The gut microbiome has become one of the most intensively researched areas of medicine in the past two decades. What began as a niche area of gastroenterology has expanded into a field that now touches cardiovascular health, mental health, immune function, metabolic disease and — particularly relevant for your audience — IBS and digestive disorders.
The science is genuinely exciting, but it is also genuinely complex. This guide cuts through the noise to give you evidence-based, practical guidance on how diet affects your gut microbiome, what the research actually supports, and what you can eat — starting today — to support a healthier, more diverse gut ecosystem.
What Is the Gut Microbiome and Why Does It Matter
The human gut microbiome is the community of trillions of microorganisms — bacteria, viruses, fungi and other microbes — that live primarily in the large intestine. The bacterial component alone comprises somewhere between 500 and 1,000 different species, with a combined genetic content that dwarfs the human genome by a factor of approximately 150.
This microbial community performs functions that are essential to human health. It ferments dietary fibre into short-chain fatty acids — including butyrate, propionate and acetate — that provide energy for the cells lining the colon, regulate immune function and protect against inflammation. It synthesises certain B vitamins and vitamin K. It metabolises bile acids and plant compounds in ways that affect cholesterol levels and oestrogen metabolism. And it maintains the integrity of the gut lining — the barrier that separates the gut contents from the bloodstream.
When the microbiome is disrupted — a state called dysbiosis — these functions are compromised. Dysbiosis has been associated with IBS, inflammatory bowel disease, obesity, type 2 diabetes, depression, anxiety and a growing list of other conditions. The connection between gut microbiome health and systemic health is now considered one of the most significant frontiers in medicine.
The Diet-Microbiome Connection
The composition of your gut microbiome is influenced by genetics, age, medications, stress, exercise and environment — but diet is the single most powerful modifiable factor. Research consistently shows that dietary changes produce measurable shifts in microbiome composition within days to weeks.
The most comprehensive study of diet and the microbiome to date — the British Gut Project, based at King's College London — found that the single strongest predictor of microbiome diversity was the number of different plant foods consumed per week. People eating 30 or more different plant foods per week had significantly more diverse microbiomes than those eating 10 or fewer, regardless of whether they identified as vegan, vegetarian or omnivore.
Diversity matters because different bacterial species thrive on different substrates. A diverse diet feeds a diverse microbiome. A narrow diet narrows the microbiome — with downstream consequences for health.
What to Eat to Support Your Gut Microbiome
Eat as many different plants as possible each week. The 30 plants per week target from the British Gut Project is a useful benchmark. Herbs, spices, nuts, seeds, legumes, wholegrains, fruits and vegetables all count. A teaspoon of mixed seeds on your porridge, a handful of walnuts in your salad and fresh herbs on your dinner each add to your weekly total without requiring significant changes to how you eat.
Prioritise prebiotic foods. Prebiotics are substrates — primarily types of dietary fibre — that specifically feed beneficial gut bacteria. Foods rich in prebiotics include garlic and onion (high in fructans), Jerusalem artichoke, leeks, asparagus, bananas, oats, flaxseed, chicory root and apple. Note that many classic prebiotic foods are high FODMAP and will need to be managed carefully by people with IBS — a point addressed below.
Include fermented foods. Fermented foods contain live microorganisms that can temporarily colonise the gut and exert beneficial effects. A landmark study published in Cell in 2021 found that a diet high in fermented foods — including yoghurt, kefir, fermented vegetables and kombucha — significantly increased microbiome diversity and reduced markers of immune activation, even outperforming a high-fibre diet in terms of microbiome impact. Low FODMAP fermented options include lactose-free kefir, certain hard cheeses and firm tofu.
Eat enough fibre. Total fibre intake in the UK averages around 18 grams per day — significantly below the recommended 30 grams. Fibre is the primary fuel for butyrate-producing bacteria, and butyrate is one of the most important compounds for colonic health and gut lining integrity. Increasing fibre intake through oats, legumes (in Low FODMAP portions), vegetables, fruit and wholegrains is one of the most evidence-supported dietary strategies for microbiome health.
Reduce ultra-processed foods. A study published in Cell Host and Microbe in 2022 found that ultra-processed food consumption was associated with reduced microbiome diversity and lower levels of butyrate-producing bacteria. Emulsifiers — including carboxymethylcellulose and polysorbate 80, commonly found in protein powders and processed foods — have been shown to disrupt the mucus layer protecting the gut lining and alter microbiome composition in animal studies. Choosing additive-free, minimally processed foods — including certified clean protein powders — is a meaningful step for microbiome health.
