By Lisa Jamieson

As a newly-qualified pharmacist in the mid-1990s, armed with my first edition copy of Symptoms in the Pharmacy, I worked in community pharmacy selling a range of OTC medicines for gastrointestinal conditions. I completed a gastroenterology module during my clinical pharmacy MSc and read NICE guidance on topics like dyspepsia and irritable bowel syndrome. As a GP practice-based primary care pharmacist, I took a lead on gastroenterology in my team, and thought I had a good grasp of how gastrointestinal conditions should be managed. 

Then in 2011, when I completed the 'gut, allergy and food intolerance’ module for my nutritional medicine MSc, everything I thought I understood about gut health came crashing down around me. Learning about the gut microbiota, and how and why it is so essential to maintain good health, resulted in a complete paradigm shift in my thinking. 

Collectively, the microbes living within us have so many essential functions, they are considered to be as vital as one of our organs. The ‘forgotten organ’ that is the gut microbiota is made up of 1-2 kg of microorganisms, including bacteria, viruses, yeasts, protozoa and archaea. Microbes are found all the way through the gut, in increasing quantities, with the highest concentration in the large intestine. 

Core functions of gut microbes

Humans have evolved to live in harmony with our gut microbes. The range and number of species living within us are influenced by whether we are born by caesarean section or delivered vaginally, our lifestyle, and especially the food we eat. The important jobs they do can be grouped into three core functions: 

Extra nutrition (metabolic functions) Gut microorganisms help with fermentation of non-digestible substances and increase the harvest of energy from our food. They help to produce some nutrients, including vitamin K and some B vitamins, and assist with absorption of other vitamins and minerals. They also help to stimulate gut peristalsis and improve our tolerance to lactose.

Protection against pathogens Different species of microorganisms live together creating biofilms, which protect the lining of the gut wall. Our friendly microbes compete against, and displace, invading pathogens. They are also capable of producing antimicrobial factors such as lactic acid, hydrogen peroxide and bacteriocins. This improves gut barrier function and helps protect us from infection.

Strengthening the immune system The constant activity of the gut microbiota results in stimulation of the immune system, which improves its readiness to combat pathogens. The mixture of species living within us influences how the immune system develops, including the dampening of inflammation and suppression of hypersensitivity, for example food allergy. 

Killing off countless microbes with unnecessary antibiotic use can damage the gut microbiota, which can have far reaching health consequences. We need to look beyond antimicrobial resistance to the protection of our gut microbiota, as a major reason for reducing or limiting our use of antibiotics as part of antimicrobial stewardship. 

Dysbiosis is when the gut microbiota is imbalanced. It can lead to inflammation and can contribute to mental health problems, such as depression and anxiety. Dysbiosis is also associated with autoimmunity.

Small intestinal bacterial overgrowth (SIBO), which results in too many fermenting microbes in the small intestine, can correlate with irritable bowel syndrome, coeliac disease, and Crohn’s disease. SIBO can lead to malabsorption of nutrients, resulting in malnutrition. Symptoms overlap with dyspepsia. If SIBO is undiagnosed or misdiagnosed, this can cause further problems, because medicines such as proton pump inhibitors can also cause malabsorption of some nutrients and worsen SIBO. 

The range of gastrointestinal symptoms from a malfunctioning microbiota is varied and includes gas production, bloating, belching, nausea/vomiting, constipation, diarrhoea, food intolerances, flatulence, foul-smelling stools, steatorrhoea, and pain. Symptoms can also extend beyond the gut due to the impact on the immune system, for example rashes, itching, inflammation and mental illness. Medicines may only temporarily treat the symptoms; they are unlikely to address the underlying cause. 

Answering the question, “can probiotics help?” is about as easy as answering “do drugs work?” It depends on what you are trying to treat and on which probiotic you are considering supplementing. There is emerging evidence that some probiotic supplements can help a range of conditions, from antibiotic-induced diarrhoea to irritable bowel syndrome. Furthermore, evidence is emerging that probiotics can impact on mental illness, e.g. anxiety and depression. 

Maintaining a healthy gut microbiota is important for keeping the whole body healthy, and a dietary approach is needed. Vegetables and fruits contain prebiotics, for example inulin, which is found in bananas, onions, garlic, chicory and artichokes. Prebiotics act as ‘food’ for the ‘friendly bacteria’. Therefore, eating more prebiotic-rich foods can have a big impact on the composition of the gut microbiota. 

If we want to get serious about improving health, tackling the prevention agenda, and deprescribing, we need to focus much more on nutrition and looking after our gut microbiota.

Further reading

Cartwright P. Probiotic Allies: How to Maximise the Health Benefits of Your Microflora. Publisher: Prentice Publishing (14 Mar 2011)

Anderson SC, Cryan JF, Dinan T. The Psychobiotic Revolution: Mood, Food, and the New Science of the Gut-Brain Connection. Publisher: National Geographic (30 Nov 2017)

Lisa Jamieson BPharm (Hons), MSc (Clin Pharm), MSc (Nutr Med), MRPharmS is a pharmacist and nutritionist