Each capsule contains: Novasoy brand Soybean extract (standardized to cotnain 40% isoflavones) 250 mg • LinumLife brand Flax hull concentrate (standardized to contain 3.5% lignans) 220 mg • Alfalfa leaf 8:1 extract 125 mg • Red Clover blossom extract (standardized to contain 8% isoflavonoids) 100 mg. Other Ingredients: Natural Vegetable Capsules, Magnesium Stearate, Microcrystalline Cellulose.
Brand name products often contain multiple ingredients. To read detailed information about each ingredient, click on the link for the individual ingredient shown above.
Below is general information about the effectiveness of the known ingredients contained in the product IsoFlav. Some ingredients may not be listed. This information does NOT represent a recommendation for or a test of this specific product as a whole.
INSUFFICIENT RELIABLE EVIDENCE to RATE
INSUFFICIENT RELIABLE EVIDENCE to RATE
INSUFFICIENT RELIABLE EVIDENCE to RATE
INSUFFICIENT RELIABLE EVIDENCE to RATE
Below is general information about the safety of the known ingredients contained in the product IsoFlav. Some ingredients may not be listed. This information does NOT represent a recommendation for or a test of this specific product as a whole.
POSSIBLY SAFE ...when the leaves are used orally and appropriately, short-term (4,6,12).
LIKELY UNSAFE ...when large amounts are used long-term. Chronic ingestion of alfalfa has been associated with drug-induced lupus effects (381,14828,30602).
PREGNANCY AND LACTATION: POSSIBLY UNSAFE
when used orally in medicinal amounts.
Alfalfa contains constituents with possible estrogenic activity (4,11,30592).
LIKELY SAFE ...when ground flaxseed is used orally and appropriately. Ground flaxseed has been safely used in numerous clinical trials in doses up to 30-60 grams daily for up to 1 year (6803,6808,8020,10952,10978,12908,12910) (16760,16761,16762,16765,16766,18224,21191,21194,21196,21198) (21199,21200,22176,22179,22180,22181,65866,66065) (101943,101949,101950).
POSSIBLY SAFE ...when flaxseed lignan extract or mucilage is used orally and appropriately. Some clinical research shows that a specific flaxseed lignan extract (Flax Essence, Jarrow Formulas) 600 mg daily can be used with apparent safety for up to 12 weeks (16768). Additional clinical research shows that other flaxseed lignin extracts can be used with apparent safety for up to 6 months (21193,21197,21200). In one clinical trial, flaxseed mucilage was used with apparent safety at a dose of up to 5120 mg daily for up to 12 weeks (108047)....when flaxseed is used topically in a warm poultice (101946).
POSSIBLY UNSAFE ...when raw or unripe flaxseed is used orally. Raw flaxseed contains potentially toxic cyanogenic glycosides (linustatin, neolinustatin, and linamarin); however, these glycosides have not been detected after flaxseed is baked (5899). Unripe flaxseeds are also thought to be poisonous when consumed due to cyanide content.
PREGNANCY: POSSIBLY UNSAFE
when used orally.
Flaxseed can have mild estrogenic effects. Theoretically, this might adversely affect pregnancy (9592,12907); however, there is no reliable clinical evidence about the effects of flaxseed on pregnancy outcomes.
LACTATION:
Insufficient reliable information available; avoid using.
LIKELY SAFE ...when used orally in amounts commonly used in foods. Red clover has Generally Recognized As Safe (GRAS) status for use in foods in the US (4912,10372).
POSSIBLY SAFE ...when used orally and appropriately in supplemental amounts. Red clover extracts containing up to 80 mg isoflavones have been used with apparent safety in clinical studies lasting up to 2 years (3375,6127,8925,11089,11091,17091,19540,19556,91524,102901,102840). ...when used topically and appropriately. Red clover extracts have been used topically with apparent safety for up to 4 weeks (102839).
