and daidzein) that have estrogen-like activity in humans and animals. Sometimes, these are called isoflavones.
Soy phytoestrogens have very weak activity in humans. But because they bind to estrogen receptors in a woman’s breasts and reproductive organs, it is believed that they block the binding of more powerful estrogens that she may be producing or getting from the environment. Strong estrogens can promote cancer. So there is a good chance that the lower cancer rates in Asian women relate to the blocking effect of phytoestrogens. In men, a similar benefit from soy may be achieved in the reduction of prostate cancer where estrogen plays a contributing role.
Second, scientists found a group of protease inhibitors in soy and other beans. These biochemicals inhibit the digestion of protein by interfering with the activity of two important enzymes, trypsin and chymotrypsin. Protease inhibitors interfere with cell communication, protein metabolism, and cell growth.[ii] This may contribute to anti-cancer defense in humans by interfering with the growth and spread (metastasis) of tumors.
So we now have a reasonable cause and effect hypothesis between two biochemicals (phytoestrogens and protease inhibitors) and reduced cancer. What do we do with this valuable information?
Option one: We promote soy as the perfect food for all human beings, including infants.
Option two: We carefully evaluate the effects of phytoestrogens on pregnancy and fetal health. We evaluate the effects of phytoestrogens and protease inhibitors on the growth of children, and we look for possible side effects resulting from decreased estrogen binding. Estrogen, for example, plays an important role inthe maintenance and repair of the brain.
For decades, many Americans pursued option one with wild abandon. Fueled by the burgeoning soybean industry and supported by thousands of health-food enthusiasts (motto: where’s the next panacea?), the soy frenzy extended to the mass marketing of soy milk, soy protein, soy cheese,soy burgers, soy candy bars, soy butter (to replace peanut butter) andsoy-enriched cereal, bread, pasta, and chips. Concentrates of soy phytoestrogens appeared in health food stores, and the FDA approved the health claim that 25 grams of soy protein per day could reduce risk for heart disease.
Then, new research (the self-correcting power of science) started showing up.
* Excessive soy consumption may inhibit brain repair functions. The basis for this concern arose when researchers documented a dampening effect of phytoestrogens on brain repair in rats.[iii],[iv] Human studies appear to support this finding. A study with Japanese-Americans found a disturbing correlation between soy consumption and cognitive impairment.[v],[vi] I am not suggesting that soy = brain degeneration, but the issue certainly needs further study.
What doesn’t need further study is the association between high soy consumption and growth and development. Here, the concern is that soy phytoestrogens may cause early puberty in girls and delayed physical maturation in boys. It was determined that the amount of phytoestrogens in a day’s worth of soy infant formula had the same estrogenic effect as five birth-control pills to an adult.[vii] A study published in the British medical journal Lancetfound that infants who were fed soy formula had levels of phytoestrogens that were 13,000to 22,000 times higher than natural estrogen concentrations in early life.[viii]
* There is also concern that protease inhibitors found in soy foods may inhibit normal growth and repair functions in children. At first, the soy industry claimed that these inhibitors were destroyed by cooking, but many researchers disagreed. Protease inhibitors have been shown to survive cooking and processing to a small degree, but certainly significant enough for a growing child.[ix]
* The thyroid factor may also create problems for children and adults who consume high amounts of soy foods. The phytoestrogens genistein and daidzein have been found to interfere with thyroid function,[x] and although this has been shown to have no effecton a person eating a varied diet, those using soy as their primary source of protein may suffer.[xi]
The Isoflavone / phytoestrogen controversy
As we write this book, there is no scientific consensus regarding the effect of soy isoflavones on breast-cancer risk, or the benefits for women’s health in general.
When Natalie and I examine the data from conflicting studies— well-conducted scientific investigations that arrive at opposite conclusions—we find a numberof what are calledconfounding variables.
* There is no benchmark population to compare to the Western diet. Intake of isoflavones in North America is estimated to be between 0.5 and 3 mg per day.[xii] Also, there is no “Asian diet.” Evenin the same country (Japan), you find people in the interior eating a lot moresoy than people living on the coast, (who eat more fish) and people in the cities (who eat more meat). Thus daily isoflavone intake varies from 5 to more than 100 mg per day.
