Everything we eat and drink— from probiotic yoghurt to donuts to a pork chop — has an effect on the microbes that live in our bodies, which, in turn, have an effect on our health.
The microbiome is made up of trillions of microbes, and these microbes need food. If you eat a lot of food that one strain of microbes need, that strain will thrive.
Awareness about the importance of good gut health has many people doing their very best to eat well. The rising popularity of live fermented probiotic foods, which contain strains of bacteria or fungi that have been shown to have a beneficial effect on health, have spawned the now mainstream availability of kombucha, kimchi, kefir and the like. There’s nothing wrong with these foods, of course, but are they doing what we think they are? Possibly, but there’s a more effective way.
There are two categories of microbes in our gut: those that live there permanently, and those that just pass through. The microbes in probiotic foods are generally visitors. While valuable for health they don’t, as a rule, become residents.
Resident microbes are acquired from birth through early childhood — with a few picked up here and there later in life. We pass microbes to each other and through generations. These gut microbes help with immunity and the nervous system, and while there are various strains, some can only live in the human gut. They’re specialised and exclusive to us, and we need to look after our residents first.
Despite the idea that the microbiome is set, it can change. Within the gut, these populations are dynamic, with lifespans as short as a few minutes. If something changes, such as the introduction of a new food, a lack of the microbes’ preferred fibre, or taking antibiotics, the microbiome changes. This effect is rapid – within 24 hours. The magnitude of the change is where the difference is made.
Our digestive system is highly acidic, which makes digestion easier but also helps to filter out or kill off foreign organisms. This ensures that it’s rare for the microbes we consume to survive digestion to then multiply in our system. Those that do survive stay a little while and our immune system then wards them off.
Taking probiotic foods or supplements is a good way to introduce visiting microbes, but they are unlikely to become resident. (They’re unlikely to do any harm, though, so if you like eating them then continue to do so.)
So, if probiotics are not the ideal foods for your resident microbiome, what is? Rather than focusing on trendy – and expensive – products, we instead need to focus on their food of choice: Fibre.
The fibre that our gut microbes love is the type that we can’t digest. It’s made up of long chains of carbohydrates that humans find very difficult to break down. Think of cattle eating grass and hay: they have four stomachs to digest the fibre it contains. When we eat, the fibre travels through the digestive system relatively unchanged, and when it reaches the lower intestine – where most of our gut bacteria reside – is when the magic starts.
Our gut bacteria make a meal of what we can’t digest. When this type of fibre encourages the growth and health of beneficial microbes, it’s known as prebiotic.
When we eat prebiotic foods, the gut bacteria rewards us by making metabolites that help fight inflammation, defend us from infection, and help to crowd out harmful bacteria. It also appears that they help maintain the health of the lining of our intestines, which protects against allergies and prevents small food particles entering the bloodstream.
So, instead of focusing on adding probiotics, think first about prebiotics. Where do you get this marvellous fibre? Primarily, it comes from vegetables, and mostly from raw vegetables. Eat your greens, add some onion and garlic, and eat those wonderful probiotic foods if you like them, and you’ll have a happy and healthy microbiome.