PREGNANCY AND LACTATION: LIKELY SAFE
when used orally in amounts commonly found in foods (4912).
PREGNANCY AND LACTATION: POSSIBLY UNSAFE
when used orally in medicinal amounts.
Red clover has estrogenic activity (19555); avoid using. There is insufficient reliable information available about the safety of the topical use of red clover during pregnancy and lactation.
LIKELY SAFE ...when soy protein is used orally and appropriately. Soy protein products in doses up to 60 grams, providing up to 185 mg isoflavones, daily have been safely used in studies lasting up to 16 weeks (842,2293,2294,2296,3025,3402,3977,4755,6412,8530)(10372,11805).
POSSIBLY SAFE ...when soy extracts are used orally and appropriately, short-term. Soy extracts containing concentrated isoflavones in doses of 35-120 mg daily have been used with apparent safety for up to 6 months (4751,6455,7802,12040,12048,13209,95994,95999).
CHILDREN: LIKELY SAFE
when consumed in amounts commonly found in foods or as a component of infant formula (3400,4912,7331).
Soy milk that's not designed for infants should not be used as a substitute for infant formula. Regular soy milk can lead to nutrient deficiencies (12045). Most evidence shows that exposure to soy formula or other soy products in infancy does not cause early onset of puberty or health or reproductive problems later in life (7331,11080,108245). However, some small cohort studies have suggested that higher soy intake during childhood may be associated with an increased risk of precocious puberty (108240) and may be weakly correlated with the development of breasts in children less than 2 years of age (75520). This is in contrast to an observational study in Chinese children ages 7-9 years which suggests that higher soy intake is associated with delayed puberty (108252). One small cohort study has also found that use of soy infant formula may be associated with an increased risk of endometriosis in adulthood, although endometriosis was also correlated with prematurity, which may have confounded the findings (101803).
CHILDREN: POSSIBLY UNSAFE
when used orally as an alternative to cow's milk in children with severe milk allergy (75359).
Although soy protein-based infant formulas are often promoted for children with milk allergy, children with a severe allergy to cow's milk are also frequently sensitive to soy protein (9883). There is insufficient reliable information available about the safety of soy products when used in amounts higher than typical food quantities for children.
PREGNANCY: LIKELY SAFE
when used orally in amounts commonly found in foods (4912).
PREGNANCY: POSSIBLY UNSAFE
when used orally in medicinal amounts.
Soy contains mildly estrogenic constituents (3373,3988,3989,3990,3994,6029,75303). Theoretically, therapeutic use of soy might adversely affect fetal development; avoid using.
LACTATION: LIKELY SAFE
when used orally in amounts commonly found in foods (4912).
A single 20-gram dose of roasted soybeans, containing 37 mg isoflavones, produces four to six times less isoflavones in breast milk than provided in a soy-based infant formula (2290). There is insufficient reliable information available about the safety of long-term use of therapeutic amounts of soy during lactation.
Below is general information about the interactions of the known ingredients contained in the product IsoFlav. Some ingredients may not be listed. This information does NOT represent a recommendation for or a test of this specific product as a whole.
Theoretically, alfalfa might increase the risk of hypoglycemia when taken with antidiabetes drugs.
 Details
|
Theoretically, alfalfa might interfere with the activity of contraceptive drugs.
Details
|
Theoretically, alfalfa might interfere with hormone therapy.
Details
|
Theoretically, alfalfa might decrease the efficacy of immunosuppressive therapy.
Details
|
Theoretically, concomitant use of alfalfa with photosensitizing drugs might have additive effects.
Details
Animal research suggests that excessive doses of alfalfa may increase photosensitivity, possibly due to its chlorophyll content (106043). It is unclear if this effect would be clinically relevant in humans.
|
Theoretically, alfalfa might reduce the anticoagulant activity of warfarin.
Details
|
Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.
