Soy: benefits, dosage, contraindications
Scientific name(s)
Glycine max
Family or group:
Plants
Active ingredients:
Isoflavones
Calcium
Iron
Potassium
Indications
Scoring methodology
EFSA approval.
Menopause ✪✪✪✪✪
Soy isoflavones are considered for reducing menopausal symptoms, notably hot flashes. Meta-analyses and clinical studies indicate that consumption of soy protein providing 34 to 100 mg of isoflavones per day moderately reduces the frequency and severity of hot flashes, particularly in women who initially experience frequent hot flashes. Controlled trials suggest that concentrated extracts of soy isoflavones, at doses of 35 to 200 mg per day, are comparable to conventional estrogen for reducing menopausal symptoms. One study showed that a genistein extract at 54 mg per day reduced hot flashes by 22% to 29%, compared with 54% with 1 mg of daily estradiol. Recent research indicates that regular soy consumption may also improve other menopausal symptoms such as vaginal dryness and skin hydration. However, effects on breast density and cancer risk remain inconclusive, and soy's effectiveness may vary depending on an individual's ability to convert daidzein into equol, a metabolite with significant estrogenic activity.
Posologie
Oral
34 - 100 mg
Standardized isoflavone extract
Impact of a soy drink on climacteric symptoms: an open-label, crossover, randomized clinical trial
Effect of Isoflavones on Blood Lipid Alterations in Postmenopausal Females: A Systematic Review and Meta-Analysis of Randomized Trials
Soy isoflavones versus placebo in the treatment of climacteric vasomotor symptoms: systematic review and meta-analysis
The effect of dietary soy supplementation compared to estrogen and placebo on menopausal symptoms: a randomized controlled trial
Impact of a soy drink on climacteric symptoms: an open-label, crossover, randomized clinical trial
Use of Plant-Based Therapies and Menopausal Symptoms: A Systematic Review and Meta-analysis
Soy Protein Containing Isoflavones Improves Facial Signs of Photoaging and Skin Hydration in Postmenopausal Women: Results of a Prospective Randomized Double-Blind Controlled Trial
Soy fiber improves weight loss and lipid profile in overweight and obese adults: a randomized controlled trial
Effects of genistein on hot flushes in early postmenopausal women: a randomized, double-blind EPT- and placebo-controlled study
Breast cancer ✪✪✪✪✪
Studies show that high soy consumption may be beneficial for the prevention of breast cancer and its recurrence in some patients. A meta-analysis found that those who consumed more than 15 mg of soy isoflavones per day accounted for about 25% of all breast cancer cases, compared with 75% among those consuming less than 15 mg per day. This effect varies across groups, with Asian and Asian-American women experiencing a significantly reduced risk. In Western populations, even among those who consume the most soy, no preventive effect has been observed, possibly due to genetic differences or methods of quantifying soy intake. However, specific clinical studies on the use of soy isoflavone extracts (200 mg/day for 2 weeks before surgery or 50 mg/day for 12 months) did not show a significant effect on cancer cell growth or breast density.
Posologie
Oral administration
15 - 50 mg
standardized isoflavone extract
A pilot clinical study of short-term isoflavone supplements in breast cancer patients
Double-Blind Randomized 12-Month Soy Intervention Had No Effects on Breast MRI Fibroglandular Tissue Density or Mammographic Density
Phytoestrogen intake and breast cancer risk in South Asian women in England: findings from a population-based case-control study
Soy Isoflavones and Breast Cancer Risk: A Meta-analysis
Tofu and risk of breast cancer in Asian-Americans
Osteoporosis ✪✪✪✪✪
Clinical research indicates that soy protein or extract containing 75–90 mg of isoflavones can increase bone mineral density or slow its loss, and improve biochemical markers of bone turnover in peri- and postmenopausal adults compared with control.nnHowever, lower doses appear less beneficial. Observational studies in postmenopausal Japanese and Chinese women suggest that about 50 mg of soy isoflavones per day is associated with higher bone mineral density. Nevertheless, some conflicting results exist. It may be that only people able to convert daidzein, a soy isoflavone, into S-equol (a metabolite) can derive benefits from soy.nn
Posologie
Oral administration
75 - 90 mg
Standardized isoflavone extract
Systematic review of soy isoflavone supplements on osteoporosis in women
Effect of soy isolate protein and resistance exercises on muscle performance and bone health of osteopenic/osteoporotic postmenopausal women
Equol and Resveratrol Improve Bone Turnover Biomarkers in Postmenopausal Women: A Clinical Trial
Soy isoflavones have a favorable effect on bone loss in Chinese postmenopausal women with lower bone mass: a double-blind, randomized, controlled trial
Short-term effects of high soy supplementation on sex hormones, bone markers, and lipid parameters in young female adults
Muscle strength ✪✪✪✪✪
Soy protein, combined with resistance training, appears to increase muscle strength compared with a placebo. A meta-analysis of three clinical studies shows that consuming soy protein improves strength and lean muscle mass in untrained athletes. Other clinical research also indicates improvements in postmenopausal women. nnA study of Olympic endurance athletes shows that consuming soy protein at 1.5 g/kg daily for 8 weeks increases body mass and strength indices, and reduces fatigue. Soy protein, at 25 g daily in skim milk for 16 weeks, also significantly increases the maximum weight lifted in press and leg-extension exercises in postmenopausal women.nnCompared with other protein supplements such as whey, beef, and dairy products, soy protein appears equally effective at improving muscle strength, although the validity of these results remains limited by the quality of the studies.