Eat enough protein. Adequate protein intake supports the integrity of the gut lining, which is composed largely of protein structures including tight junction proteins and mucins. Protein malnutrition is associated with increased intestinal permeability — leaky gut — and reduced immune function. For women, meeting protein targets of 1.2 to 1.6 grams per kilogram of body weight is particularly important for gut health as well as muscle and bone health.
The IBS Complication — Feeding Your Microbiome Without Triggering Symptoms
For people with IBS, the standard microbiome-supporting advice creates a dilemma. Many of the foods best supported by the evidence for microbiome health — garlic, onion, leeks, artichoke, apples, high-fibre legumes — are also among the highest FODMAP foods and will trigger significant IBS symptoms in sensitive individuals.
The resolution is not to avoid these foods forever, but to approach them strategically. The Low FODMAP elimination and reintroduction process identifies which specific FODMAPs are your personal triggers. Many people with IBS can tolerate moderate amounts of some FODMAP-containing prebiotic foods — particularly after their gut has been given time to settle during the elimination phase.
In the meantime, there are prebiotic options that are either Low FODMAP or low enough in FODMAPs to be tolerated in normal portions. These include oats, flaxseed, firm bananas, blueberries, kiwi fruit, potato (cooked and cooled, which increases resistant starch content), and certain wholegrains.
Resistant starch — found in cooked and cooled potatoes, rice and pasta, as well as unripe bananas — deserves special mention. It bypasses digestion in the small intestine and arrives intact in the large intestine where it serves as an excellent prebiotic substrate for butyrate-producing bacteria. It is generally well tolerated by people with IBS and provides meaningful microbiome support without triggering FODMAP symptoms.
Protein Powder and the Gut Microbiome
The protein supplement you choose has direct implications for your gut microbiome. Commercial protein powders frequently contain emulsifiers, artificial sweeteners, thickeners and prebiotic fibres that can disrupt the gut microbiome or trigger IBS symptoms.
Artificial sweeteners including sucralose and saccharin have been shown in research published in Cell to directly alter gut microbiome composition in ways that impair glucose tolerance. Inulin and chicory root — added as prebiotic fibres in many protein powders — are high FODMAP and will exacerbate IBS symptoms in sensitive individuals despite their prebiotic properties.
Choosing a certified additive-free protein powder removes these variables from your daily nutrition. That Protein's certified Low FODMAP range contains no artificial sweeteners, no emulsifiers, no inulin and no chicory root — just organic plant ingredients tested and certified to be safe for sensitive guts. Used alongside a varied plant-rich diet, it supports rather than undermines the gut ecosystem you are working to build.
Lifestyle Factors That Also Matter
Diet is the most powerful lever for microbiome health but it is not the only one. Chronic stress suppresses beneficial bacteria and promotes the growth of pathogenic species — a connection mediated by the gut-brain axis and the stress hormone cortisol. Regular physical activity is consistently associated with greater microbiome diversity — even moderate exercise like walking produces measurable differences. Adequate sleep supports the circadian rhythms of gut bacteria, which — like the rest of the body — follow a roughly 24-hour cycle. Antibiotic use has significant short-term effects on microbiome composition, and where antibiotics are necessary, a course of probiotics during and after treatment is supported by reasonable evidence.
A Final Word on Probiotics
Probiotic supplements are one of the most commercially marketed products in the gut health space and among the most widely misunderstood. The evidence for specific probiotic strains in specific conditions — particularly Lactobacillus rhamnosus GG for antibiotic-associated diarrhoea and certain strains for IBS — is reasonably strong. The evidence for generic probiotic supplements improving general wellbeing in healthy people is considerably weaker.
For people with IBS, the evidence for specific multi-strain probiotics is promising but inconsistent. The most robust strategy remains dietary — building a diverse, plant-rich, additive-free diet that creates the conditions in which your own beneficial bacteria can thrive.
Explore That Protein's certified Low FODMAP range at thatprotein.com — free UK delivery on orders over 40 pounds.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. The research referenced reflects current understanding which continues to evolve. Please consult your GP or a registered healthcare professional for personalised guidance on digestive health.