"Overall, with the exception of those who are allergic, there is little evidence (from the 31,249 research papers published since 1966) that soyfoods are contraindicated for any individual.
In the same way that nutritionists recommend whole grains over refined grains, and apples over apple juice--minimally processed soyfoods should be emphasized over more highly-processed forms of soy.
The soy intake associated with a range of benefits in Asian epidemiologic studies, from reductions in coronary heart disease risk to protection against prostate cancer is about 2 servings of traditional soyfoods per day (about 15-20 grams of protein with 50-75 mg isoflavones), although optimal levels may be somewhat higher."
-Mark Messina, "Insights Gained from 20 Years of Soy Research," Journal of Nutrition 140:2289S-2295S, 2010-
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The Big Question everyone asks me---so what do you think about soy? Up until recently, I just wasn't sure. Not anymore.
Soy is now back on my list of go-to favorite foods. I'm talking whole soy--not fake fatty fractionated processed soy "Buffalo wings" or powdered soy protein--but real food.
Eden's soy mik made with whole soy beans lightens my morning coffee. Grilled NaSoya low-fat firm tofu tops my Vietnamese noodle salad and my amazing soba noodle miso soup. SoyBoy's low-fat tempeh is in my husband's shepherd's pie and in my favorite spicy barbecued-sauced tempeh sandwich.
Here's the goal: Eat your soy just like it's eaten by Asians--not in pill, powder, or fractionated form--but in one or two servings a day of the real thing--soy milk made from soybeans, tofu, tempeh, miso, or edamame.
Here's why soy is back on my list: First, I had a chance to hear Mark Messina, one of the top U.S. soy experts, speak at a conference--and then I followed that up with reading the Journal of Nutrition's December 2010 Soy Summit issue. I'm now convinced that there's every reason to include whole soy as part of a plant-based diet--or any diet. Messina is definitely not a soy salesman--he doesn't oversell soy. If anything, he's conservative and measured. It's not a miracle food--and the evidence for its health benefits ranges from speculative to very encouraging.
Bottom Line: the health benefits of soy are just too good to pass up.
As always, there's way too much to write about in a one post. So here are the essentials--including the real story behind all the internet-inspired hype that has maligned soy's name in recent years.
The Short Story. Add soy....
- For its high quality nutrition & its complete high protein content
- To expand your cooking repertoire--soy is versatile--especially if you're trying to eliminate animal protein
- For its heart health benefits
- For possible prostate cancer protection
- For breast cancer protection if consumed early in life--lower rates of cancer are seen when girls eat 1-2 servings of soy starting at age 5. If you're all grown-up--soy won't hurt--but right now, don't expect it to prevent breast cancer.
- For possible hot flash reductions of around 50%--results have been mixed--but if it works you'll definitely know it in a few weeks. 7 out of 9 recent studies using high-genistein supplements showed significant improvement. Who knows?
- Bone density benefits have been seen in the longer-run whole soy food studies--but the shorter-run U.S. studies that used supplements have been disappointing
- Soy is perfectly safe. There are no studies showing negative effects in humans--None!
- For breast cancer survivors--clinical studies show "a lack of harm" from soy in breast cancer survivors--So go for it! Recent large Asian epidemiologic studies have shown that soy reduced breast cancer deaths & recurrences in Chinese women. Read: "Can Clinicians now assure their breast cancer patients that soyfoods are safe?" Women's Health 2010:6(3):335-338.
Who Is Mark Messina and Why Should I Listen to What He Has to Say?
Mark's a PhD nutritionist who worked for years at the National Cancer Institute, allocating funding for research on the effects of soyfoods on cancer. He's a researcher's researcher--who understands the "strengths & weaknesses of wide variety of experimental models and designs"--and he knows which research is gold-standard stuff--that can give us real answers.
With 31,249 papers on soy written since 1966, Messina is an expert at separating good studies from bad. And he knows full well, with that many articles out there, any "interest group" can cherry pick an article if they want to stir up doubt about soy. But Messina knows soy research better than most--and he can easily explain away the handful of articles that have stirred up doubt about the benefits of soy over the past ten years. Bottom Line: Any harmful effects of soy have only been observed in animals. No harmful effects have been in observed in humans.
Concerned about soy and estrogen, breast cancer, soy formula, femininization of males, thyroid issues, or cognitive impairment? All are either unfounded--except for some very minor--and easy-to-correct concerns about soy and undiagnosed hypothyroid disease.
Full Disclosure: Messina owns a consulting company that has clients who manufacture or sell soyfoods. The Soy Summit which was published in the Journal of Nutrition was organized by Columbia University, but it was funded with a non-restricted grant from Pharmavite LLC. All the soy studies are out there for any of us to read. If you have specific concerns--go to the original research. In the past two years, three major articles on the benefits of soy for breast cancer survivors have been published in prominent medical journals.
The Benefits of Whole Soy Foods
It's a Nutritional Powerhouse - Check It Out!
Whole soy foods bring a lot more to the table than some of the other plant-based competition.
- An excellent source of fiber, resistant starch (the good kind that keeps you slim), certain vitamins & minerals, including the biggies like folate & potassium--and in the U.S. many of us are getting only half of the potassium we need.
