Soy: benefits, dosage, contraindications
Other name(s)
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Scientific name(s)
Glycine max
Family or group:
Plants
Active ingredients:
Isoflavones
Calcium
Iron
Potassium
Indications
Rating methodology
EFSA approval.
Menopause ✪✪✪✪✪
Soy isoflavones are considered for reducing menopause symptoms, particularly hot flashes. Meta-analyses and clinical studies indicate that consuming soy protein providing 34 to 100 mg of isoflavones per day moderately reduces the frequency and severity of hot flashes, especially in women with initially frequent flashes. Controlled trials suggest that concentrated soy isoflavone extracts, at doses of 35 to 200 mg per day, are comparable to conventional estrogen for reducing menopause symptoms. One study showed that a genistein extract at 54 mg per day reduced hot flashes by 22% to 29%, compared to 54% with 1 mg of daily estradiol. Recent research reveals that regular soy consumption might also improve other menopause symptoms like vaginal dryness and skin hydration. However, effects on breast density and cancer risk remain inconclusive, and the effectiveness of soy may vary based on individual 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 in preventing breast cancer and its recurrence in certain patients. A meta-analysis revealed that those consuming more than 15 mg of soy isoflavones per day comprised about 25% of all breast cancer cases, compared to 75% among those consuming less than 15 mg per day. This effect varies among groups, with Asian and Asian-American women benefiting from a significantly reduced risk. In the West, even among those consuming 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 using soy isoflavone extracts (200 mg/day for 2 weeks before surgery or 50 mg/day for 12 months) showed no significant effect on cancer cell growth or breast density.
Posologie
Oral
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
Phyto-oestrogen 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 to a control. However, lower doses seem 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. Nonetheless, some contradictory results exist. It might be that only those capable of converting daidzein, a soy isoflavone, into S-equol (a metabolite) can benefit from soy.
Posologie
Oral
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 post-menopausal 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 to a placebo. A meta-analysis of three clinical studies shows that soy protein consumption improves strength and lean muscle mass in untrained athletes. Other clinical research also indicates improvements in menopausal women. A study on endurance Olympic 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 maximum lifted strength in leg press and extension exercises in menopausal women. Compared with other protein supplements like whey, beef, and dairy products, soy protein seems equally effective in enhancing muscle strength, although the validity of these results is limited by study quality.
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 serves as an effective alternative to cow's milk for individuals with lactose intolerance. It can be used in infant formulas to prevent lactose intolerance symptoms. Specifically, formulas based on isolated soy protein are an acceptable option for at-risk infants.
Posologie
Oral
soy milk
Metabolic Syndrome ✪✪✪✪✪
A meta-analysis on diabetic patients or those with metabolic syndrome reveals that adopting a diet rich in soy protein can reduce fasting plasma glucose, insulin levels, and insulin resistance compared to a control diet. Other clinical studies indicate that a soy protein-based diet reduces fasting plasma glucose and LDL cholesterol in postmenopausal women.
Posologie
Oral
120 mg
standardized isoflavone extract
Dyslipidemia ✪✪✪✪✪
The use of soy proteins, replacing other dietary proteins, seems to modestly reduce total cholesterol and LDL cholesterol by about 3% to 4% compared to a control group. In the US, for soy products to be eligible for the cholesterol claim, they must provide at least 6.25 g of soy protein per serving. However, results vary: some studies show enhanced efficacy in patients with more severe hyperlipidemia, while others observe no significant benefits on LDL or triglyceride levels compared to control. Soy protein doses used in 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.
