Hi Mary,
Unfortunately, there is a great deal of misinformation surrounding soy and human health. As with many foods and research, much of this gets dramatized in the media with study headlines, etc.
To answer your question, I have provided some information on soy and thyroid below. We also have scientifically supported and referenced information on our Soy Nutrition website. This site is geared more toward the health care professional, in hopes of dispelling many of these myths and providing sound scientific information. (You can access it at www.soynutrition.com. )
Please let me know if you have any further questions -- and thanks for reaching out to me!
Kind regards,
Elizabeth
Elizabeth Tilak, MS, RD
Nutrition Research Manager
Dean Foods / WhiteWave Foods Company
12002 Airport Way
Broomfield, CO 80027
303.635.4742 (office)
A review of clinical data provides no evidence that soy foods or isoflavones adversely affect thyroid function.
The idea that soy and isoflavones exert anti-thyroid effects is based primarily on several cases of goiter found in infants ingesting soy formula in the early 1960s and more recent research in rodents.(1,2) Due to those early cases of goiter, iodine was added to soy infant formula and the formulation of these products was changed in the mid-1960s, replacing soy flour with isolated soy protein. Since that time, no cases of goiter have been reported among the millions of infants using soy formula.(3,4) Even in the rat, an animal sensitive to anti-thyroid effects,(5) normal thyroid function is maintained in response to the consumption of isoflavones.(1)
A recent review of 14 clinical trials found that with only one exception (a study published in Japanese that was poorly designed(6)), either no effects or only modest changes in healthy thyroid function were noted.(7) In the only trial that specifically examined isoflavone (90 mg/d) supplements in postmenopausal women, no changes were seen in levels of serum thyroid-stimulating hormone over a 6-month period.(8)
Some evidence indicates that soy foods may reduce absorption of medication in hypothyroid patients.(9-12) Such an effect is common with many food-drug interactions - herbs, medications and even fiber supplements - for example.(13-21) In any event, hypothyroid adults can still enjoy the heart healthy benefits of soy foods by working with their doctor to adjust their dosage if necessary.
1. Chang HC, Churchwell MI, Delclos KB, Newbold RR, Doerge DR. Mass spectrometric determination of Genistein tissue distribution in diet-exposed Sprague-Dawley rats. J Nutr 2000;130:1963-1970.
2. Badger TM, Ronis MJ, Hakkak R, Rowlands JC, Korourian S. The health consequences of early soy consumption. J Nutr 2002;132:559S-565S.
3. Merritt RJ, Jenks BH. Safety of soy-based infant formulas containing isoflavones: the clinical evidence. J Nutr 2004;134:1220S-1224S.
4. Poirier LA, Doerge DR, Gaylor DW, Miller MA, Lorentzen RJ, Casciano DA, Kadlubar FF, Schwetz BA. An FDA review of sulfamethazine toxicity. Regul Toxicol Pharmacol 1999;30:217-222.
5. Ishizuki Y, Hirooka Y, Murata Y, Togashi K. The effects on the thyroid gland of soy beans administered experimentally to healthy subjects (In Japanese). Nippon Nailbunpu Kashi (Folia Endocrinol) 1991;67:622-629.
6. Messina M, Redmond G. Effects of soy protein and soy bean isoflavones on thyroid function in healthy adults and hypothyroid patients: A review of the relevant literature. Thyroid (accepted).
7. Bruce B, Messina M, Spiller GA. Isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women. J Med Food 2003;6:309-316.
8. Doerge DR, Sheehan DM. Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect 2002;110 Suppl 3:349-353.
9. Fitzpatrick M. Soy formulas and the effects of isoflavones on the thyroid. N Z Med J 2000;113:24-26.
10. Bell DS, Ovalle F. Use of soy protein supplement and resultant need for increased dose of levothyroxine. Endocr Pract 2001;7:193-194.
11. Conrad SC, Chiu H, Silverman BL. Soy formula complicates management of congenital hypothyroidism. Arch Dis Child 2004;89:37-40.
12. Liel Y, Harman-Boehm I, Shany S. Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients. J Clin Endocrinol Metab 1996;81:857-859.
13. Chiu AC, Sherman SI. Effects of pharmacological fiber supplements on levothyroxine absorption. Thyroid 1998;8:667-671.
14. Shakir KM, Chute JP, Aprill BS, Lazarus AA. Ferrous sulfate-induced increase in requirement for thyroxine in a patient with primary hypothyroidism. South Med J 1997;90:637-639.
15. Liel Y, Sperber AD, Shany S. Nonspecific intestinal adsorption of levothyroxine by aluminum hydroxide. Am J Med 1994;97:363-365.
16. Sperber AD, Liel Y. Evidence for interference with the intestinal absorption of levothyroxine sodium by aluminum hydroxide. Arch Intern Med 1992;152:183-184.
17. Sherman SI, Tielens ET, Ladenson PW. Sucralfate causes malabsorption of L-thyroxine. Am J Med 1994;96:531-535.
18. Siraj ES, Gupta MK, Reddy SS. Raloxifene causing malabsorption of levothyroxine. Arch Intern Med 2003;163:1367-1370.
19. Rosenberg R. Malabsorption of thyroid hormone with cholestyramine administration. Conn Med 1994;58:109.
20. Harmon SM, Seifert CF. Levothyroxine-cholestyramine interaction reemphasized. Ann Intern Med 1991;115:658-659.
21. Zhang X, Shu XO, Gao YT, Yang G, Li Q, Li H, Jin F, Zheng W. Soy food consumption is associated with lower risk of coronary heart disease in Chinese women. J Nutr 2003;133:2874-2878.
"Mary Bell"
07/19/2010 01:31 PM
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Subject Question about soy
Elizabeth,
I am a dietitian in the Dallas area and I had a post show up on a Facebook page that I wanted to follow up on before I responded.
I had commented that dry roasted edamame was a great snack alternative and a good source of soy. One of the comments was the following:
"Soy is actually a problem for anyone with thyroid disorder or disease in their family or in themselves. The isoflavonaoids (soy hormones) interfere with the thyroid hormones in the human body. if one is predisposed due to family history it can bring on the thyroid imbalance. If one is suffering currently with the disorder or disease it can increase the severity of the problems associated with it. I would be careful with soy no matter who you are."
Can you provide any information that would support this person's comments, or at least explain where the concern comes from, as well as provide any information that explains the benefitis of soy in the diet vs. any dangers or concerns?
I am a huge advocate of looking at all sides of an issue before coming to any one conclusion, and I try to impress that upon my readers as well. Your help would be appreciated.
Sincerely,
Mary Bell RD/LD
Owner, Rudog Nutrition
www.rudog.com
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