Posologie
Oral
25 g
soy protein
Adding Soy Protein to Milk Enhances the Effect of Resistance Training on Muscle Strength in Postmenopausal Women
No Significant Differences in Muscle Growth and Strength Development When Consuming Soy and Whey Protein Supplements Matched for Leucine Following a 12 Week Resistance Training Program in Men and Women: A Randomized Trial
Lactose intolerance ✪✪✪✪✪
Soy milk is an effective alternative to cow's milk for people with lactose intolerance. It can be used in infant formulas to prevent symptoms of lactose intolerance. In particular, formulas based on isolated soy protein are an acceptable option for at-risk infants.
Posologie
Oral administration
soy milk
Metabolic syndrome ✪✪✪✪✪
A meta-analysis of diabetic patients or those suffering from metabolic syndrome shows that adopting a diet high in soy proteins can reduce fasting plasma glucose levels, insulin, and insulin resistance compared with a control diet. Other clinical studies indicate that a diet based on soy protein decreases fasting plasma glucose and LDL cholesterol in postmenopausal women.
Posologie
Oral administration
120 mg
standardized isoflavone extract
Dyslipidemia ✪✪✪✪✪
The use of soy proteins, as a replacement for other dietary proteins, appears to modestly reduce total cholesterol and LDL cholesterol by about 3% to 4% compared with a control group. nnIn the US, for soy products to be eligible for the cholesterol-related claim, they must provide at least 6.25 g of soy protein per serving. However, results vary: some studies show greater effectiveness in patients with more severe hyperlipidemia, while others observe no significant benefit on LDL or triglyceride levels compared with control. nnThe doses of soy protein used in the studies range from 25 to 135 g per day, providing 40 to 318 mg of isoflavones daily, with no evidence that higher doses are more effective.nn
Posologie
Orally
25 - 30 g
soy protein
A Meta-Analysis of 46 Studies Identified by the FDA Demonstrates that Soy Protein Decreases Circulating LDL and Total Cholesterol Concentrations in Adults
Type 2 diabetes ✪✪✪✪✪
Soy-rich diets appear to reduce the risk of type 2 diabetes, and soy protein, unlike isoflavones, modestly improves glycemic indices. A meta-analysis of observational studies found that high consumption of tofu, soy protein, or soy isoflavones is associated with an 8% to 16% reduction in the risk of developing diabetes compared with low consumption. Additional research shows that soy may modestly improve lipid profiles in people with diabetes, slightly reducing total and LDL cholesterol levels over periods of 6 to 12 weeks, without affecting HDL cholesterol or triglyceride levels. Furthermore, regular soy consumption may reduce the risk of cardiovascular disease–related mortality in patients with diabetes, with research suggesting that consuming soy at least four days per week is associated with a 23% reduction in the risk of cardiovascular mortality.
