Kombucha, sauerkraut, kimchi or kefir… many fermented foods are being lauded for their gut-friendly bacteria. Dietitian Katrina Pace looks at the science behind the claims.
Fermented foods have been health-food buzzwords for a good while now, and people are even learning to make their own. They’re taking to social media and attending weekend workshops to talk about bubbling pots, cabbage smells, second ferments and how to stop mould growing. Kitchens have suddenly turned into chemistry labs!
Now, with fermented foods breaking free from health food stores and landing in your local supermarket, they’ve turned mainstream. So, what are they, and what’s the hype about?
The old now becomes new
Originally, fermenting food was a way to preserve produce from harvest time through the cold days of winter. But even more than that, fermented foods were thought to have unique health properties.
Almost every culture in the world has its own traditional fermented foods, but not all are health foods. Common foods that you may know well, without realising that they’ve been fermented, include chocolate, cheeses, salami, tea and yoghurt.
Food can be fermented by adding bacteria or yeasts (cultured ferments), or by creating an environment that enables bacteria to grow and ferment naturally on the food (wild ferments).
Pickled vegetables were fermented by adding bacteria and salt rather than vinegar, which is often used today. The traditional fermented porridge of Scotland and Ireland has winged its way back to popularity as ‘overnight oats’. Fermented bean products, such as douchi from China, tempeh from Indonesia, or miso and natto from Japan, are often seen in supermarkets and Asian grocers.
Your tummy’s best friend
Today’s interest in fermented foods is less to do with food preservation and more to do with the major health benefits associated with them.
Fermentation increases the bacteria in the foods (which is why they are called probiotic foods). Regularly consuming fermented foods is like taking probiotic capsules — we can influence good bacteria that grow in our digestive system.
Fermentation also helps us to pre-digest the food, which means it is often also easier for us to digest, and converts vitamins and minerals into a form that is easier for the body to put to good use.
Vitamins A, B, C and K also increase during the overall fermentation process. Other key benefits of fermentation include reducing inflammation and positively influencing the body’s metabolism.
Health claims: Fact or fiction?
Fermented foods ease tummy bloating
Tummy troubles including gas, bloating, cramps, irritable bowel syndrome, diarrhoea and even constipation may be due to the bacteria growing in your gut.
The bacteria in fermented foods can withstand the acid in your stomach and, along with natural fibres, are transported through the whole digestive system.
Studies show fermented foods can change bacteria that grow in your gut, reduce ‘bad’ bacteria and counteract tummy troubles. Find it hard to digest cabbage? Don’t worry: fermentation makes cabbage easier to digest, so even the most sensitive tummies can usually manage it.
A 2014 study indicated that people who are suffering from chronic constipation might benefit from taking 500ml per day of milk kefir. In the study, stool frequency was significantly increased, stool consistency was improved, and laxative consumption was decreased.
Fermented foods can cure diabetes
Nothing can ‘cure’ diabetes, but there are indications that regularly eating fermented foods helps control blood-glucose levels.
Researchers have found that the changes in gut bacteria that happen with diabetes can affect the way in which your body harvests energy — contributing to obesity — and can encourage inflammation.
Research on animals has shown that drinking kombucha regularly can change enzyme activity, reducing blood glucose spikes after meals. It does this by decreasing the amount of glucose that is absorbed during digestion.
Kombucha is high in antioxidants, polyphenols and organic acids, all of which affect digestion. But be careful, as store-bought kombucha can be much higher in non-fermented sugar than homemade.
Milk kefir, taken over the long term, has been shown to improve glucose tolerance and decrease blood-glucose levels. It can be used alongside diet and medication to reduce high blood glucose in people with both types 1 and 2 diabetes.
Fermented foods improve your mood
A change in gut bacteria has been observed in some people with irritable bowel syndrome and seems to be linked to depression and anxiety.
Both human and animal studies have shown that taking certain bacteria can improve feelings of well-being and reduce anxiety. The main bacteria found in sauerkraut are Lactobacilli plantarum, which produce neurotransmitters that may help to reduce feelings of depression.
Gut bacteria make neurotransmitters, such as dopamine and seratonin, which regulate mood.
Many chronic inflammatory disorders have also been linked to a highly processed Western diet, which changes gut bacteria growth.
Fermented foods prevent food allergies
A link exists between the various types and range of bacteria in your gut and risk of developing allergies.
Several lactic acid bacteria found in kefir have been associated with helping change gut bacteria so that they in turn can help prevent allergy. How do they do it? Bacteria can change the immune signals sent out by the body. These studies suggest that consistent use of kefir could help relieve allergy symptoms. Remember, cow’s milk in any form is not suitable for children under one year old.
Fermented foods help you lose weight
In Korea, it is thought that eating kimchi can help fight obesity. The cabbage used to make kimchi is usually fermented with daikon, radish, ginger and garlic. Given the changes it makes to gut bacteria, it seems possible kimchi might play a role in weight loss.
Several studies that involve obese Korean women have reported changes in gut bacteria that are related to weight loss. The bacteria found in kimchi change gut bacteria to favour those common in lean people. Regularly eating kimchi seems to alter gut bacteria and change how the body harvests energy, which may support weight loss.
The top three fermented foods
Want to help feed your gut? You can make kefir, kombucha, sauerkraut and kimchi easily and cheaply at home or find them in health food stores or supermarkets.
Kefir is a traditional fermented milk drink, similar to yoghurt. The milk — fermented by yeast and clusters of bacteria for about 24 hours — is slightly sour and fizzy and virtually lactose free. Twenty or more strains of beneficial bacteria and yeast have been identified from milk kefir.
Kombucha, made by fermenting black tea and sugar together using bacteria and yeast, has major anti-microbial and antioxidant properties. These have been shown to reduce diabetes risk, treat gastric ulcers and to bring down cholesterol in animal studies.
Kimchi and sauerkraut
For the best bacteria, you can’t beat these fermented cabbage cousins from Korea and Germany. Bacteria that hide in the folds of cabbage leaves convert natural sugars to lactic acid. The Lactobacillus plantarum in these foods are ‘good bacteria’ superstars.