Details
Some potential benefits of flaxseed are thought to be due to its lignan content. Secoisolariciresinol diglucoside (SDG), a major lignan precursor, is found in high concentrations in flaxseed. SDG is converted by bacteria in the colon to the lignans enterolactone and enterodiol (5897,8022,8023,9592). Antibiotics alter the flora of the colon, which could theoretically alter the metabolism of flaxseed.
|
Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.
Details
|
Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.
Details
|
Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.
Details
|
Theoretically, taking flaxseed might decrease the effects of estrogens.
Details
Flaxseed contains lignans with mild estrogenic and possible antiestrogenic effects. The lignans seem to compete with circulating endogenous estrogen and might reduce estrogen binding to estrogen receptors, resulting in an anti-estrogen effect (8868,9593). It is unclear if this effect transfers to exogenously administered estrogens.
|
Although some laboratory research suggests that red clover may have anticoagulant and antiplatelet activity, clinical research has not shown this effect.
Details
In vitro research suggests that genistein in red clover has antiplatelet effects, and historically, red clover was thought to have anticoagulant effects due to its coumarin content. However, some experts state that this is unlikely as most natural coumarins have not been shown to have anticoagulant effects, and their content in red clover is low (17091,19557,19558,19559). Additionally, some clinical research in postmenopausal patients found no effect on coagulation or prothrombin time with the use of red clover flowering tops 378 mg daily for 12 months or red clover isoflavone (Rimostil) 50 mg daily for 2 years (17091,91524).
|
Theoretically, soy might reduce the clearance of caffeine; however, a small clinical study found no effect.
Details
Red clover contains genistein. Taking genistein 1 gram daily for 14 days seems to inhibit caffeine clearance and metabolism in healthy females (23582). However, this effect does not seem to occur with the lower amounts of genistein found in red clover. A clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of caffeine (105693).
|
Theoretically, red clover might increase levels of drugs metabolized by CYP1A2; however, a small clinical study found no effect.
Details
In vitro evidence shows that red clover inhibits CYP1A2 (12479). However, a clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of caffeine, a CYP1A2 probe substrate (105693).
|
Theoretically, red clover might increase the levels and clinical effects of drugs metabolized by CYP2C19.
Details
In vitro evidence suggests that red clover weakly inhibits CYP2C19 (12479). This interaction has not been reported in humans.
|
Theoretically, red clover might increase levels of drugs metabolized by CYP2C9; however, a small clinical study found no effect.
Details
In vitro evidence suggests that red clover might inhibit CYP2C9 (12479). However, a clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of tolbutamide, a CYP2C9 probe substrate (105693).
|
Theoretically, red clover might increase levels of drugs metabolized by CYP3A4; however, a small clinical study found no effect.
Details
In vitro evidence shows that red clover might inhibit CYP3A4 isoenzymes (6450,12479). However, a clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of alprazolam, a CYP3A4 probe substrate (105693).
|
Theoretically, concomitant use of large amounts of red clover might interfere with estrogen therapy.
Details
|
Theoretically, red clover might increase the risk of methotrexate toxicity.
Details
In a case report, a 52-year-old female receiving weekly methotrexate injections for psoriasis developed symptoms of methotrexate toxicity, including severe vomiting and epigastric pain, after three days of taking red clover 430 mg daily. Toxicity resolved after red clover was discontinued. However, no liver function tests or methotrexate levels were reported (91522).
|
Theoretically, the phytoestrogens in red clover might interfere with tamoxifen.
Details
In vitro and animal research suggests that genistein, a constituent of red clover, might antagonize the antitumor effects of tamoxifen (8192). However, there is some evidence from an animal study that red clover does not reduce the efficacy of tamoxifen (102901). Until more is known, tell patients taking tamoxifen to avoid red clover.
|
Theoretically, antibiotics may decrease the activity of soy isoflavones.
Details
Intestinal bacteria are responsible in part for converting soy isoflavones into their active forms. Antibiotics may decrease the amount of intestinal bacteria and decrease its ability to convert isoflavones (7657).
|
Soy can lower blood glucose and have additive effects with antidiabetes drugs.