- High antioxidant content--the ORAC rank for edamame is equivalent to that of high-ranking strawberries.
- It's a low-glycemic carbohydrate--the good stuff that keeps insulin-resistance at bay--and keeps you full longer.
- Excellent source of protein--much higher than in other beans & legumes. It's a highly digestible protein, and unlike many plant foods, soy has all the essential amino acids. It's protein quality rating is #1, the same as that of dairy & eggs.
- Excellent source of zinc, iron (based on recent research), and it's calcium absorbability is on par with cow's milk.
Show Me What It's Got in the Health Department
- Soy lowers LDL cholesterol. Meta-analyses & reviews from 2004-2007 have shown a 3-5% decrease in LDL cholesterol, on par to that of soluble fiber. When soy protein is substituted for animal protein, the LDL cholesterol levels decrease further, by 8%.
- Large Japanese study (followed 27,435 40-59 year old women for 12.5 years) compared eating 1.5 servings/a day of soy to .5 serving/day of soy--Result: strokes, heart attacks, & cardiovascular disease was reduced by two-thirds in the 1.5 serving group. Japan now recommends 3 servings a day of soy foods.
- Protective benefits seen in the Japanese study aren't from the lowering of cholesterol--the favorable effects were likely from lowering of homocysteine levels, lowering of oxidation levels, and improved endothelial function.
- Improved endothelial function (the flexibility of blood vessel linings) as measured by flow-mediated dilation for those with impaired endothelial function--a recent meta-analysis. Plant estrogens are responsible for the improved endothelial function.
- Both isolated soy protein and soy foods lower blood pressure--but soy foods lower it twice as much as the isolated soy protein does--according to a recent meta-analysis
- Fracture risk was reduced by 33% in post-menopausal Chinese women who ate the most soy foods, compared with those who ate the least. Results from the 4.5 year Shangai Women's Health Study, and the 7.1 year Singapore Chinese Health Study. Note: these are epidemiologic studies.
Clincal trials run in the U.S. have shown no bone benefits--they've been small (less than 50 women), of short duration (mostly 1 year) and they've used isoflavone supplements--not food. But, a 2 year Italian study (150 women) using 54 mg of a genistein supplement (equivalent to 4 servings of soy) showed spinal bone mineral density (BMD) increases of 5.8%--while the placebo group's BMD decreased by 6.4%. Similar effects seen at the hip. Third year of the study showed even greater increases.
Possible reasons for differences between Chinese epidemiologic studies & U.S. clinical trials: Differences in exposure time to soy--Chinese results may reflect a life-long intake of soy--and eating whole soy may be more beneficial than the extracted soy isoflavones used in the U.S. trials.
Further studies on soy and bone unlikely in the U.S. because of lack of benefit that's been shown in clinical trials here--using isoflavone supplements.
Understanding How Soy's Phytoestrogens Are Different from Estrogens
Get this straight--phytoestrogens (plant estrogens) are very different from the estrogens our body makes. In fact, parts of phytoestrogens are anti-estrogenic.
Messina says they should be called SERMS or selective estrogen receptor modulators--the same as tamoxifen or raloxifen--the drugs used to prevent breast cancer and osteoporosis.
Here's why: OK it's kind of technical. Phytoestrogens bind to & activate beta estrogen receptors in the breast--which inhibit the effects of the alpha estrogen receptors, which stimulate breast tissue. The clinical data is very clear. You don't see the stimulation of breast tissue in women who eat soy because of the (SERM) selective estrogen receptor modultator effect of soy phytoestrogens. According to Messina, when it comes to breast tissue, it's soyfood first for breast cancer protection--but in the U.S. we'll unlikely never see clinical studies using soyfoods--or they'll be too short or too small--and they'll likely use isoflavone supplements. If you want to study the effects of soy foods on breast cancer you have to look at the long-term Asian studies.
Breast Cancer Benefits
The bad news for grown-ups: You have to start young. It's likely that eating soy will only prevent breast cancer if it's eaten early in life--from ages 5-18. That's what the Asian epidemiologic evidence has shown. But, Messina likes to base his conclusions on clinical data--and one small study has delivered the goods. 11 grams of soy protein a day--about 1.5 cups of soy milk--consumed from ages 5-11 showed a 50% less likelihood of getting breast cancer. If you're post-menopausal, and you've never eaten soy--it's likely too late to prevent breast cancer--but it definitely won't cause harm.
Messina's bold recommendation: All young girls between ages 5-18 years old should consume one serving of soy a day!
"Generating clinical support for the early soy intake hypothesis is clearly a high-priority research need. Nevertheless, even without these data, because the potential public health benefit is so great and the dietary behavior required for deriving the proposed benefit so minimal and easily achieved, there appears little reason for health professionals not to encourage girls and female adolescents to consume 1 serving/day of soy, the approximate amount associated with protective effects in epidemiologic studies." Mark Messina J Nutr (2010) 140:2289S-2295S
The Breast Cancer Research
- Recent meta-analysis on the effect of soy on breast cancer showed that it works when you consume soy as a real food, start at a young age, and eat at least 1-2 servings a day. A 16% reduction in breast cancer risk is seen for every 10 mg of isoflavones consumed in soy foods--my Eden soy milk has 69 mg of isoflavones per 1 cup. Four additional epidemiologic studies on childhood soy consumption have shown breast cancer risk reductions from 28-60%.