Posologie
Oral administration
40 - 161 mg
standardized isoflavone extract
Dietary Soy Consumption and Cardiovascular Mortality among Chinese People with Type 2 Diabetes
Legume and soy intake and risk of type 2 diabetes: a systematic review and meta-analysis of prospective cohort studies
The association between soy intake and risk of gestational diabetes mellitus: a prospective cohort study
High blood pressure ✪✪✪✪✪
Several meta-analyses have shown that consumption of soy-based products slightly reduces systolic and diastolic blood pressure in patients with prehypertension or mild hypertension. The formulations studied contain 18 to 40 g of soy protein, providing 118 to 143 mg of isoflavones, or 4.5 g of soy peptide per day for 8 weeks. However, these results should be interpreted with caution due to a high risk of bias and the absence of a dose-response relationship. nnIn normotensive patients, consumption of soy protein does not appear to lower blood pressure.nn
Posologie
Orally
118 - 143 mg
isoflavone-standardized extract
Properties
Hormone metabolism
Soy isoflavones, notably genistein and daidzein, are phytoestrogens structurally similar to endogenous estrogens and act as selective estrogen receptor modulators. These components can weakly bind to estrogen receptor alpha and beta, although genistein exhibits a binding affinity comparable to that of 17β-estradiol. This interaction partly explains soy's protective effects against cardiovascular disease, certain cancers, and menopausal symptoms. Isoflavones exert complex, tissue-specific actions, sometimes acting as partial estrogen agonists and antagonists. They also affect plasma membranes and cell signaling pathways in nonclassical ways. Interestingly, isoflavones have a greater affinity for the estrogen receptor beta, which is present in the brain, bones, and vascular epithelial tissues, suggesting activity in these tissues. In men, studies of male reproductive health and soy consumption show no significant effect on concentrations of bioavailable testosterone. This includes total testosterone, sex hormone-binding globulin (SHBG), free testosterone, and the free androgen index. Soy also affects thyroid hormones. Genistein and daidzein appear to block thyroid hormone production by interfering with the iodination of thyroglobulin catalyzed by thyroid peroxidase. This action can lead to an increase in thyroid-stimulating hormone (TSH) and goiter, especially in people with low iodine levels, although this effect on thyroid function is generally not clinically significant in those with adequate iodine intake.
Usages associés
Cardiovascular
The soy isoflavones, particularly genistein, play a key role in soy's beneficial cardiovascular effects, helping to prevent cardiovascular disease through various mechanisms. Genistein inhibits the oxidation of LDL particles, a critical process in the early development of atherosclerosis. It acts as a free radical scavenger and inhibits cyclooxygenase (COX) activity, thereby reducing the formation of atherosclerotic plaques. In addition to preventing LDL oxidation, genistein also protects vascular cells from oxidized LDL and may prevent vascular remodeling, a key factor in plaque formation. Soy also appears to improve arterial compliance, particularly in postmenopausal women, and to lower blood pressure, especially diastolic pressure. Clinical evidence indicates that soy powder can reduce diastolic blood pressure by increasing levels of adiponectin and nitric oxide, the latter playing a role in blood pressure regulation. Finally, soy protein may reduce glucose levels due to its fiber content. Soy also improves glycemic control by inhibiting tyrosine kinase activity, enhancing insulin receptor affinity and glucose transport while increasing tissue sensitivity to insulin.
Usages associés
Anticancer
Soy isoflavones, phytoestrogens, are key compounds that play a major role in soy's anticancer properties. These compounds, notably genistein and daidzein, mimic the effects of endogenous estrogens and interact with estrogen receptors, acting both as estrogen agonists and antagonists. These interactions are particularly relevant in the contexts of breast and prostate cancer. Antiproliferative and Pro-apoptotic : Genistein, in particular, has been shown to inhibit cell proliferation and induce apoptosis in various cancer cell lines. It exerts these effects through cell cycle arrest and the induction of programmed cell death, which is crucial to prevent the proliferation of cancer cells. Hormonal Modulation : In the context of breast cancer, isoflavones modify the metabolism and activity of estrogens, which are critical factors in the development and progression of many hormone-sensitive cancers. By reducing estrogen production and altering the ratio of estrogenic metabolites in the urine, soy isoflavones can lower the risk of hormone-dependent cancers. Effects on Angiogenesis : Research also indicates that isoflavones can inhibit angiogenesis, the process by which tumors develop new blood vessels to support their growth. This mechanism helps limit tumors' ability to grow and metastasize. Aromatase Inhibition : Particularly relevant for breast and endometrial cancers, isoflavones inhibit the activity of aromatase, an enzyme that converts androgens into estrogens. This action can locally reduce estrogen levels, thereby lowering cancer risk in hormone-sensitive tissues. Effects on Tyrosine Kinase Receptors : Isoflavones also interfere with various enzymes and proteins involved in cellular signaling pathways, such as tyrosine kinases, which are essential for the growth and survival of cancer cells. For example, genistein can inhibit the activity of certain tyrosine kinases involved in the development of prostate cancer. Epidemiological studies have linked high soy consumption to a reduced risk of several types of cancer. However, despite these promising effects, clinical trial results are still insufficient to make definitive recommendations regarding their use for cancer prevention or treatment.