Details
Clinical research shows that whole soy diets and soy-based meals reduce fasting glucose levels in diabetic and non-diabetic individuals (75268,75296,75378,75493,96001). Also, individuals following a soy-based meal replacement plan seem to require lower doses of sulfonylureas and metformin to manage blood glucose levels when compared with individuals following a diet plan recommended by the American Diabetes Association (75268).
|
Theoretically soy protein may have additive effects with antihypertensive drugs and increase the risk of hypotension.
Details
|
Theoretically, soy might reduce the clearance of caffeine.
Details
Soy contains genistein. Taking genistein 1 gram daily for 14 days seems to inhibit caffeine clearance and metabolism in healthy females (23582). This effect has been attributed to inhibition of the cytochrome P450 1A2 (CYP1A2) enzyme, which is involved in caffeine metabolism. It is unclear if this effect occurs with the lower amounts of genistein found in soy.
|
Soy might modestly induce CYP2C9 enzymes. However, this effect does not seem to be clinically significant.
Details
In vitro research suggests that an unhydrolyzed soy extract might induce CYP2C9. However, the significance of this interaction is likely minimal. In healthy females taking a specific extract of soy (Genistein Soy Complex, Source Naturals), blood levels of losartan, a CYP2C9 substrate, were not significantly affected (16825).
|
Theoretically, soy might have additive effects when used with diuretic drugs.
Details
Animal research suggests that genistein, a soy isoflavone, increases diuresis within 6 hours of subcutaneous administration in rats. The effects seem to be similar to those of furosemide (75604). This effect has not been reported in humans.
|
Theoretically, soy might competitively inhibit the effects of estrogen replacement therapy.
Details
Soy contains phytoestrogens and has been shown to have estrogenic activity in some patients (3860). Although this has not been demonstrated in humans, theoretically, concomitant use of soy with estrogen replacement therapy might reduce the effects of the estrogen replacement therapy.
|
Soy products might reduce the absorption of levothyroxine in some patients.
Details
Preliminary clinical research and a case report suggest that soy-based formulas inhibit the absorption of levothyroxine in infants with congenital hypothyroidism (20636,20637,75548,90959). A levothyroxine dosage increase may be needed for infants with congenital hypothyroidism while using soy-based formulas, and the dose may need to be reduced when soy-based formulas are no longer administered. However, in postmenopausal adults, clinical research shows that taking a single dose of soy extract containing isoflavones 60 mg along with levothyroxine does not affect the oral bioavailability of levothyroxine (95996).
|
Taking soy products containing high amounts of tyramine along with MAOIs can increase the risk of hypertensive crisis.
Details
Fermented soy products such as tofu and soy sauce contain tyramine, a naturally occurring chemical that affects blood pressure regulation. The metabolism of tyramine is decreased by MAOIs. Consuming more than 6 mg of tyramine while taking an MAOI can increase the risk of hypertensive crisis (15649). The amount of tyramine in fermented soy products is usually less than 0.6 mg per serving; however, there can be significant variation depending on the specific product used, storage conditions, and length of storage. Storing one brand of tofu for a week can increase tyramine content from 0.23 mg to 4.8 mg per serving (15649,15701,15702). Advise patients taking MAOIs to avoid fermented soy products that contain high amounts of tyramine.
|
Theoretically, combining soy isoflavones with transdermal progesterone may worsen bone density.
Details
Clinical research suggests that significant bone loss may occur in females with osteoporosis who receive a combination of transdermal progesterone with soy milk containing isoflavones when compared with placebo, soy milk alone, or progesterone alone (69859).
|
Theoretically, estrogenic soy isoflavones might alter the effects of tamoxifen.
