Intuitively, many have sensed that we are what we eat and that we fuel our bodies by the gut, but it’s only recently that scientists have recognised the critical role of the intestinal microbiome.
“These are organisms that live within the gut that we now know regulate the function of various processes within the body, affecting everything from the health of our skin and joints to our heart, brain, and kidneys,” says Aoibhlinn O’Toole, a consultant gastroenterologist at Dublin’s Beaumont Hospital and a clinical associate professor at Royal College of Surgeons in Ireland.
Our gut and brain are interconnected, sending signals back and forth that affect how we feel, think, and function, says Orlaith Kelly, a consultant gastroenterologist at Dublin’s Connolly Hospital: “The neurons of the gut communicate with the neurons of the brain through the central nervous system, particularly the vagus nerve.
“The gut and brain are also connected through chemicals called neurotransmitters. Serotonin is one example. It affects mood and brain function and was once thought only to be produced in the brain, but we now know that up to 90% of it is synthesised in the gut.”
Alan Desmond finds it hard to believe that the gut was once seen as a tube for processing food. Originally from Cork, the lead gastroenterologist at the Devon Gut Clinic in Britain and the author of argues that gut health is as vital as brain health.
“The gut is home to trillions of microbes and its own nervous system, which talks to your brain 24/7,” he says. “When your gut is happy, it supports digestion, immunity, energy, mood, and sleep. When it’s unhappy, you feel it in every part of your life.”
If you are someone who regularly suffers from ailments like heartburn, acid reflux, constipation, bloating, or diarrhoea, you’re not alone. A 2021 study of 73,000 people in 33 countries found that 40% of adults struggle with these so-called functional gastrointestinal disorders.
“These symptoms are at the lower end of the severity scale, but they still cause people to restrict their diets, movements, and lifestyles, and impact their quality of life,” says Kelly.
Further up the severity scale is irritable bowel syndrome, which HSE says causes symptoms like stomach cramps, bloating, diarrhoea, and constipation, and can last for days, weeks, or months at a time.
“As a gastroenterologist, I tend to see people with the most severe problems,” says Kelly. “These include people with inflammatory bowel disease such as Crohn’s and ulcerative colitis, people with coeliac disease and people with gastrointestinal cancers. Worryingly, we’re seeing a trend for more young people under the age of 45 being diagnosed with these cancers.”
Dr Alan Desmond. the lead gastroenterologist at the Devon Gut Clinic in Britain
Desmond is adamant that modern lifestyles deserve some portion of the blame, citing physical inactivity and diets built around meat, unhealthy fats, and ultra-processed foods as the main culprits.
“Our gut microbiome thrives on fibre, which comes from a diversity of plants,” he says. “But many diets are high in red and processed meats, refined carbohydrates, and sugar, all of which starve the good bacteria in our gut and feed the bad ones.”
Ongoing stress can also undermine our gut health.
“Our bodies follow cycles,” says Kelly. “We have a sleep cycle, a menstrual cycle and a digestive cycle. But if we lead busy and stressful lives, we may not eat at set times, and our gut can get out of kilter. Sitting down to eat at regular times can make a big difference to our gut.”
Certain recreational habits also play a role, says O’Toole: “Smoking and vaping affect the gut, and so does overconsumption of alcohol.”
Frequent antibiotic use can upset the gut’s microbiome, she says: “And a lack of exercise can slow its motility. If you’re active, your gut will be active too.”
Desmond recommends starting with diet, describing it as “the number one driver of gut health”. His advice to his clients is that the more plants they eat — including fruits and vegetables, wholegrains, beans, lentils, nuts, and seeds — the more diverse and resilient their gut microbiome will be.
He suggests starting by swapping red and processed meats for plant proteins like beans, lentils, tofu, and tempeh; choosing wholegrains over white bread, white pasta, and white rice; and always trying to fill half their plate with colourful fruits and vegetables.
“Having a variety of plants at the heart of every meal allows you to feed yourself and your gut microbiome at the same time, and both will thank you,” he says. “You’ll lower your risk of bowel cancer, heart disease, and diabetes, while boosting your energy, mood, and digestion.”
For people who struggle to overhaul their diets in this way, O’Toole encourages them to follow the 80:20 rule: “Aiming to eat whole foods and avoid processed and ultra-processed foods 80% of the time can make a real difference to gut health.”