Posologie
Oral
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 seem to reduce the risk of type 2 diabetes, and soy proteins, unlike isoflavones, modestly improve glycemic indices. A meta-analysis of observational studies revealed that high consumption of tofu, soy proteins, or soy isoflavones is associated with an 8% to 16% reduction in the risk of developing diabetes compared to low consumption. Additional research shows that soy may modestly improve lipid profiles in diabetics, slightly reducing total cholesterol and LDL levels over periods of 6 to 12 weeks, without affecting HDL cholesterol or triglyceride levels. Furthermore, regular soy consumption could reduce the risk of cardiovascular mortality in diabetic patients, with research suggesting that consuming soy at least four days a week is associated with a 23% reduction in the risk of cardiovascular mortality.
Posologie
Oral route
40 - 161 mg
standardized extract in isoflavones
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
Hypertension ✪✪✪✪✪
Several meta-analyses have shown that the consumption of soy-based products slightly reduces systolic and diastolic blood pressure in patients with pre-hypertension or mild hypertension. The studied formulations contain 18 to 40 g of soy proteins, 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 the high risk of bias and the lack of dose-response relationship. In normotensive patients, the intake of soy proteins does not appear to reduce blood pressure.
Posologie
Oral route
118 - 143 mg
standardized extract in isoflavones
Properties
Hormonal metabolism
Soy isoflavones, notably genistein and daidzein, are phytoestrogens structurally similar to endogenous estrogens and act as selective modulators of estrogen receptors. These components have the capability to weakly bind to estrogen receptors alpha and beta, although genistein exhibits a binding affinity comparable to that of 17-beta estradiol. This interaction partly explains the protective effects of soy against cardiovascular diseases, certain cancers, and menopausal symptoms. Isoflavones exert complex and tissue-specific actions, sometimes acting as partial estrogen agonists and antagonists. Furthermore, they influence plasma membranes and cell signaling pathways in a non-classical manner. Interestingly, isoflavones have a greater affinity for the beta estrogen receptor, present in the brain, bones, and vascular epithelial tissues, which suggests activity in these tissues. On the male side, studies on male reproductive health and soy consumption show no significant effects on the concentrations of bioavailable testosterone. This includes total testosterone, sex hormone-binding globulin, free testosterone, and free androgen index. Soy also exerts an action on thyroid hormones. Genistein and daidzein appear to block thyroid hormone production by interfering with thyroperoxidase-catalyzed iodination of thyroglobulin. This action can lead to increased thyroid-stimulating hormone (TSH) and a 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
Soy isoflavones, particularly genistein, play a key role in the cardiovascular benefits of soy, helping to prevent cardiovascular diseases through various mechanisms. Genistein inhibits the oxidation of LDL particles, a crucial process in the early development of atherosclerosis. It acts as a free radical scavenger and inhibits the activity of cyclooxygenase (COX), thus 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 element in the formation of atherosclerotic plaques. Soy also appears to improve arterial compliance, especially in postmenopausal women, and lower blood pressure, particularly diastolic pressure. Clinical evidence indicates that soy powder can reduce diastolic blood pressure by increasing adiponectin levels and nitric oxide, the latter playing a role in blood pressure regulation. Finally, soy protein could reduce glucose levels thanks 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 the anticancer properties of soy. These compounds, especially genistein and daidzein, mimic the effects of endogenous estrogens and interact with estrogen receptors, functioning as both estrogen agonists and antagonists. These interactions are particularly relevant in the contexts of breast and prostate cancers. Antiproliferative and Pro-apoptotic: Genistein, in particular, has demonstrated capabilities to inhibit cell proliferation and induce apoptosis in various cancer cell lines. It exerts these effects through cell cycle arrest and stimulation of programmed cell death, which is crucial for preventing the multiplication of cancer cells. Hormonal Modulation: In the context of breast cancer, isoflavones modify estrogen metabolism and activity, which are critical factors in the development and progression of many hormone-sensitive cancers. By reducing estrogen production and altering the ratio of estrogen metabolites in urine, soy isoflavones can reduce the risk of hormone-dependent cancers. Effects on Angiogenesis: Research also indicates that isoflavones may inhibit angiogenesis, the process by which tumors develop new blood vessels to support their growth. This mechanism helps to limit the ability of tumors to grow and metastasize. Aromatase Inhibition: Particularly relevant for breast and endometrial cancers, isoflavones inhibit aromatase activity, an enzyme that converts androgens into estrogens. This action can locally reduce estrogen levels, thus decreasing the 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 prostate cancer development. Epidemiological studies have linked high soy consumption to a reduced risk of several cancer types. However, despite these promising effects, the results of clinical trials are still insufficient to make definitive recommendations regarding their use in cancer prevention or treatment.