Details
Laboratory research suggests that genistein and daidzen, isoflavones from soy, can antagonize the antitumor effects of tamoxifen under some circumstances (7072,14362,8966); however, soy isoflavones might have different effects when used at different doses. A relatively low in vitro concentration of soy isoflavones such as 1 microM/L seems to interfere with tamoxifen, whereas high in vitro concentrations such as those >10 microM/L might actually enhance tamoxifen effects. People on a high-soy diet have soy isoflavones levels ranging from 0.1-6 microM/L. Until more is known, advise patients taking tamoxifen to avoid therapeutic use of soy products.
|
Theoretically, soy might interfere with the effects of warfarin.
Details
Soy milk has been reported to decrease the international normalized ratio (INR) in a patient taking warfarin. The mechanism of this interaction is not known (9672). However, animal and in vitro research suggests that soy may also inhibit platelet aggregation (3992). Dosing adjustments for warfarin may be necessary.
|
Below is general information about the adverse effects of the known ingredients contained in the product IsoFlav. Some ingredients may not be listed. This information does NOT represent a recommendation for or a test of this specific product as a whole.
General
...Orally, alfalfa leaf seems to be well tolerated.
However, a thorough evaluation of safety outcomes has not been conducted.
Most Common Adverse Effects:
Orally: Abdominal discomfort, diarrhea, and flatulence.
Serious Adverse Effects (Rare):
Orally: Lupus-like syndrome after chronic ingestion of alfalfa.
Dermatologic ...Dermatitis associated with alfalfa use has been reported. In a 1954 publication, dermatitis was noted in a 61-year-old female consuming 4-6 cups of tea made with two tablespoonfuls of alfalfa seeds for approximately two months prior to onset. Examination revealed diffuse, confluent edema and erythema on the face, eyelids, ears, hands, forearms, and distal humeral regions. The dermatitis improved with treatment; re-exposure to alfalfa resulted in a similar reaction (30609).
Endocrine
...Alfalfa contains constituents, including coumestrol, with reported estrogenic activity (30586,30592,4753).
Effects in humans are not known.
One case report documents hypokalemia in a female who had been drinking a "cleansing tea" containing alfalfa, licorice, and stinging nettle. The potassium level returned to normal after discontinuing the tea and initiating potassium supplementation. The specific cause of the hypokalemia is not clear. Notably, both stinging nettle and licorice have been associated with hypokalemia and may have been responsible for this effect (30562).
Gastrointestinal ...Orally, flatulence and bulkier feces were reported during the first week of a case series of three subjects ingesting alfalfa (30598). In a case series of 15 patients ingesting alfalfa, increased fecal volume and increased stool frequency was reported. Additional adverse effects included abdominal discomfort in two patients, diarrhea in two patients, loose stools in six patients, and intestinal gas in 13 patients (5816).
Hematologic ...Pancytopenia and splenomegaly were reported in a 59-year-old male who had been taking 80-160 grams of ground alfalfa seeds for up to six weeks at a time, for a five month period. Hematologic values and spleen size returned to normal when alfalfa was discontinued (381).
Other
...Alfalfa products, including sprouts, seeds, and tablets, have been found to be contaminated with Escherichia coli, Salmonella, and Listeria monocytogenes, which have caused documented infections (5600,30566,30568,30572,30569,30564,30604,30610,30563,30607) (30566,30564,30604,30610,30563,30607,30576).
Orally, alfalfa has been associated with the development of a lupus-like syndrome in animals and humans (30594,14828,14830,30602), as well as with possible exacerbations of lupus in patients with known systemic lupus erythematosus (SLE). These reactions may be associated with the amino acid L-canavanine (30594), which appears to be present in alfalfa seeds and sprouts, but not leaves, and therefore should not be present in alfalfa tablets manufactured from the leaves (30601). However, case reports have included individuals ingesting tablets. A lupus-like syndrome was described in four patients taking 12-24 alfalfa tablets per day. Symptoms included arthralgias, myalgias, and rash; positive antinuclear antibodies (ANA) arose anywhere from three weeks to seven months after initiating alfalfa therapy. Upon discontinuation of alfalfa tablets, all four patients became asymptomatic. In two patients, ANA levels normalized (14828). Two additional reports have documented possible exacerbation or induction of SLE associated with alfalfa use. One case involved a female with a 26-year history of SLE, who had been taking 15 tablets of alfalfa daily for nine months prior to an exacerbation. Because of the delay in onset of the exacerbation from the initiation of alfalfa therapy, causation cannot be clearly established (30575). In a different report, SLE and arthritis were found in multiple family members who had been taking a combination of vitamin E and alfalfa tablets for seven years (30602). It is not known what other environmental or genetic factors may have affected these individuals, and the association with alfalfa is unclear.
