Should You Eat Soya?

Once considered a superfood, soya has recently been linked to health issues. Is it harmful, or does it deserve a place in your diet? Shape investigates.

Portrait of Tammy Strobel

Once considered a superfood, soya has recently been linked to health issues. Is it harmful, or does it deserve a place in your diet? Shape investigates.

Photo Travis Rathbone
Photo Travis Rathbone

These days, it seems we’re all afraid to eat soya. It’s forbidden in popular eating plans like paleo. It has been blamed for fatigue, stomach disorders, weight gain, hormone problems, and even cancer. No wonder food manufacturers are labelling their products “soya-free”. It has become the new gluten. But hold on! Don’t get scared by the rumours; it does have real health and nutrition benefits, top experts say. Here’s the latest science.

Truth #1

Soya doesn’t cause breast cancer. There’s a common misperception that soya contains oestrogen and leads to breast cancer, says Anna Taylor, a dietitian at the Cleveland Clinic in the US. This false notion started because two isofl avones in soya, genistein and daidzein, are chemically similar to oestrogen.

That raised concerns among experts that soya might accelerate the growth of certain breast tumours, as oestrogen does. Then, a few years ago, alarm bells went off when rats with breast cancer that were given large amounts of genistein or daidzein had faster-growing tumours than rats who weren’t given any.

While this sounds serious, these isoflavones act differently in rats than they do in people, says Alice Bender, a dietitian at the American Institute for Cancer Research. Numerous epidemiological studies of women, in which participants reported their eating habits and were tracked over time, found either no connection between soya and breast cancer or a protective one, Alice explains. For example, a recent review of 14 epidemiological studies showed that women in Asia who regularly ate the most soya had a 54 per cent lower risk of developing breast cancer than those who ate the least. SHOULD YOU EAT

Truth #2

Eating soya won’t throw your hormones out of whack. Despite rumours, a recent US study by the University of Illinois found that soya hardly aff ects our hormones. An exception: If you take medication for hypothyroidism – a condition in which your body produces low levels of thyroid hormones – soya can interfere with your ability to absorb the drugs, so you need to wait four hours after taking your prescription to consume anything with soya, says endocrinologist Dr Jeffrey Garber, an associate professor of medicine at the US-based Harvard Medical School.

Similarly, a tofu habit won’t make it tougher to get pregnant. Though some animal studies have suggested that soya could reduce female fertility, and another study showed that men who ate it daily had a reduced sperm count, newer research has refuted those findings.

Truth #3

Soya foods are among the best vegetarian sources of protein. Vegetables, whole grains, and beans all have protein, but soya is one of the only vegetarian proteins that is considered complete, which means it has all the essential amino acids your body needs, Anna says. And 110g of tofu have about as much protein as a serving of steak! Plus, these foods help your heart. In a recent Dutch study, women who replaced some of the animal protein in their diets with soya saw their cholesterol levels and insulin sensitivity improve.

Truth #4

You’re probably not allergic or even sensitive to soya. Though some clean-eating plans suggest that if you eliminate soya from your diet, you’ll lose weight, have fewer headaches, and feel less fatigued, experts say any exhaustion or digestive ills you’re experiencing probably have nothing to do with the food. In fact, less than 0.5 per cent of the adult population is allergic to it.

It’s also highly unlikely that you’re soya-intolerant, says Dr James Sublett, president of the American College of Allergy, Asthma and Immunology. People tend to feel better after cutting out soya because they’re eating fewer processed foods, he explains. If you truly think you’re allergic – symptoms include hives, an itchy mouth, vomiting or diarrhoea, and wheezing – see an allergist for a skin test.



● EDAMAME These boiled or steamed soya beans are high in fibre, protein, vitamins, and minerals.

● SOYA MILK A small amount of nutrients may be lost in processing, but most soya milk is fortified with vitamins like B12 and D. And it contains as much protein as cow’s milk.

● TOFU Made by curdling soya milk, tofu is a great source of omega-3 fatty acids and calcium. Brands that list calcium sulphate as an ingredient have even more of the mineral.

● TEMPEH AND MISO These fermented foods contain bacteria that promote digestive health.

● SOYA NUTS Dried and roasted soya beans have more protein and fibre than classic mixed nuts.


● FOODS WITH ADDED SOYA PROTEIN In processing, soya protein is stripped of many nutrients, including ones with potential anti-cancer properties. Check labels for “soya protein,” “textured soya protein” or “soya protein isolate.”

● SOYA SAUCE It has more than 1,000mg of sodium per tablespoon, and even reduced-sodium versions are extremely salty.


● SOYA FLOUR The ingredients label should only list ground whole soya beans, says Cameron Wells, a dietitian at the Physicians Committee for Responsible Medicine in the US.