The health benefits of soya
A controversial food choice, but given soya is packed with protein and useful micronutrients, why is this versatile ingredient the subject of so much debate? Registered nutritionist Jo Lewin discovers more.
What is soya?
The soya bean plant is native to China, where it has been cultivated for well over 13,000 years. Like other beans, the soya bean (Glycine max) grows in pods enclosing the edible seeds. They are usually green, but may also be yellow, brown or black. The versatile texture of the bean means it may be processed into a variety of foods including a ‘milk’ and soya protein, as well as tofu, miso and tempeh. When eaten fresh from the pod, soya beans are often referred to as edamame beans.
An 80g serving of soya beans (boiled) provides:
- 113kcal / 472KJ
- 11.2g Protein
- 5.8g Fat
- 0.7g Saturated fat
- 4.1g Carbohydrate
- 6.5g Fibre
Top 5 health benefits
1. Source of protective antioxidants
Soya beans contain natural compounds called isoflavones. These polyphenols are powerful antioxidants and as such help minimise the damage known as oxidative stress, done by molecules called free radicals. It’s this oxidative stress which is involved in both aging and the onset of chronic disease. Soya beans are especially rich in isoflavones and provide other active plant compounds such as saponins.
2. May alleviate menopausal symptoms
Soya isoflavones (daidzein and genistein) have attracted a great deal of research and some studies even suggest that certain women with a soya-rich diet may experience a lower risk of breast cancer. This is in part because isoflavones are known as phyto-oestrogens; this means they mimic a weak form of the hormone oestrogen in the body. Some women find this helps with peri-menopausal symptoms such as poor mood and hot flushes.
Genetics, your gut microbiota and environmental factors play a huge part in how our bodies react to certain foods, so as yet, we can’t say whether a diet rich in phyto-estrogenic foods is beneficial for all women or not.
3. Source of ‘complete’ plant protein
Soya beans are a useful source of plant protein, providing all nine of the essential amino acids we need for growth, repair and functions like immunity. The digestibility of the protein in soya, which refers to how well our body can use the protein is good, with some studies suggesting it may even be comparable to that of animal protein.
4. May support heart health
Soya beans also contain compounds called phytosterols. These plant compounds are structurally similar to cholesterol and work in the body by inhibiting choleterols absorption. This explains why regularly eating foods like soya has been associated with reduced cholesterol levels. Studies suggest this includes a reduction in low-density lipoprotein (LDL), the type often referred to as ‘bad’ cholesterol, as well as total cholesterol.
Regular consumption of legumes, including soya beans, has also been linked to a lower risk of heart disease; this is thought to be because they are a rich source of phytochemicals as well as fibre.
5. May support bone health
Soya foods may be a beneficial inclusion for mid-life women; this is because lower levels of oestrogen after the menopause may lead to a greater reduction in calcium levels in the bone. Some studies suggest that including 40-110mg of soy isoflavones each day may reduce this bone loss and improve bone mineral density. From a practical perspective, this would be the equivalent to eating 140-440g of tofu or 35-100g of cooked soya beans each day.
Is soy safe for everyone?
Soy is generally recognised as safe for most people, unless you have a soy allergy, when it should be avoided. Soybeans are also considered to be goitrogenic, which means they interfere with the activity of the thyroid gland. Although in practice this effect may be minimal, if you have a thyroid condition you may wish to minimise your intake.
Soy products contain oxalate, and for this reason people with a history of calcium oxalate kidney stones may choose to avoid overconsuming soy products. However, studies suggest that soy products containing some oxalate and moderate amounts of phytates may actually be advantageous for kidney stone patients.
The consumption of soy has become controversial over recent years, with some animal studies suggesting a link with certain cancers. In support of the food’s safety, the European Food Safety Authority has concluded that soy isoflavones do not adversely affect the thyroid, breast or uterus in postmenopausal women.
Soya contains antinutrients including trypsin inhibitors and phytates; these may inhibit our absorption of some of the bean’s valuable nutrients. Soaking or fermenting the soybeans before cooking can minimise these compounds – this is why choosing traditional soya products, like tempeh and miso, can provide superior nutritional value.
Before changing your diet, it is advisable that you speak to your GP or alternative health professional.
Not just for vegetarians, soya beans go well with chicken too:
Chicken, edamame & ginger pilaf
This article was last reviewed on 6 October 2021 by Kerry Torrens.
Kerry Torrens is a qualified nutritionist (MBANT) with a postgraduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the past 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
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