General
...Orally, flaxseed is usually well-tolerated.
Most Common Adverse Effects:
Orally: Bloating, diarrhea, gastrointestinal complaints.
Serious Adverse Effects (Rare):
Orally: Severe allergic reactions such as and anaphylaxis.
Gastrointestinal
...Integrating flaxseed in the diet can cause digestive symptoms similar to other sources of dietary fiber including bloating, fullness, flatulence, abdominal pain, diarrhea, constipation, dyspepsia, and nausea (12910,16761,16765,21198,21200,22176,22179,65866,101943).
Higher doses are likely to cause more gastrointestinal side effects. Flaxseed can significantly increase the number of bowel movements and the risk for diarrhea (6803,8021,16765). Doses greater than 45 grams per day may not be tolerated for this reason (6802). Metallic aftertaste and bowel habit deterioration have also been reported in a clinical trial (21198).
There is some concern that taking large amounts of flaxseed could result in bowel obstruction due to the bulk forming laxative effects of flaxseed. Bowel obstruction occurred in one patient in a clinical trial (65866). However, this is not likely to occur if flaxseed is consumed with an adequate amount of fluids.
Immunologic ...Occasionally, allergic and anaphylactic reactions have been reported after ingestion of flaxseed (16761). Handling and processing flaxseed products might increase the risk of developing a positive antigen test to flaxseed and hypersensitivity (6809,12911,26471,26482).
Oncologic ...Flaxseed contains alpha-linolenic acid (ALA). High dietary intake of ALA has been associated with increased risk for prostate cancer (1337,2558,7823,7147,12978). However, ALA from plant sources, such as flaxseed, does not seem to increase this risk (12909).
Other ...Orally, partially defatted flaxseed, which is flaxseed with less alpha-linolenic acid, might increase triglyceride levels (6808). Raw or unripe flaxseed contains potentially toxic cyanogenic glycosides (linustatin, neolinustatin, and linamarin). These chemicals can increase blood levels and urinary excretion of thiocyanate in humans. However, these glycosides have not been detected after flaxseed is baked (5899).
General
...Orally and topically, red clover seems to be well tolerated.
Most Common Adverse Effects:
Orally: Myalgia, nausea, and vaginal spotting.
Dermatologic ...Orally, a specific red clover isoflavone product (Promensil) has been associated with mild cases of psoriasis and thrush, although a direct causal link has not been established (9552).
Gastrointestinal ...Orally, red clover has been reported to cause nausea (8194).
Genitourinary ...In human research, 80 mg, but not 40 mg, of a specific red clover isoflavone product (Promensil) increased the duration of menstrual cycles in patients with mastalgia (9552). Red clover has also been reported to cause vaginal spotting (8194).
Hematologic ...In one case report, a 53-year-old female had a spontaneous subarachnoid hemorrhage associated with the use of an herbal supplement containing red clover, dong quai, and eleuthero. It is not clear if this was due to red clover, another ingredient, the combination of ingredients, or other factors (70419). In another case report, a 55-year-old female with protein S deficiency and systemic lupus erythematosus (SLE) had temporary vision loss in the left eye from hemiretinal vein thrombosis 3 days after taking a combination phytoestrogen product containing red clover 250 mg, wild yam 276 mg, dong quai 100 mg, and black cohosh 250 mg (13155). It is unclear if red clover contributed to this event.
