Updated June 2026 · Ireland Health Shop · Expert input: Pat Coffey, Naturopath (UCC 2005)
The human gut microbiome — the collective ecosystem of bacteria, viruses, fungi, and other microorganisms that inhabit your gastrointestinal tract — has been described as a "virtual organ" in its own right. It influences digestion, immunity, metabolism, hormone production, mood, and even brain function through the gut-brain axis.
A healthy gut microbiome is characterised by diversity — a wide variety of species living in balance. Modern life has a profound negative impact on this diversity: antibiotic use, processed and low-fibre diets, stress, caesarean birth, bottle feeding, over-sanitisation, and lack of exposure to soil and nature all reduce microbial richness. Ireland scores poorly on many of these factors — antibiotic prescribing rates in Irish primary care are among the highest in Europe, processed food consumption is high, and the modern Irish lifestyle offers limited microbial exposure.
The World Health Organization defines probiotics as "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host." This is a precise definition — not every product claiming probiotic effects actually qualifies. True probiotics:
One of the most extensively studied strains. Lactobacillus acidophilus colonises the small intestine and vaginal epithelium. It produces lactic acid, hydrogen peroxide, and bacteriocins that inhibit pathogenic bacteria. Well-supported evidence for: preventing antibiotic-associated diarrhoea, managing IBS symptoms, reducing vaginal infections (including Candida and bacterial vaginosis), and reducing lactose intolerance symptoms.
LGG is one of the most researched probiotic strains in the world, with over 1,000 clinical studies. Particular strengths include: preventing and treating antibiotic-associated diarrhoea, reducing the duration of acute gastroenteritis in children (by approximately one day), and preventing atopic eczema in infants when taken during pregnancy and early infancy. It has exceptional stability — it survives stomach acid well.
Bifidobacteria dominate the infant gut and are among the first colonisers after birth. They ferment dietary fibre and produce short-chain fatty acids (SCFAs) that nourish the gut lining. B. longum has evidence for: reducing anxiety and stress (the gut-brain axis connection), managing IBS, supporting immune function, and reducing the duration of respiratory infections.
B. lactis strains have strong evidence for: improving bowel transit time (constipation), enhancing immune responses (particularly NK cell activity), and reducing bloating. Widely used in children's and elderly probiotics.
A particularly robust strain that survives well in fermented foods and the gut environment. Evidence for: IBS symptom reduction (including bloating and abdominal pain), reducing intestinal permeability ("leaky gut"), and anti-inflammatory effects in the colon.
Uniquely, this is a yeast rather than a bacterium — which means antibiotics don't affect it. S. boulardii is the best-evidenced intervention for: preventing antibiotic-associated diarrhoea and Clostridioides difficile (C. diff) infection, managing traveller's diarrhoea, and reducing Crohn's disease activity. If you're taking antibiotics, S. boulardii can be taken simultaneously without the 2-hour gap required for bacterial probiotics.
Produced in the gut naturally at low levels. Has evidence for: infant colic (a well-replicated finding), reducing H. pylori in the stomach (alongside standard treatment), cardiovascular health (reducing LDL cholesterol and blood pressure), and bone density. One of the more surprising multi-system strains.
Irritable bowel syndrome affects an estimated 10–15% of Irish adults — approximately 500,000 people. It's particularly prevalent among Irish women. While not life-threatening, IBS significantly impairs quality of life. Probiotics are one of the best-supported natural interventions for IBS, with multiple systematic reviews finding significant reductions in abdominal pain, bloating, and altered bowel habit. The strongest evidence is for multi-strain products containing Lactobacillus and Bifidobacterium species, with 4–8 weeks of use needed to assess response.
Ireland has among the highest rates of antibiotic prescribing in the EU. Every course of antibiotics disrupts the gut microbiome — some studies suggest significant diversity loss that can take 6–12 months to partially recover without intervention. Taking probiotics during and after antibiotic use (using S. boulardii during, and bacterial probiotics 2 hours after each dose) significantly reduces antibiotic-associated diarrhoea and helps restore microbiome diversity.
Approximately 70% of the immune system is located in and around the gut — the gut-associated lymphoid tissue (GALT). Probiotics modulate immune responses by interacting with dendritic cells and regulatory T cells. Several trials have found that probiotics reduce the incidence and duration of upper respiratory tract infections — particularly relevant in Irish schools and workplaces during the autumn/winter season.
The gut and brain are in constant bidirectional communication via the vagus nerve, the enteric nervous system, and circulating cytokines and hormones. The gut microbiome produces or influences around 90% of the body's serotonin (a neurotransmitter crucial to mood), as well as GABA, dopamine precursors, and short-chain fatty acids that affect brain function. Research on "psychobiotics" — probiotics specifically selected for mental health effects — is one of the most exciting areas in current science. Early clinical trials suggest benefits for anxiety, stress, and mild depression.
Before refrigeration, fermentation was Ireland's primary food preservation method. Traditional Irish fermented foods include:
Fermented foods are an excellent complement to probiotic supplements — but for therapeutic purposes (IBS, post-antibiotics, immune support), a quality supplement with specific, well-evidenced strains at adequate doses is more reliable than food alone.
Probiotics work best when they have something to eat. Prebiotics are non-digestible food components (primarily certain fibres) that selectively feed beneficial bacteria. Key prebiotics include inulin, FOS (fructooligosaccharides), GOS (galactooligosaccharides), and resistant starch.
Good prebiotic food sources in the Irish diet: onions, leeks, garlic, Jerusalem artichokes, green bananas, oats, and cooked-and-cooled potatoes (the cooling process increases resistant starch content). If your probiotic supplement contains prebiotic fibres (often labelled as "synbiotic"), this is a bonus.
With hundreds of products available in Irish health stores and pharmacies, choosing can be overwhelming. Key criteria: