Search ‘soy’ on the world wide web and you’ll uncover mixed messages about its’ health benefits. One search response will sing its praises for reducing cholesterol, helping menopausal symptoms and reducing risk of cancer. The very next search response will suggest it causes cancer, infertility and thyroid dysfunction. Which begs the question, should you eat soy?
I believe the humble soybean never meant to cause so much confusion, yet it does and it’s a hotly debated topic in the field of health and nutrition. In this article I wanted to uncover the research, get to the facts on soy and bring some awareness as to how it can very safely form part of the diet.
Soy 101
At the most basic level, soy is a legume. It comes from the same family as chickpeas, butter beans, kidney beans and lentils yet with a marked difference in macronutrient profile. It’s much higher in fat, lower in carbohydrate and higher in protein than the rest of the legume family however what really makes it common place in any plant-based diet is the quality of the protein. Soy contains all essentials amino acids making it what we call a ‘complete protein’ and therefore comparable to animal protein sources. The lower carbohydrate nature of soy is what lends it so nicely to a lower carbohydrate, healthy fat and whole food approach to plant-based nutrition.
Soy contains all essentials amino acids making it a ‘complete protein’ and therefore comparable to animal protein sources.
The many forms of soy
From a Nutritionists perspective there’s soy, and then there’s soy. What I mean is that there are two distinct categories of soy products. The first are whole food products, where the degree of processing is minimal. In this category would be unfermented products such as tofu, soy milk and edamame as well as fermented soy products including tempeh, natto, soy sauce and miso. The second category of processed soy products includes soy cheeses, soy yoghurt and “meat” products.
Health considerations
As I highlighted at the start of the article, there are many claims made about either the health promoting or health depleting effects of soy. By in large, these are associated with a specific compound found within soy: isoflavones. Isoflavones are a class of flavonoid (also found in flaxseeds and chickpeas) which exhibit antioxidant, antimicrobial and anti-inflammatory properties. They can also act as phytoestrogens which are compounds that have the potential to bind to estrogen receptor sites on the body.
Before detailing any specific health considerations, I want to draw your attention to a 2019 review. In this review they assessed the existing evidence of associations between consumption of soy isoflavones and various health outcomes. It was an umbrella review of meta-analyses and systematic reviews of randomized trials and observational studies in humans. In total 114 meta‐analyses and systematic reviews were identified with 43 unique outcomes. The study concluded that soy isoflavone consumption was more beneficial than harmful and that beneficial associations are identified specifically with cancers, cardiovascular disease, gynaecological, metabolic, musculoskeletal, endocrine, neurological, and renal outcomes, particularly in perimenopausal women. The only harmful association found was for gastric cancer in one male who was consuming 1 – 5 cups of miso soup per day.
The study concluded that soy isoflavone consumption was more beneficial than harmful...
Cardiovascular disease
The findings from a 2017 meta-analysis suggest that eating more soy foods is linked to a significantly lower risk of cardiovascular disease, stroke and coronary heart disease. However, we know that correlation does not equal causation so it’s very possible that other areas of the diet could have influenced, such as a higher fibre diet or more antioxidant rich diet. All of which are achieved on a lower carbohydrate, healthy fat and whole food plant based approach to nutrition.
Perimenopause
A review of 16 double-blind studies quantified the effects of isoflavones and found that in terms of frequency and severity of hot flushes in menopausal women, isoflavones were 25 – 26% more effective than placebo.
Thyroid
Depending on your information source, soy may come up as a food to avoid in conditions of hypothyroidism (underactive thyroid). This is because soy contains goitrogens (as do foods like broccoli, kale and cabbage) which have the potential to interfere with thyroid hormone production by inhibiting the uptake of iodine into the thyroid gland. This can be an issue as iodine is a key part of thyroid hormone production. In saying this, the literature surrounding soy consumption and thyroid function doesn’t suggest there’s any need for concern in those with adequate iodine status. So in short, unless you’re on thyroxine (synthetic thyroid hormone) there’s little evidence to show that consumption of soy will have any detrimental effects and if you’re at all at risk, maintain adequate iodine intake from foods like wakame, nori, dulse flakes and even iodised salt.
Safely including soy in the diet
Type
Let’s be clear - I only recommend the inclusion of whole food soy products and if you’ve explored my recipes at all, you’ll see those featuring most frequently include tempeh, tofu and miso.
Tempeh: At the top of the recommended list is tempeh. This is a product of whole soybeans being inoculated with a fungus and left to ferment for a few days. The end product is firm in texture and nutty to taste. The flavour can be quite polarising however in my clinical experience people quickly adjust to the flavour and note that it tends to be better digested than tofu. If you haven’t cooked with tempeh before, you might like to check out these Crispy Tempeh Bites or the Three Greens with Tempeh Gems.
Tofu: It’s made using soy milk and a coagulant, similar to the process of making cheese. It comes in various textures (from firm to soft) and the flavour is mild, which is why some prefer this over tempeh. The most talked about and viewed recipe on my site is this Gado Gado Bowl.
Miso: it’s the by-product of fermented soy beans being blended and packaged to create a paste. The paste can be mixed with hot water to create a beautiful stock (or soup) or it can be blended with other products to create a low sugar salad dressing. Try this Miso Dressing.
Amount
100 – 150g servings of tofu or tempeh (smaller for females and larger than males) can be included as frequently as 4 – 6 times/week. Miso consumption tends to be self-managed as I haven’t met anyone who’d willingly consume more than a few tbsp per week.
If you have a thyroid condition please seek tailored advice on the amount of tofu or tempeh appropriate for you and your goals. In saying this, if you have a thyroid condition and haven’t sought nutrition support before then I’d highly recommend that you do!
I hope this article has helped to clear any confusion you may have had about soy! Consume wisely and enjoy the recipes I’ve shared.
If you have any questions regarding your own requirements for soy, thyroid health or digestive health then I would love to work with you. You can get started by booking a 15-minute Complimentary Consultation.
References:
Li N, et al. 2020. Soy and Isoflavone Consumption and Multiple Health Outcomes: Umbrella Review of Systematic Reviews and Meta‐Analyses of Observational Studies and Randomized Trials in Humans. Molecular Nutrition & Food Research, 64, 1900751.
Zhaoli Y, et al. 2017. Association between consumption of soy and risk of cardiovascular disease: A meta-analysis of observational studies. European Journal or Preventative Cardiology, 24, 7, 735 – 747.
Jiu Y, et al. 2016. Isoflavones: Anti-Inflammatory Benefit and Possible Caveats. Nutrients, 8, 6, 361.
Messina M and Redmon G. 2006. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid, 26, 3, 249 – 258.
Franco OH, et al. 2016. Use of plant-based therapies and menopausal symptoms: a systematic review and meta-analysis. Journal or American Medical Association, 315, 23, 2554-2563.
Taku K, et al. 2012. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials.Menopause, 19, 7, 776-790.