Soya myth busting

Viva! Health examines the soya scare-mongering stories and investigates what, if any, scientific basis there is behind them.

  1. Soya disrupts thyroid function
  2. Processed soya foods are bad for you
  3. Soya makes you get man boobs
  4. Soya milk is a new Western invention

1. Soya disrupts thyroid function For the vast majority of people, soya does not disrupt thyroid function. If you're basically healthy, your thyroid is functioning properly and you get enough iodine in your diet, you are extremely unlikely to be affected.

The thyroid is a small gland found in the front of the neck which produces a hormone called thyroxine, which helps to control how fast the body makes and uses energy from food.  The thyroid gland needs iodine to make thyroxine and a lack of iodine can cause it to enlarge, forming a goitre.

The concerns about soya and thyroid are based on two issues - the presence of goitrogens and soya isoflavones or plant hormones.

Goitrogens occur naturally in soya, broccoli, kale, cabbage, turnips, millet, peanuts and pine nuts and can interfere with the uptake of iodine, which in turn can lead to the formation of a goitre. This only becomes a problem if the diet fails to provide enough iodine. 

How soya isoflavones act on the thyroid – if at all – isn't clear. A recent review of 14 studies found that there was little evidence that soya foods or their isoflavones adversely affect thyroid function in healthy people whose diets contain enough iodine.

As a precautionary measure, health practitioners are warned that people whose thyroid isn't fully functional, and/or whose iodine intake is marginal, may require higher doses of thyroid medication and that soya foods may predispose these susceptible individuals to hypothyroidism (underactive thyroid).

Given the lack of clinical evidence, these concerns are mostly theoretical but the general consensus is that everyone, soya consumers or not, should ensure they get an adequate intake of iodine. One of the simplest ways is to use iodised salt.

The government recommends 140 micrograms of iodine per day for adults and good sources include seaweed such as nori and kelp, Vecon vegetable stock or iodised salt.  Iodine can also be found in cereals and grains but levels vary depending on the amount of iodine in the soil.

Too much iodine because can be harmful and the Food Standards Agency reckon that 500 micrograms or less a day is unlikely to cause harm.

2. Processed soya foods are bad for you 
Generally speaking, the more processed a food becomes, the less nutritional value it has. For example, there is significantly less fibre, vitamins and minerals in white bread than wholemeal bread. It's also true that traditional Asian soya foods such as tofu, miso, tempeh, soya sauce, tamari and soya milk, made using fermentation or precipitation methods, contain a wider range of nutrients than modern soya protein isolates such as textured vegetable protein (TVP) used in mock meats.

The soya antis claim that Western soya products are so highly-processed that they lose valuable nutrients and the plant hormone content (isoflavones) may be increased.

The truth is that ‘mock meats' still provide a valuable, low-fat and cholesterol-free source of good protein and so remain a healthier option than their meaty equivalents, which contain saturated animal fat, animal protein and cholesterol. They are also a source of hormones such as oestrogen and animal hormones are far more potent than plant hormones, having been linked to certain cancers.

Despite this, the Viva!Health do not recommend the excessive consumption of highly-processed foods of any kind – soya or not - as they tend to contain high levels of fat, often including hydrogenated fat, salt, sugar and artificial additives.  The key to good health is to eat a wide range of foods, including plenty of whole grains such as wholemeal bread, brown pasta and brown rice, pulses such as peas, beans and lentils, fruit and vegetables, nuts and seeds.

3. Soya makes you get man boobs
This myth is solely based on animal experiments which suggest that phytoestrogens (plant hormones in soya) can affect sexual development and reproductive function.

These experiments are fundamentally flawed on many levels. Firstly, phytoestrogens behave differently in different species so animal studies bear no relevance to humans. Secondly, artificially boosting levels in animals by injection has no relevance. Finally, many of these experiments have exposed animals to phytoestrogen levels many, many times higher than those absorbed by humans eating soya.

More and more scientists and doctors are acknowledging that the results of animal experiments bear little or no relevance to human health. Use a bit of common sense here; millions of infants have been raised on soya formulas in the UK and US, (25% of US infants are raised on soya formula) many of whom are now well into their late 30s and early 40s.

What's more, there are no reports from Japan and China that the use of soya has affected fertility rates.

Viva!Health are far more concerned about the effects of consuming the animal hormone oestrogen in cow's milk.
See the White Lies report.      

4. Soya milk is a new Western invention
Soya milk originated in China where the beans have been used as food far longer than the existence of written records. Soya milk is reputed to have been discovered and developed by Liu An of the Han Dynasty in China about 164 BC. That's over 2,000 years ago. So you can see, it is not a new invention by any means.