So this is my third and final piece on soy (for the time being). If you missed Part 1 – genetically modified soy and phyto-oestrogens (click here) and Part 2 – manufacturing and processing (click here).
In this article I am focussing on how soy can impact thyroid function, cardiovascular systems and osteoporosis without getting too technical.
How does soy impact our thyroid?
Our thyroid gland is two lobes of glandular tissue located in the throat which produces thyroid hormones T4 and T3 amongst other thyroid hormones. It has been shown that soy can impair iodine absorption. Iodine is an essential trace element necessary for human growth, concentrated in the thyroid gland and used by the thyroid to produce the thyroid hormones. High levels of the isoflavones genistein and daidzen can inhibit T4 and T3 production, these being highest in soy. Other foods that contain genistein and daidzen (in higher levels but not as high as soy) include other legumes, currants and raisins, alfalfa and red clover. The majority of foods when cooked in boiling water decreases the genistein and daidzen content of foods.
Some menopausal products on the market contain high levels of genistein and daidzen which are extremely beneficial for menopausal symptoms. Studies show that although genistein and daidzen do inhibit thyroid peroxidise, there is not enough effect on the free thyroid hormones. Therefore a phyto-oestrogen dietary supplement would not be associated with the development of thyroid disorders if there is adequate iodine intake in the diet. If you have an underactive thyroid or any thyroid health concerns then avoiding soy might be an option for you, but most important is your iodine status. If you have adequate iodine levels in your body you could enjoy soy in small amounts. If you have an overactive thyroid then soy could perhaps help to reduce excess iodine if this applies to you.
Soy is extremely beneficial for our heart health!
Because soy is rich in isoflavones, protein, polyunsaturated fatty acids and are high in soluble fibre they have been shown to have positive effects on cardiovascular health with studies suggesting soy foods may prevent or delay cardiovascular disease development.
Soy protein has been shown to reduce total cholesterol, triglycerides, particularly the “bad” cholesterol (LDL) with limited impact on the “good” cholesterol (HDL). Some studies have shown that soy can help increase HDL cholesterol. Soy, being a complete protein, can be a great alternative to meat products when trying to reduce cholesterol.
Research has also shown that more than 25g of soy consumed per day was associated with reductions in systolic and diastolic blood pressure especially in women over 60 years of age.
Osteoporosis and Soy
Soy has been shown to significantly inhibit bone resorption and stimulates bone formation in menopausal women. Most studies have shown that soy can increase bone mineral density (BMD) in the spine with not enough studies yet completed on BMD of the hip. Soy has been shown to help reduce fracture risk of post menopausal women, although consuming soy during peri menopause and early menopause will have a greater effect on bone loss than waiting until post-menopause. Soy should be used in conjunction with other osteoporosis treatments to receive the most benefit.
Side note – Soy does contain phytic acid which can potentially bind to certain minerals such as calcium, magnesium, manganese, zinc, copper and iron so if you are concerned take these mineral supplements 2 hours away from when you have your soy products. Soybeans do naturally contain high levels of calcium, iron, potassium and phosphorus so this needs to be taken into account.
Hopefully you are feeling a bit more relaxed and positive towards soy if you have been starting to get a bit confused by the conflicting information that is out there about soy. My opinion is that most people can safely include organic soy products in their diet in moderate amounts.
*References available upon request
Megan is a qualified nutritionist who specialises in digestive issues, food allergy testing, women’s health and creating eating plans to suit and address many health conditions and/or intolerances.