Musculoskeletal ...Orally, red clover has been reported to cause myalgia (8194).
Neurologic/CNS ...Orally, a specific red clover isoflavone product (Medoflavon) has been associated with headache, although with a similar frequency to placebo (19545).
Oncologic ...Due to potential estrogenic effects of red clover isoflavones, there has been some concern that red clover might increase the risk of estrogen-sensitive cancers such as breast cancer or uterine cancer. A meta-analysis of 8 clinical trials suggests that increased intake of red clover- and soy-derived isoflavones may modestly increase mammographic breast density in premenopausal, but not postmenopausal, adults when compared with placebo. However, in a sub-group analysis assessing only isolated red clover isoflavones, there was no change in breast density (70428). Furthermore, a 2015 review by the European Food Safety Authority (EFSA) reported no increase in risk of breast cancer in females taking isoflavone-containing supplements (91725). Similarly, no effect was found on endometrial thickness and histopathological changes in the uterus after up to 36 months of supplementation with 40-120 mg daily of isoflavones from red clover extract (91725).
General
...Orally, soy is well tolerated.
Most Common Adverse Effects:
Orally: Bloating, constipation, diarrhea, and nausea.
All ROAs: Allergic reactions.
Endocrine
...In the 1950s and 1960s, cases of altered thyroid function, particularly goiter, were reported in children taking soy formula.
However, adding iodine to soy formula or replacing soy flour in formula with soy protein isolate has nearly eliminated the risk of altered thyroid function in most infants (75353,75651).
In adults, there is some evidence that soy intake can alter thyroid function. Results from one clinical trial suggests that consuming soybeans 30 grams daily for as little as one month can increase thyroid-stimulating hormone (TSH) and decrease thyroxine, causing diffuse goiters, constipation, fatigue, and lethargy in some Japanese men. Recovery was achieved by discontinuing soybean intake (75206,75353). There is also some evidence that soy inhibits thyroid hormone synthesis resulting in increased secretion of TSH in some postmenopausal patients (7806). However, this seems to only occur in people with iodine deficiency (6466,75311). In postmenopausal patients with normal levels of iodine, taking a soy extract for 6 months does not seem to significantly affect thyroid hormone levels (13010).
Evidence from a single case-control study suggests that consumption of soy-based formulas may be associated with an observed three-fold increase in the risk of breast development in Puerto Rican children less than 2 years-old (75520). The correlation has been attributed to the estrogenic activity of soy. However, other risk factors, including a maternal history of ovarian cysts and consumption of meat products were also associated with the increased risk of breast development prior to 2 years of age. Also, the investigators noted that in over half of the cases, the child had not been exposed to soy or any of the other risk factors. Therefore, factors other than soy consumption may be more strongly associated with the increased risk of breast development prior to 2 years of age.
Gastrointestinal ...Gastrointestinal upset, such as constipation, diarrhea, bloating, and nausea are the most common side effects of soy (2297,11033,11082,15851,75491,95999). Reports of "bad taste" and taste intolerance have also been documented in clinical research (15851,39007,75491). Firmer stools, diarrhea, colitis, and intestinal mucosal damage has been reported in infants fed soy protein formula (75161,75448,75516,75525).
Genitourinary
...Orally, soy might increase discomfort during menstrual periods.
Evidence from a small, retrospective cohort study has found that consuming soy formula as an infant may slightly increase the duration and discomfort of menstrual periods later in life. However, the investigators noted that these differences may not be clinically significant (7331).
Orally, frequent soy consumption might be a risk factor for uterine leiomyoma, an estrogen-dependent benign tumor located on the uterus. Observational research found that consumption of soy milk or soybean at least four times weekly is associated with a 7-fold increased odds of uterine leiomyoma (98869).
There is some concern that use of soy-based formulas in infants might result in long-term health complications. However, results from a retrospective cohort study has found that intake of soy-based formula as an infant does not affect height, weight, body mass index, pubertal maturation, menstrual history, or pregnancy history, nor does it increase the risk of reproductive organ disorders, hormonal disorders, libido dysfunction, or birth defects in the offspring of adults who received soy formula as infants (7331,11080). Additionally, research in adults shows that urinary phytoestrogens are not associated with endometriosis risk (101804). However, some population research has found that regular exposure to soy-based formulas during infancy is associated with an increased risk for endometriosis (101803).
Immunologic
...Orally, soy can cause allergic reactions such as skin rash and itching in some people (6412).
In an 11-year-old female, allergy to soy protein resulting in a delayed itching papular rash was thought to be responsible for the reaction to injected benzathine benzylpenicillin containing possible soy protein-contaminated soy lecithin (96422).
Topically, soy-based ingredients were responsible for the development of hand atopic dermatitis in a young female using cosmetic lotions in the workplace. Percutaneous sensitization resulted in the development of anaphylaxis to oral soy (96000).
Neurologic/CNS ...Orally, one clinical study showed that insomnia was more common in postmenopausal adults taking soy isoflavone supplements when compared with those receiving placebo (9917). Some research suggests that dietary consumption of tofu during midlife might decrease cognitive function in later years. Evidence from one retrospective cohort study suggests that males who consume at least two servings of tofu weekly during midlife have increased risk of cognitive impairment in late life (19% vs. 4%) compared to those who consume tofu less frequently. Although the effect of tofu was considered to be marginal compared to other factors such as age, education, or history of stroke, results from the study suggest that the effect of significant midlife consumption of tofu is comparable to the effect of an age difference of 4 years or an education difference of 3 years. However, numerous other factors, such as lifestyle and health, could be involved (6415,6416). Therefore, these findings are too preliminary to be used as a basis for clinical recommendations.
Oncologic
...There is controversy about the role of soy in breast cancer.
Population studies suggest that soy is protective against breast cancer. Asian females who eat a traditional diet high in soy seem to have a lower risk of developing breast cancer (4590,5939,9674). Early exploratory studies have suggested that soy stimulates proliferation of normal human breast tissue (3980,3981). However, taking a soy tablet containing 50 mg soy isoflavones daily for 12 months does not alter mammographic or breast MRI tissue density in adults at high risk of breast cancer, with non-endocrine treated breast cancer, or previously treated for breast cancer and without evidence of recurrence (95999).
There is some concern that soy supplements, but not soy foods, might increase the risk of endometrial hyperplasia due to its estrogenic effects. Population and clinical research suggests that soy foods do not have a proliferative effect on endometrial cells (7358,2429,7654,9676,9917), and increased dietary soy and phytoestrogens are associated with reduced endometrial cancer risk (7338,10372). However, the effects seem to be different with concentrated soy isoflavone extract. While taking products providing isoflavones 120 mg daily for 6 months does not increase endometrial thickening (13209), taking higher doses such as isoflavones 150 mg daily for 5 years might increase the risk of simple endometrial hyperplasia (12105). However, there is no evidence that soy isoflavones increase the risk of atypical hyperplasia which has a much higher risk of developing into endometrial cancer than simple endometrial hyperplasia (12105,90973).
There is also concern that increased soy intake increases the risk for other types of cancer. Some observational research has found that higher dietary intake of soy is associated with a higher risk for bladder cancer and pancreatic cancer (9677,105609).
A meta-analysis of results from cohort and case-control studies evaluating the risk of stomach cancer related to consumption of fermented soy products is unclear and inconclusive. The highest quality data from cohort studies suggests that these products have no significant effect on stomach cancer (7340,7341). More research is required to determine if soy products have any correlation with stomach cancer.
Pulmonary/Respiratory ...Inhaled soy dust and soy hull aeroallergen can trigger symptoms of asthma and allergic rhinitis (5084,5085,5086).
