Fermented foods have been in our diet for thousands of years. Beer and wine are classic examples of fermented foods where yeast converts sugars to alcohol. Other types of fermented foods use bacteria, such as Lactobacillus, to make foods like yoghurt, sauerkraut, kimchi and many others. And when you start talking about bacteria, you move into the realm of probiotics which come with a long list of health claims.
Probiotics and health
A probiotic is any live micro-organism which when consumed in adequate amounts, offers some form of a health beneﬁt. The clinical evidence for probiotics places treatment of diarrhoea (especially caused antibiotics) at the top of the list. A potential benefit in treating irritable bowel syndrome looks likely too. After this, inflammatory bowel disease, prevention of certain infant allergies such as atopic dermatitis, and an overall general protection against infection deserves considering, but the science is still evolving.
Novel areas of research are now even looking at direct links between gut bacteria and obesity and metabolic disorders such as diabetes. And now appearing on the horizon is some evidence to link gut bacteria with mood and behaviour – called psychobiotics – something we will likely hear more of in the future.
Probiotic foods: more than just dairy
Any mention of probiotics immediately brings foods such as yoghurt and popular dairy based drinks like Yakult to mind. In much of the Western world, dairy get most of the attention for its probiotic benefit, but there are many other probiotic foods now being re-discovered.
Two well-known fermented foods with strong cultural ties are the German staple of sauerkraut and the traditional Korean dish of kimchi. Both these cabbage-based dishes are made by lactic acid bacteria fermentation. The main differences between them is sauerkraut is cut much finer and has no other ingredients apart from brine, while kimchi is cut into larger pieces and served with a variety of condiments such as chilli, garlic, pepper and fish sauce.
So how healthy is sauerkraut and kimchi? Cabbage itself is naturally high in fibre and contains isothiocyanate compounds, which have cancer-fighting properties. And as long as you choose unpasteurised sauerkraut, you will gain a potential probiotic benefit.
Several studies have found that kimchi may be a potent food in lowering cholesterol and controlling blood glucose. A just published study involving 100 volunteers who followed a low or high kimchi diet for 7 days in a controlled housing dormitory found dose effects of kimchi on fasting blood glucose, total glucose, total cholesterol and LDL-cholesterol.
Kefir is an interesting probiotic food as on the surface appears similar to yoghurt. Kefir can be made from milk from any ruminant animal, but is fermented with a different variety of bacteria and uses a starter culture that also contains yeast. A 2013 review on the health benefits of regular kefir consumption found good evidence for its antimicrobial activity, improved gut health, anti-carcinogenic activity, control of blood glucose and cholesterol, improved lactose digestion and a stronger immune system. Quite an impressive list indeed.
Another popular non-dairy probiotic food is the Japanese staple of natto, which forms the base of miso soup and many other foods. It is made by the fermentation of soybeans with the bacterium Bacillus subtillis. Natto offers some of the health benefits similar to soy foods, but with additional value coming from its probiotic properties. Interestingly, natto contains the enzyme nattokinase which may reduce blood clotting risk in thrombosis as it can degrade fibrin.
Moving out of the realm of solid science, we have an emerging ‘star’ on the fermented food stage, that being kombucha. With origins in China, kombucha is made from a sweet tea base that has been fermented with a symbiotic colony of bacteria and yeast. Popular in the health food, juice and detox scene, it is sometimes called ‘mushroom tea’ – getting its name from the brown slimy crust that forms on the surface of the beverage.
Claimed to be a super health elixir with a long list of health benefits, kombucha is one drink where science has yet to catch up. So far no clinical trials have been published in humans. Considering its boutique price premium, unless you plan to make your own, I would be looking elsewhere for my probiotic hit.
While the long list of health claims from eating fermented looks impressive, the evidence for some of them is certainly trailing. People have been eating fermented foods for thousands of years and they certainly have a role to play in any diet. Fermented foods are not a silver health bullet, but when added to a healthy diet, have the potential to make it even healthier.
Confused about the mixed soup of nutrition messages being stirred through the media? Tim maintains an active nutrition blog at www.thinkingnutrition.com.au where you'll find the latest nutrition research and controversies discussed in straight forward language, distilling out what you need to know for your better health.