I get asked a lot whether or not soybeans and soy products, such as tofu and tempeh, are good for you. And it’s easy to see why there’s so much confusion on this topic, as many of the headline messages we see in the media are very conflicting. Some hail tofu as some kind of super-food, while after reading others you might expect to grow a third eye. So, I thought I would bring you the best quality and most up-to-date scientific evidence on the health topics surrounding soy.
Soy and hormones in men
The top concern I hear about from men is whether soy can affect male hormone levels. There have in the past been concerns about oestrogen-like activities of the isoflavones found in soy decreasing testosterone levels in men. However, the basis of these claims stems from early studies in rodents. And it’s been shown that rodents metabolise isoflavones very differently to humans. In fact, a recent meta-analysis – one of the best form of scientific evidence – combined the results from 15 human clinical trials, and concluded that soy foods do not alter testosterone levels in men (ref). Even at higher than average rates of consumption (higher than is even typical among some Asian cultures), there is also no evidence that soy isoflavones affect circulating oestrogen levels in men (ref). This does all kind of make sense… the hundreds of millions of men in Asian cultures who frequently eat soy products are not infertile or growing ‘man boobs’. In fact, there is reason to believe that soy is one of the reasons why the Japanese, among the biggest soy eating countries in the world, is also one of the healthiest nations. This brings me on to the health benefits of soy:
Soy is an excellent source of protein
Soybeans are a complete protein, meaning they provide all the essential amino acids (the ones we have to get from our food because we can’t make them in our body). A cup of cooked soy beans contains a whopping 22g protein, a 150g serving of tempeh has 28g, and a 150g serving of tofu contains 19g. This means for anyone looking to increase their protein intake, which can help with short-term weight loss or gaining muscle and strength, soy products can be an extremely useful addition to the diet.
Soy can replace foods that are bad for you
As mentioned, soy provides an excellent source of protein, and all without the cholesterol and saturated fat levels found in most meat products. So if you swap a pork sausage hot dog for a soy-based alternative, you are avoiding processed meat, which is bad for our health in a number of ways. If you’re replacing it with a high protein, low fat, high vitamin and mineral based food like tofu, there are significant advantages for your health.
Soy could be protective against cancer
This has been a topic of debate in the past, again because of early studies in rats who metabolise phyto-oestrogens differently to humans. But recent meta-analyses, which combine the results of numerous clinical trials in humans, show that soy consumption could in fact be associated with reduced risk of breast cancer incidence (ref) and prostate cancer (ref). These effects have been shown to be both through direct mehanims, and through the ‘displacement’ of red and processed meats (as mentioned above). That’s equally as important because red and processed meats have been classified by the World Health Organisation as carcinogens (cancer causing) (ref).
Soy can decrease risk of heart disease and stroke
Soy products can reduce our risk of heart disease and stroke, because they reduce our blood cholesterol levels (ref). It does this in two ways: firstly, by directly reducing our liver’s cholesterol output. Secondly, again through the ‘displacement’ theory - soy products like tofu are often eaten as a replacement in our meals for meat products, which are much higher in saturated fat. By replacing meat with tofu or tempeh, the saturated fat content of the meal is significantly reduced, which is why soy consumption is associated with lower risk of heart disease and stroke (ref).
Soy can improve bone health
Increased consumption of soy foods is associated with improved markers of bone health and lower risk of osteoporosis and bone fractures, especially in post-menopausal women (ref). More research is needed here but the evidence so far is very promising! (ref)
The downsides of soy products
Soy products that have been processed to resemble the taste of a bacon rasher or turkey slice require quite a bit of processing, and the ingredients list can look worryingly long. There is often added salt and fat in anything that has been battered, and other flavourings and colourings in mock-meat style products to give it a ‘meaty’ flavour. As with any foods, generally the less processing the better. For this reason, simple tofu is much better than the heavily processed imitation meats. Better still, tempeh which is made by simply fermenting cooked soybeans, is even less processed than tofu, and contains more protein too.
The take home message
The reason some people worry about soy foods is mainly because of early studies conducted in rats that used especially high levels of phyto-oestrogens. As mentioned before, rats metabolise the phyto-oestrogens in soy very differently to humans, and there’s a large (and growing) body of evidence showing the significant health benefits of soy products in humans. Want to incorporate soy into your diet more? Try my crispy sesame-coated baked tofu, incredible tofu quiche, or make a tofu ‘bacon’ BLT.