- Three recent landmark studies have shown that for women who already have breast cancer, those who consumed soy foods experienced a decreased risk of death or cancer recurrence, compared to those who did not consume soy. Even among postmenopausal women treated with tamoxifen, there was an approximately 60% reduction in breast cancer recurrence in the highest soy groups--compared to the lowest. Soy further enhanced the recurrence reduction rates in women who were treated with Arimidex or tamoxifen. Click here , here, and here for the articles. All three articles noted that the women consumed typical Asian servings of soy--the highest group consumed >42.3 mg of soy isoflavones--the lowest group consumed <15.2 mg of soy isoflavones. Messina cautions that these studies followed Chinese women--and the results might not translate to the U.S. where soy foods aren't a part of our typical diets.
- In animal studies soy inhibits prostate cancer by 30%.
- Soy lessens the side effects of radiation in prostate cancer treatment
- In a recent meta-analysis (looking at multiple studies), "Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis," the authors conclude that consumption of soy foods is associated with a reduction in prostate cancer risk in men. This protection may be associated with the type and quantity of the soy foods consumed.
- Research suggests that soy isoflavones inhibit prostate tumor spread.
"Because prostate tumors are slow growing and are typically diagnosed late in life, even modestly delaying tumor onset and/or growth can profoundly affect prostate cancer mortality. As was the case for breast cancer, the operating hypothesis is that if soy foods reduce prostate cancer risk, it is because they contain isoflavones."
No Soy Worries
- Soy formula worries: The Arkansas Children’s Nutrition Center has been conducting a prospective, longitudinal study (The Beginnings Study) on breast-fed, milk formula-fed and soy formula-fed children from birth through age six years. After five years, Dr. Thomas Badger, the lead investigator, says the results suggest that soy formula supports normal growth and may have advantages in promoting bone development. To read the study click here. When breast-feeding isn't possible, it looks like soy is OK.
- Soy & Cancer worries: Whole soy doesn't stimulate tumors. It's likely they won't regress--but they won't grow. According to the American Cancer Society's just updated position statement: up to 3 servings a day of traditional soy foods won't be harmful. Soy foods do not adversely affect markers of breast cancer risk, including breast tissue density, breast cell proliferation, and circulating estrogen levels.
- Worries about the feminizing effects of soy on males: The evidence, especially the clinical data, has shown that feminization concerns are unwarranted--whether with soy foods or soy supplements--whether at levels that are equal to or greater than the typical Asian intake. No worries about soy affecting testosterone levels or gynecomastia.
- Thyroid worries & questions: These concerns stem from early in vitro & animal studies--and cases of goiter in the 1960s from soy formula. Lack of iodine was the culprit--and thereafter soy formula was fortified. Soy has no ill effects on healthy thyroids. Soyfoods may slightly increase the amount of thyroid medications needed by people with hypothyroidism, because soy may inhibit the drug's absorption--but this is common with some herbs, drugs, & fiber supplements. It is not necessary for thyroid patients (with the exception of infants with congenital hypothyroidism) to avoid soy foods, because the medication can be taken on an empty stomach and dosages can be easily adjusted to compensate for any effects of soy. Two situations do warrant further study: 1. People with subclinical hypothyroidism, around 5-10% of the U.S. post-menopausal women, and 2. People with iodine deficiency--typically uncommon in the U.S.
- Impaired Cognitive function: Two studies--one in Hawaii & one in Indonesia raised concerns about cognitive impairment & memory problems showing up in elderly men & women who ate a lot of tofu. Interestingly, the tempeh eaters showed improved memories. The likely explanation for the association of cognitive problems to eating tofu is due to both the reporting flaws in one of the studies--and the discovery that formaldehyde was found in the Indonesian tofu. It's sometimes used as a preservative in Indonesian tofu production, and formaldehye is known to adversely affect the memory. My non-medical two-cents: could it be lack of vitamin B-12 in those tofu eaters? After all, tempeh provides B-12. If you're eating plant-based--don't forget your vitamin B-12--it benefits the brain. Click here to read more. Since those 2 studies, "at least 8 different clinical studies evaluating the cognitive effects of soy foods or isoflavones on postmenopausal women" have been conducted. Their data show the potential for cognitive benefits from soy--but it's too soon to draw definitive conclusions.
- Soy allergies: soy is part of the Big Eight of common allergies, like milk, eggs, peanuts, & wheat--but they aren't all equal--soy is at the bottom of the Big Eight list. It's more common in kids, and many outgrow it after age 10.
So there you have it! If you've given up on soy for vague rumors about its safety--give it a second try. 1-2 servings a day is about right. Make sure it's a whole food--and look for the low-fat varieties--they're out there. A cancer nurse advised me to look for soyfoods made with non-GMO soybeans. Just a suggestion.