Usages associés
Bone density
Soy, because of its estrogenic effects, is considered beneficial for preventing postmenopausal osteoporosis. Like estrogens, soy appears to primarily influence the bone mineral density of the lumbar spine. It increases serum levels of osteocalcin, a marker of bone formation, in postmenopausal adults. The soy isoflavone genistein appears to directly inhibit the activity of osteoclasts, the cells responsible for bone resorption, and therefore could reduce bone turnover. In addition, high soy consumption appears to lower parathyroid hormone levels, which may also reduce bone turnover. In vitro tests suggest that genistein can promote osteoblast proliferation by inhibiting oxidative damage, further supporting new bone formation.
Usages associés
Antiandrogenic
Soy phytoestrogens, beneficial in prostate diseases, act through estrogenic mechanisms and inhibit the enzymes 5-alpha-reductase and 17-beta-hydroxysteroid dehydrogenase, reducing levels of estradiol and testosterone without affecting PSA levels.
Neurological
Soy isoflavones may benefit cognitive function, similar to estradiol, by upregulating choline acetyltransferase and nerve growth factor, which are essential for learning and memory. They may also decrease phosphorylation of the tau protein, which is associated with Alzheimer's.
Safe dosage
Adults 18 years and older: 50 mg - 90 mg (isoflavone-standardized extract)
Soy foods are available in various forms, including tofu, miso, and soy milk. nnThe soy protein is commonly used at doses up to 40 g per day for a maximum duration of 6 months. nnThe soy isoflavones have been used at doses up to 120 mg per day for a maximum duration of 6 months. nnThe optimal dose required to achieve clinical effects:nn- Soy protein: 15 to 20 g/daynn- Isoflavones: 50 to 90 mg/day.nnnnSoy foods contain variable amounts of isoflavones. Soy flour contains 1.3 mg/g of isoflavones, tofu 0.4 mg/g, soy milk 0.25 mg/g, tempeh 0.4 mg/g, miso 0.92 mg/g, soy sauce 0.023 mg/g, soy paste 0.57 mg/g, and soy cheese 0.05 mg/g. nnAlthough soybean oils and lecithin are used in many food ingredients, the typical Western diet provides a negligible amount of isoflavones, whereas Asian diets typically contain 20 to 50 mg of isoflavones. nn
Interactions
Médicaments
Antidiabetic: moderate interaction
Soy may lower blood glucose and have additive effects with antidiabetic medications.
Antihypertensive: moderate interaction
Soy may have additive effects with antihypertensive medications and increase the risk of hypotension.
Levothyroxine: moderate interaction
Soy-based products may reduce the absorption of levothyroxine in some patients.
Progesterone: moderate interaction
Clinical research suggests that significant bone loss can occur in women with osteoporosis who receive a combination of transdermal progesterone and soy milk containing isoflavones.
Tamoxifen: moderate interaction
Research indicates that genistein and daidzein, soy isoflavones, may interfere with tamoxifen's antitumor effects at low concentrations, but they may enhance its effects at higher doses.
Monoamine oxidase inhibitor (MAOI): strong interaction
Consumption of soy-based products that contain high amounts of tyramine while taking MAOIs may increase the risk of a hypertensive crisis. This is because MAOIs reduce the metabolism of tyramine.
Precautions
Pregnant women: use with caution
Soy consumption is considered safe for pregnant women when consumed in amounts commonly found in foods. However, the use of soy in medicinal amounts should be avoided as it contains components that are slightly estrogenic and could theoretically negatively affect fetal development.nn
Breastfeeding women: use with caution
During breastfeeding, soy consumption is also considered safe in amounts commonly found in foods. nnA single dose of 20 g of soy containing 37 mg of isoflavones results in four to six times lower isoflavone levels in breast milk than in a soy-based infant formula. nn
Hypothyroidism: avoid
Soy consumption may worsen hypothyroidism in patients with low iodine levels.
Kidney stones: avoid
Soy-based products may increase the risk of kidney stones due to their high oxalate content.
Bladder cancer: avoid
Soy-based products may increase the risk of bladder cancer. Avoid in patients at risk or with a history of bladder cancer.
