Nutritional Medicine , Separating Fact from Fiction
The Role of Soy in the Diet of Patients with Hypothyroidism and in Pregnant Women Who are Genetically Susceptible to Thyroid Disorders. Does it deserve another look?
Most of us have heard of all the wonderful benefits of soy protein . . . but, is soy all it’s cracked up to be? Many experts think not. Soy is being promoted as a healthy alternative to estrogen replacement, it is being used in a multitude of foods as a meat replacement, and it is in our infant formulas. Yet, little has been heard on the potential negative effects that soy might have on individuals predisposed to thyroid disease, or on the potential long-term consequences of feeding a soy formula to a baby.
Soy is listed in the drug-nutrient interaction handbook by Pronsky, et al, 2015 indicating that this protein may cause an interference in the absorption of thyroid medication and cautions if soy is to be consumed that it be consumed 4 hours after taking the thyroid medication. Other nutrients/supplements must be taken 4 hours after thyroid medication to assure optimal absorption. These nutrients are:
Goitrogenic substances have a negative impact on thyroid gland functions. Goitrogens are found in the following foods in high concentrations, among others:
In 2014 soy was implicated in playing a role in endometrial cancer in Japanese women (Wan, et al,, 2014). Conclusions drawn stressed the importance of taking population based variables into account when preparing study designs to avoid future controversy and confusion over this relatively ignored variable. The results in this study showed Japanese women at higher risk for endometrial cancer with soy use than other comparable studies utilizing other population subjects.
. The phytoestrogens in soy interfere with iodine metabolism and inhibit thyroid hormone synthesis by blocking the formation of T4, the precursor to the active thyroid hormone called T3. Patients on Synthroid or other thyroid preparations should be cautioned to avoid or limit high Goitrogenic food, abide by the drug-nutrient interaction instructions and avoid too much fiber within 4 hours of taking medication for optimal functioning of the medication provided to support the thyroid gland.
According to Dr. Mike Fitzpatrick, an environmental scientist and phytoestrogen researcher, states that soy products can have a detrimental affect on both adults and infants. In particular, he believes that soy formula manufacturers should remove the isoflavones from the infant formula.
(The part of the soy that acts as an anti-thyroid agent) from their infant formula products).
It has been known since the late 1950’s that soy formulas contain anti-thyroid agents. Infants on soy formula appear to be at greater risk for developing auto-immune thyroid disorder later in life. The formula manufacturers thought they could get around this little problem by adding extra iodine and methionine to their infant formula recipe. This, however, only solved the problem in the short-term to normalize thyroid function in otherwise normal infants. Infants that are already hypothyroid at birth and are on thyroid medication generally have to have their medications increased when they are switched to a soy based formula.
Other studies have replicated results showing many babies fed soy-based formula developed the auto-immune thyroid disorder in later life (Fort P, et al, 1990). In fact, this study found that the frequency of feedings with soy-based milk formulas in early life was noticeably higher in children with autoimmune thyroid disease, and thyroid problems were almost triple in those soy formula-fed children compared to their siblings and healthy unrelated children.
Not much is being done here to educate parents about the potential dangers of soy formula, or to alert the general public that heavy soy consumption may be a danger to thyroid function. Other countries however are far ahead of the U.S. In July of 1996, the British Department of Health issued a warning that the phytoestrogens found in soy-based infant formulas could adversely affect infant health. They advised that breastfeeding be the primary method of feeding babies and if allergies to milk-based formulas were evident, then alternatives to soy-based formulas should be offered.
There is not enough education on how to take thyroid medication so it can be absorbed effectively and thus aide the failing thyroid gland. Such things as taking medication on an empty stomach 20 minutes before food and 4 hours before any iron, magnesium or calcium supplements should be reviewed with the patient. Avoiding foods that inhibit absorption can help the thyroid function optimally, such as avoiding excess fiber close to medication time or consuming goitrogens.
How much soy is safe? For infants, possibly none. This is a controversial area and more research is needed. For adults, just 30mg of soy isoflavones per day is the amount found to have a negative impact on thyroid function. That would approximate 5-8 oz of soy milk, or 1.5 oz. of miso.
For infants born compromised already in thyroid function, or put at potential for development of such, may be the most likely to suffer from the autoimmune form of hypothyroidism if they develop it later in life. With that type of hypothyroidism the medication for the boosting of T4, or thyroxin, is given, but the individual is still fatigued, maybe the hair is falling out, essentially suffering symptoms of hypothyroidism but her TSH and free T4 values are normal. In cases like this the patient will either have to be put on animal glandular tissue replacement or try to correct the problem with the provision of enough, but not too much, selenium to promote conversion of the inactive T4 into the active form of the hormone, T3.
Another recent study showed higher cancer rates in Japanese on the same amount of soy as opposed to Americans. So, we have population variables that have rarely been accounted for in many of these studies making evidence-based findings difficult, contradictory and confusing.
The bottom line again is we are all individuals. Some tolerate soy proteins just fine. Others cannot have it in their diet without problems. Once again, it takes a trained clinician to evaluate all factors in making a determination whether soy is something to be avoided in your personal meal plan or not.
Further research on an evidence-based Thyroid Diet for adults is indicated on a practical level. Suggested future studies involving effects of soy based infant formula on future development of auto-immune thyroid disease in exposed infants with a family history of hypothyroidism is warranted. These studies should include our recent advances in the study of the human microbiome.
Copywrite: Nutritional Synergy, Kathy J. Shattler, M.S., RDN
References and Bibliography
Devi RL, Chang HC, Doerge DR. Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanism of action. Biochem Pharmacol. 1997. 54(10):1087-96
Filisetti TM, Lajolo FM. Effect of the ingestion of soybean fractions, raw or autoclaved on the rat thyroid. Arch Latinoam Nutr.1981.31 (2); 287-302.
Fitzpatrick, M. Soy isoflavones. . Panacea or poison? Available at:www.westonaprice.org/isoflavones. htm
Forsyth WA. Soy protein, thyroid regulation and cholesterol metabolism. J. Nutr. 1995.125 (Suppl3):619S-623S.
Fort P, Moses N, Fasano M, Goldberg T, Lipshitz F. Breast and soy-formula feedings in early infancy and the prevalence of autoimmune thyroid disease in children. J Am Coll Nutr.1990; 9(2):164-7.
Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism; the influence of soy-based formula. J Am Coll Nutr. 1997. 16(3):280-2.
Kawicka and B Regulska-llow.Metabolic disorders and nutritional status in autoimmune thyroid disease. 2015.;69-80. Assessed 4/15/2016.
Klein M, Schadereit R, kuchenmeister U. Energy metabolism and thyroid hormone levels of growing rat in response to different dietary proteins – soy protein or casein. Arch Tierernahr 2000. 53(2);99-125.
Soy on-line. Phytoestrogens and the thyroid. Available at: http://soyonlineservice.co.nz/thyroid.htm.
Soni M, White LR,et al. Phytoestrogen consumption and risk for cognitive decline and demention; With consideration thyroid status and other possible mediators. The J of Steroid Biochemistry and Molecular Biology.2015. Accessed 4/15/16.
Wan Y and E Crosbie. Soy intake and endometrial cancer risk varies according to study population. BLOG. An International Journal of Obstetrics and Gynecology. 2014. 122:311: doi: 10.1111/1471-0528.12859. Accessed 4/15/16.