Usages associés
Bone density
Due to its estrogenic effects, soy is considered beneficial in preventing post-menopausal osteoporosis. Like estrogens, soy appears to primarily influence lumbar spine bone mineral density. It increases serum levels of osteocalcin, a marker of bone formation, in postmenopausal adults. Soy isoflavone, genistein, seems to directly inhibit the activity of osteoclasts, the cells responsible for bone resorption, and therefore could reduce bone turnover. Moreover, high soy consumption seems to decrease parathyroid hormone levels, which could 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 prostatic diseases, act through estrogenic mechanisms and inhibit the enzymes 5-alpha-reductase and 17-beta-hydroxysteroid dehydrogenase, reducing estradiol and testosterone levels without affecting PSA levels.
Neurological
Soy isoflavones may benefit cognitive function, similar to estradiol, by up-regulating choline acetyltransferase and nerve growth factor, crucial for learning and memory. They could also decrease tau protein phosphorylation, linked to Alzheimer’s.
Safety dosage
Adult from 18 years: 50 mg - 90 mg (standardized extract in isoflavones)
Soy-based foods are available in various forms, including tofu, miso, and soy milk. Soy protein is commonly used at doses of up to 40 g per day for a maximum duration of 6 months. Soy isoflavones have been used at doses of up to 120 mg per day for a maximum duration of 6 months. Optimal dose required to achieve clinical effects: - Soy proteins: 15 to 20 g/day - Isoflavones: 50 to 90 mg/day. Soy-based foods contain varying 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. Although soy oils and lecithin are used in many food ingredients, the typical Western diet provides a negligible amount of isoflavones, while Asian diets generally contain 20 to 50 mg of isoflavones.
Interactions
Médicaments
Antidiabetic: moderate interaction
Soy may reduce blood glucose levels and have additive effects with antidiabetic medications.
Antihypertensive: moderate interaction
Soy could have additive effects with antihypertensive medications and increase the risk of hypotension.
Levothyroxine: moderate interaction
Soy-based products could reduce the absorption of levothyroxine in some patients.
Progesterone: moderate interaction
Clinical research suggests that significant bone loss may occur in women with osteoporosis receiving a combination of transdermal progesterone and soy milk containing isoflavones.
Tamoxifen: moderate interaction
Research indicates that genistein and daidzein, soy isoflavones, may interfere with the antitumor effects of tamoxifen at low concentrations, but they may enhance its effects at higher doses.
Monoamine oxidase inhibitor (MAOI): strong interaction
Consuming soy products containing high amounts of tyramine with MAOIs may increase the risk of hypertensive crisis, as the metabolism of tyramine is decreased by MAOIs.
Precautions
Pregnant woman: 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 slightly estrogenic components that could theoretically negatively affect fetal development.
Breastfeeding woman: use with caution
During breastfeeding, soy consumption is also considered safe in amounts commonly found in foods. A single dose of 20 g of soy containing 37 mg of isoflavones produces four to six times less isoflavones in breast milk than in a soy-based infant formula.
Hypothyroidism: avoid
Soy consumption could worsen hypothyroidism in patients with low iodine levels.
Kidney stone: avoid
Soy-based products could increase the risk of kidney stones due to their high oxalate content.
Bladder cancer: avoid
Soy-based products could increase the risk of bladder cancer. Avoid in patients at risk or with a history of bladder cancer.
