Nutritionist Rishi Kumar Nursimloo addresses the misnomers surrounding soya
Soya foods have been consumed in traditional Asian populations for thousands of years. However, in many other populations, there have been many concerns surrounding the consumption of soya; it is bad for me? Can I over-consume soya? Will it increase my male breast tissue? To answer these questions, we have summarised the current literature on the effects of soy on our health.
The Science of Soy
Soybeans and soy products contain a plant-derived compound called isoflavones, which are a class of phytoestrogens (plant based estrogens). Whilst you may be concerned when discussing the hormone oestrogen, these specific compounds (phytoestrogens) actually provide beneficial oestrogenic and anti-oestrogenic effects.
Oestrogen receptors are present in many tissues and these isoflavones bind to and trans-activate oestrogen receptors. This means they mimic the effects of oestrogen in some tissues and block the effects of oestrogen in others. It is these two effects that spark scientists interest as oestrogenic effects may help in maintaining bone health, reduce the likelihood of coronary heart disease and the anti-oestrogenic effects may help in reduce the risk of hormone-associated cancers.
Some observational and clinical studies have shown a link between soya intake and improved bone health, especially in Asian women. People who regularly eat soya appear to have higher bone density and lower rates of fracture than those with low intakes. Research is in this area is on-going and dietary interventions are not considered a replacement for anti-osteoporotic medication.
Lactose intolerance affects around 5 per cent of the UK adult population, along with other adverse effects in comparision to cows milk. Consumption of dairy and lactose-free alternatives are suitable for children over six months of age and adults with lactose intolerance (around) and with. As a general guideline, ensure when replacing dairy that soya products are fortified with calcium.
Both diets high in saturated fat and having too much low-density lipoprotein (LDL) or ‘bad’ cholesterol in the blood are major risk factors for coronary heart disease. Consuming soya foods as part of a healthy low-saturated fat diet, which is typical in a vegan diet, can help lower LDL cholesterol and therefore lower our risk of heart disease. One way that soya can help in reducing LDL cholesterol is by lowering the body’s natural cholesterol-producing capacity in the liver. Additionally, the replacement of foods high in saturated fat such as fatty meat and full fat dairy products with soya foods, which are naturally low in saturated fat, contributes to higher unsaturated fat intake, helping to reduce LDL cholesterol.
These changes can lower LDL cholesterol by as much as 10 per cent if you eat 15-25g soya protein per day — approximately two glasses of soya milk.
Research has also highlighted the benefits of combining soya protein with other plant foods in aims to reducing LDL cholesterol, such as nuts, plant sterols/stanols and beta-glucan rich foods, such as oats or barley. Cholesterol levels can be reduced by as much as 12-24 per cent, depending on the types and amounts of these foods consumed.
Atherosclerosis (fatty build-ups in your arteries) and thrombosis (blood clots) are two key processes in the development of cardiovascular disease. There are some small studies which show that soya isoflavones may help improve the flexibility and function of the lining of key blood vessels but despite great potential, more research is currently needed in this area to prove this theory.
Studies consistently show that eating soya foods does not raise oestrogen levels, reduce testosterone, upset hormonal balance or concentrations in men. Furthermore there are no reports to show soya had adverse effects on fertility or sexual health, such as erectile dysfunction or feminisation and thorough peer reviews of the literature have found no basis for concern. However, in the long term, comprehensive human studies are needed.
In healthy individuals with a normal functioning thyroid gland, the latest review of 14 studies has confirmed that there is no harmful effect of soya food consumption. However the exception to this appears to be people suffering with an underactive thyroid gland (hypothyrodism), as the consumption of soya isoflavones can inhibit with the absorption of synthetic thyroid hormones. A recent study has indicated that soya isoflavones may worsen the condition for individuals with a mildly underactive thyroid. Therefore, according to the British Dietetic Association, if you have thyroid issues and would like to want to consume soya foods, consult with your doctor and get your thyroid levels checked.
Soya and Cancer
The benefits of choosing plant based proteins in comparison to animal protein are massive and well known to the vegan community. IGF-1 (Insulin Growth Factor 1) is a hormone heavily associated with increased cancer risk. A study which compared meat-eaters to vegans showed that the association between protein intake and higher IGF-1 levels were only associated with animal protein intake. Consumption of plant proteins seemed to decrease IGF-1 levels, which therefore lowers the level of the cancer promoting growth hormone in comparison to meat.
Many countries with high soya intakes also have a low rate of hormone-associated cancers, such as breast, prostate and endometrial (uterine). Some studies suggest that lifelong soya consumption and exposure to isoflavones — especially before and during puberty — may protect against the development of breast cancer, the most common cancer in the UK, and other studies suggest that intakes of soya isoflavones, ≥10 mg/day, was associated with a 25 per cent reduced risk of tumour recurrence in breast cancer survivors. Furthermore, soy food consumption has been associated with a reduced risk of prostate cancer, the most common form of cancer in males in the US.
In terms of increased breast cancer risk, one study by the American Institute for Cancer Research (AICR) in 2012 found that there are no indications that eating soya is unsuitable for people at risk of breast cancer, breast cancer patients, for survivors of breast cancer, or those with an increased risk of breast cancer. The AICR latest review research indicates that soya isoflavones may in fact lower the risk of cancer, in some cases.
Soya and Menopausal Symptoms
Many women undergoing the menopause experience symptoms of hot flushes, which are believed to result from fluctuations in the brain’s temperature-regulating system as a consequence of the decline in the production of oestrogen, which raises cholesterol level and increased risk of cardiovascular disease as much as 25 per cent. Having two servings of soya foods daily can help with both lowering cholesterol and reductions in the severity of hot flushes.
In observational studies, up to 75 per cent of Western women experience hot flushes, whilst only around 20 per cent of Japanese and Chinese women, who consume a traditional diet based on soya foods, experienced the same symptom. In comparison to Western women, the Chinese group consumed around 10-20 times the amount of isoflavones (15-40mg per day).
Several studies show that consuming around 50-80mg soya isoflavones daily for 8-12 weeks can help lower both the frequency and severity of hot flushes by a quarter. The benefit seems to be gained by women who experience at least five severe hot flushes daily. 50mg isoflavones can be achieved by consuming around two to three servings of soya foods daily.
To this day, according to the British Dietetic Association, Hormone Replacement Therapy (HRT) is still the most effective treatment of menopausal symptoms, and you should consult your healthcare professional about HRT.
In conclusion, consumption of soya foods are completely safe for men and women throughout all stages of life and indications of any potentially harmful effects from isoflavones have not been shown in humans. The safety of soya has been thoroughly reviewed and soya foods are permitted for use in the UK under the Food Safety Act. If you do have any concerns, please visit a dietician or registered nutritionist for further information.