She would also like people to learn how to read food labels so that they can recognise ultra-processed foods: “The more ingredients there are in a food, the more likely it is to be processed. I tell my patients that if they are going to buy bread or pizza dough or frozen chips in the supermarket, they should choose the product with the fewest ingredients and the least additives, synthetic sugars, preservatives, and oils.”
Watch out for misleading packaging, she says, citing protein bars marketed as health foods as an example: “Look at the ingredients and you’ll see that many of them are just glorified candy bars.”
Dr Aoibhlinn O’Toole, a consultant gastroenterologist at Dublin’s Beaumont Hospital and a clinical associate professor at Royal College of Surgeons in Ireland.
O’Toole advises her clients, particularly those with inflammatory bowel disease, to steer clear of carrageenan and methyl cellulose.
“Carrageenan is an emulsifier and methyl cellulose is an artificial additive, and both have been shown to cause inflammation in the gut,” she says. “They are added to lots of ready-made meals and sauces, so look out for them on food labels.”
Cured meats like bacon, sausages, salami, and chorizo should come with a health warning, says Kelly.
“The World Health Organisation classified them as carcinogens in 2015. This means they cause cancer, so it’s best to limit our intake of these meats,” she says.
Surprisingly, she urges people who experience regular gut issues to pay attention to their fruit consumption. “Fruit can be an issue as the high levels of fructose sugar it contains can cause bowel discomfort for some”.
Fibre is the fuel our gut bacteria thrive upon, says Desmond. It keeps our gut moving, supports a healthy microbiome and produces compounds that protect our gut lining and reduce inflammation.
The trouble is that many of us don’t eat enough of it. In 2018, the Irish Nutrition and Dietetic Institute reported that 80% of Irish adults did not meet the recommended daily intake of 25g to 30g.
“This is a big reason why many have issues with gut function,” says Kelly.
The solution is straightforward — adding foods that are rich in fibre, such as fruit, vegetables and wholefoods to every meal.
“It’s not always easy, but it’s worth bearing it in mind as an aim,” says O’Toole.
“Regular activity will keep your gut active and help you to maintain a healthy weight, which is important too,” says O’Toole, who recommends a combination of cardio and core-strengthening exercises.
She also emphasises the importance of quitting smoking and vaping and keeping alcohol consumption within the recommended limits.
“Maintaining regular meal patterns by eating at set times and taking enough time to eat,” helps too, says Kelly.
“And don’t forget to make enough time for sleep and activities that reduce stress,” adds Desmond.
Finally, if your gut is still telling you that something is wrong, seek help from a doctor.
“There are specific conditions that require specific dietary modifications and even medication,” says Kelly.
“When someone has a specific problem, a gastroenterologist has to look at that problem and adapt their advice accordingly.
“So, if you have gut issues and no lifestyle changes seem to be helping, make an appointment to see your doctor.
“They will be able to diagnose what’s wrong and recommend the most suitable course of treatment.”
Dr Orlaith Kelly, a consultant gastroenterologist at Dublin’s Connolly Hospital
Is there a specific food or food group that we can consume more of to improve our gut health? We put this question to our three gastroenterologists.
Dr Aoibhlinn O’Toole says it’s wholefoods. These are minimally processed natural foods, including unrefined carbohydrates such as oats and rice, fruits and vegetables, beans, lentils, nuts, seeds, and unprocessed meats and fish.
“If you’re unsure, look to the Mediterranean diet rather than the traditional Western diet,” she says.
Dr Alan Desmond recommends plants. “They feed beneficial gut bacteria, reduce inflammation, and help protect against disease,” he says. “The next time you’re making a shepherd’s pie, try making it with lentils and beans instead of beef or lamb. The lentils and beans deliver protein plus fibre and are also richer in vitamins, minerals, antioxidants, and phytonutrients that nourish your gut microbes while avoiding the saturated fat and harmful compounds found in red meat. They are much more gut-friendly.”
Dr Orlaith Kelly makes a particular case for kiwis. “I often recommend that people take them because of their high fibre content and low glycaemic index, which means they are a fruit that is relatively low in sugar,” she says.
“They also contain lots of vitamin C and an enzyme called actinidin, which helps digestion by breaking down protein.”
Research supports the claim that kiwis are beneficial for our gut health. In 2022, scientists from Japan, New Zealand, and Italy showed that eating two kiwis per day for four weeks helped people have more complete bowel movements, improving constipation, and abdominal discomfort. Another study from 2023 found that people who ate more kiwis had a decreased risk of colorectal cancer.