*Different soy foods provide different isoflavones. In fermented soy products like natto or tempeh, aglycones are the principal form of isoflavone, whereas in unfermented soy products, like tofu, soy milk or soy supplements, isoflavones are primarily present asglucosides. These different forms are absorbed and metabolized differently.
*At what age did soy food consumption begin, and/or how long should supplements be consumed?
There is evidence that the reduction of breast cancer among Asian women is derived from the consumption of soy foods early in life. Likewise, the observed reduction in breast cancer in women consuming isoflavone supplements occurs mainly in postmenopausal women taking the supplements formore than 5 years.[xiii]
The Bottom Line on Soy:
It’s natural to jump on bandwagons. Nutrition is extremely complex and we would all love a simple solution to the threats of heart disease and cancer. But I’d like to suggest that in regard to soy foods, as in all things, moderation is the key.
• If you eat a lot of meat, you can do yourself and the planet a favor by switching to vegetable proteins at least a few days a week. That’s not just soy foods, but any combination of beans, whole grains, organic dairy foods, nuts and seeds.
• If you are pregnant or nursing, soy should not be your major source of protein. Three to five servings per week appears to be safe, but please consult with your OB/GYN, midwife or pediatrician.
• Natalie and I advise against using soy formula for babies. If you absolutely cannot breastfeed, consult a qualified health professional to work out a rotation strategy using goat’s milk, almond, rice and coconut milk.
• If you have growing children, make sure they have a variety of proteins in their diet. Soy is fine, but if it is their major protein, you may be limiting their adult height.
[ii] Clawson GA. Protease inhibitors and carcinogenesis: a review. CancerInvest. 1996;14(6):597-608.
[iii] Pan Y, Anthony M, Clarkson TB. Effect of estradiol and soyphytoestrogens on choline acetyltransferase and nerve growth factor mRNAs inthe frontal cortex and hippocampus of female rats. Proc Soc Exp Biol Med. 1999Jun;221(2):118-25.
[iv] LephartED, Thompson JM, Setchell KD, Adlercreutz H, Weber KS. Phytoestrogens decreasebrain calcium-binding proteins but do not alter hypothalamic androgenmetabolizing enzymes in adult male rats. Brain Res 2000 Mar 17;859(1):123-31
[v] WhiteLR, Petrovich H, Ross GW, Masaki KH, Association of mid-life consumption oftofu with late life cognitive impairment and dementia: the Honolulu-Asia AgingStudy. Fifth International Conference on Alzheimer’s Disease, #487, 27 July1996, Osaka, Japan.
[vi] 2.White LR, Petrovitch H, Ross GW, Masaki KH, Hardman J, Nelson J, Davis D,Markesbery W, Brain aging and midlife tofu consumption. J Am Coll Nutr 2000Apr;19(2):242-55.
[vii] SoyInfant Formula Could Be Harmful to Infants: Groups Want it Pulled. NutritionWeek, Dec 10, 1999;29(46):1-2.
[viii] Setchell KD, Zimmer-Nechemias L, Cai J, Heubi JE, Exposure of infants tophyto-oestrogens from soy-based infant formula. Lancet 1997 Jul 5;350(9070):23-27.
[ix] Miyagi Y, Shinjo S, Nishida R, Miyagi C, Takamatsu K, Yamamoto T,Yamamoto S. Trypsin inhibitor activity in commercial soybean products in Japan.J Nutr Sci Vitaminol. 1997 Oct;43(5):575-80
[x] DiviRL, Chang HC, Doerge DR, Anti-thyroid isoflavones from soybean: isolation,characterization, and mechanisms of action.Biochem Pharmacol 1997 Nov15;54(10):1087-96.
[xi] Shepard TH. Soybean Goiter. New Eng J Med 1960; 262;1099-1103
[xii] REF: de Kleijn MJ, van der Schouw YT, Wilson PW, Adlercreutz H,Mazur W, Grobbee DE, et al. Intake of dietary phytoestrogens is low inpostmenopausal women in the United States: the Framingham study. J Nutr.2001;131:1826–32.
[xiii]Boucher BA, Cotterchio M, Anderson LN, et al. Use of isoflavonesupplements is associated with reduced postmenopausal breast cancer risk.International Journal of Cancer. 15 March 2013; Volume 132, Issue 6, pages 1439–1450.