Your guide to probiotics

Everything you need to know about probiotics, from the potential health benefits to the signs that your gut bacteria is out of balance.

🕒 9 min read

What are probiotics?

The term 'probiotics' describes the use of live 'friendly' bacteria and occasionally yeasts, for their positive effects on health. The most commonly used probiotics are those that produce lactic acid, such as Lactobacilli and Bifidobacteria. These bacteria are acid tolerant, so a significant number survive passage through the stomach to reach and colonise the large intestines, where they have beneficial effects on digestion and immunity.

What are the benefits of probiotics?

So called 'good' or probiotic bacteria play an important role in maintaining intestinal health. They produce lactic and acetic acids as well as natural antibiotics which discourage the growth of the less beneficial bacteria that produce gases and may contribute to symptoms such as flatulence, bloating, pain and diarrhoea.

Another benefit of probiotic bacteria is that they produce short-chain fatty acids, which act as a major energy source for intestinal lining cells. These short-chain fatty acids are also absorbed from the colon and transported to the liver, where they have helpful effects on cholesterol metabolism.

The gut-brain axis is another area of interest. Bowel bacteria secrete substances that have indirect effects on the brain, so your microbiome may play a role how you cope with stress and anxiety. Serotonin, for example, is best known as a brain transmitter that regulates mood, but as much as 90 per cent of your body's serotonin is actually made by cells lining the digestive tract – and the right balance of gut bacteria is thought to be important for stimulating its production.

In addition, serotonin helps your brain to filter out all the sensations involved with moving solid wastes through the gut, so you aren't aware of them. If the microbiome becomes disrupted, then changes in serotonin secretion may mean these sensations are brought to the fore and increased sensitivity of stretch receptors may trigger the discomfort felt by people with irritable bowel syndrome (IBS). This is why probiotics for IBS might be worth considering.

When all this is put together it's clear that if your microbiome loses its bacterial diversity, or becomes dominated by one type of bacteria, your health may suffer.

Knowing your gut bacteria

How it all begins

While in the womb, our bowel remains sterile but after birth it quickly becomes colonised by bacteria encountered in the birth canal, within the environment and, after weaning, on our food.

By adulthood, our large bowel contains an estimated 3.8 x 10¹³ (trillion) bacteria. Together with the fungi and other microorganisms present, this community of living microbes is known as the microbiota (or less specifically as the microflora).

Living in harmony?

A term that's used more often than 'microbiota', is 'microbiome', which consists of the microbiota plus other microbial products (e.g. proteins, nucleic acids, genes, toxins and signalling molecules) present within a well-defined 'theatre of activity', such as the human gut.

The microbiome contains over 1,000 different bacterial species which, together, are estimated to have 150 times more genes than the human genome. These gut bacteria produce hormones; in fact, the microbiome is considered to act like an endocrine organ that can influence our mood, energy metabolism and insulin resistance.

As a result, our gut bacteria may have significant impact on glucose control, cholesterol levels, obesity, sleep, energy levels and fatigue in ways that are not yet fully understood.

How to keep your gut bacteria in balance

Your bowel is designed to empty regularly, which means you lose beneficial probiotic bacteria every day, alongside their less desirable relatives. Normally, these 'good' bacteria are replenished by the multiplication of bacteria that adhere to your gut wall and those that live within your appendix (if you still have one) providing you're giving them what they need.

Prebiotic fibre

The type of diet you eat has a profound effect on your bowel bacterial balance, as different species of bacteria thrive on different types of carbohydrate, fibre and protein.

Some forms of fibre selectively stimulate the growth of friendly digestive bacteria in the bowel. Known as prebiotic fibre (e.g. fructo-oligosaccharides, inulin), these cannot be broken down and absorbed by less desirable gas-forming bowel bacteria, but can be used as a food source by our immune-stimulating, lactic acid producing bacteria. Prebiotic foods include onions, leeks, asparagus, garlic.

Globe artichoke, for example, has numerous beneficial effects on digestion and is a source of inulin, a prebiotic fibre that stimulates the growth of beneficial digestive bacteria. Fructo-oligosaccharide and inulin supplements are also available.

A Mediterranean diet

Emerging research suggests that following a Mediterranean style diet, which provides lots of vegetables, fish and olive oil, can increase levels of probiotic bacteria in the gut by almost 10 per cent compared with a meat-rich Western style diet. Lifestyle factors, such as alcohol and smoking, can impact your bowel bacterial balance, too.

Probiotics

Live 'good' bacteria are naturally found in fermented foods such as kimchi, sauerkraut, kefir, kombucha, sourdough, miso, tempeh and some yoghurt, so eating these helps to shape your microbiome. However, as many of these foods can have quite strong flavours that you may not be too keen on, or able to eat on a regular basis, taking a daily supplement is an easier way to obtain the benefits.

And in the future...

Researchers predict that within five years, doctors will assess your microbiome and prescribe drug treatments and doses based on your gut type, as a form of personalised medicine. The use of gut microbe transplants (known as a trans-poo-sion) may even become mainstream.

What happens when gut bacteria are out of balance?

An imbalance in the digestive bacteria in the gut is known as dysbiosis. Gut dysbiosis can also cause a number of digestive symptoms, including bloating, flatulence and diarrhoea (this may also explain why diarrhoea is the most common gut side effect and affects between 5 per cent and 35 per cent of people taking antibiotics). It's also associated with long-term intestinal problems such as diverticular disease, irritable bowel syndrome and inflammatory bowel disease.

Signs and symptoms of dysbiosis

Although the early symptoms of dysbiosis mainly affect the bowel, others include fatigue, joint pain, poor concentration, anxiety and even depression. Different people will experience different symptoms, based partly on the balance of bacteria present in their bowel, and the way these interact with the genes you have inherited.

While the symptoms of dysbiosis may be compatible with irritable bowel syndrome, this is not a diagnosis you should make yourself. Always seek medical advice if you experience a change in bowel habit – especially if you also notice other red flag symptoms such as unexpected weight loss or blood in the stools (these can be a sign of bowel cancer which, when diagnosed early, is more easily treated).

Latest research suggests that gut dysbiosis also increases the risk of health problems affecting other parts of the body, including asthma and allergies, diabetes and arthritis. This is because gut bacteria help to prime the immune system. In short, it seems that just about any persistent physical or psychological symptom could be related to dysbiosis.