Professor Paul Clayton on the single most powerful lever for gut health, and it's not probiotics.
There is a reason the gut is sometimes called the body's second brain. It processes nutrients, trains the immune system, influences mood, regulates inflammation, and, perhaps most critically, determines whether the rest of your biology operates the way it should. When gut health is good, you may not notice it at all. When it is not, everything else tends to shift.
The good news is that the gut is responsive. Unlike genetics or ageing, it is a system that can be meaningfully improved through the right daily inputs. And the starting point, the single most powerful lever you have, is one that most people underestimate entirely: fibre.
1. Start With Fibre: The Foundation of Everything
If there is one thing that almost universally distinguishes the gut microbiome of healthy, long-lived populations from those in the modern industrialised world, it is fibre intake. Blue Zone communities (in Sardinia, Okinawa, Ikaria, and elsewhere) consume between 40 and 60 grams of dietary fibre per day through traditional diets rich in legumes, root vegetables, whole grains, and seasonal produce. The average adult in the UK or US gets closer to 15 to 18 grams. And even that figure masks significant variation in fibre quality. Fibre is the primary food source for the trillions of bacteria that live in your gut. Without it, these bacteria have nothing to ferment. Without fermentation, the short-chain fatty acids (SCFAs) that fuel your gut lining, regulate immune responses, and reduce systemic inflammation cannot be produced.
The downstream consequences of insufficient fibre intake such as gut imbalance, poor digestion, inflammation and sluggish motility, are not coincidental. They are predictable. The dietary target that research increasingly supports, and that Professor Paul Clayton has long argued for, is 15 grams of diverse prebiotic fibre daily. Not total fibre; prebiotic fibre specifically. The kind that feeds beneficial bacteria rather than passing through inert.
"The modern gut crisis is fundamentally a fibre crisis. We have stripped from our diets the very substrate that gut bacteria evolved to eat over hundreds of thousands of years." - Prof. Paul Clayton PhD
Why fibre length matters
Not all fibre behaves the same way in your gut and length is the reason why. This is a distinction that supplement formulations rarely account for, but that makes a profound difference to what actually gets fermented, and where.
Short-chain fibres, such as inulin and FOS (fructooligosaccharides), are rapidly fermented in the upper sections of the colon. They provide a quick burst of bacterial activity but are exhausted before reaching the distal colon, the section of the bowel that, according to emerging research, may be most critical for long-term disease prevention. Short fibres leave the lower gut essentially unfed.
Long-chain fibres, by contrast, are more structurally resistant. They travel further through the colon before fermenting, reaching the descending and sigmoid sections where bacterial populations are dense and fermentation products have the greatest systemic reach. The result is a more complete, whole-colon effect; closer to the profile seen in traditional diets where fibre diversity was naturally high.
A gut health strategy that accounts for fibre length, using a combination of short, medium, and long-chain prebiotic fibres, is materially different from one that simply counts grams. This is the principle behind fibermaxxing done properly: not just more fibre, but smarter fibre, matched to the full length of the gut.
How to hit 15g of prebiotic fibre daily
Through food alone, this requires deliberate effort. The richest dietary sources of prebiotic fibre include: chicory root, Jerusalem artichokes, garlic, leeks, onions, asparagus, green bananas, oats, flaxseed, and legumes. Variety matters as much as quantity; different fibre types feed different bacterial strains.
For most people, combining high-fibre whole foods with a targeted fibre supplement is the most practical way to consistently reach the 15g threshold. The key is choosing a supplement that delivers genuine fibre diversity and length complexity, not just a single isolated fibre source marketed as a complete gut solution.
2. How to Naturally Cleanse Your Stomach and Intestines
Searching for a gut cleanse often leads to products promising dramatic, rapid results - activated charcoal shots, three-day liquid diets, herbal laxative blends. The evidence behind these is largely absent. The gut does not need a purge. What it needs is an environment in which its own natural cleansing mechanisms can function correctly.
The gut has an elegant self-cleaning system called the migrating motor complex (MMC), a wave of muscular contractions that sweeps the intestines between meals, clearing residue and bacteria from the small intestine into the large bowel. This system activates during fasting periods, which is one reason eating within a structured window, rather than grazing continuously, supports better digestive function.
Supporting your body's natural gut reset comes down to a few consistent habits:
- Adequate hydration. Water is essential for mucosal lining integrity and stool transit. Aim for 1.5 to 2 litres daily. Herbal teas, particularly ginger and peppermint, may also support digestion and gut motility.
- Movement. Exercise for gut motility is well-documented. Even brisk walking for 30 minutes increases intestinal transit time and reduces the risk of sluggish digestion. Yoga and diaphragmatic breathing can also help to relax gut muscles and ease discomfort.
- Fasting windows. Eating within an 8 to 10 hour window gives the MMC time to activate. This is not about restriction, it is about giving the gut the quiet time it needs to clean house.
Reducing ultra-processed foods (UPFs). These actively disrupt the gut lining and crowd out beneficial bacteria. A gut cleanse at home does not need a detox kit. Removing refined carbohydrates, artificial emulsifiers, and excess sugar for even two weeks produces measurable improvements in gut bacterial diversity.
3. What Causes Gut Imbalance?
Gut imbalance, sometimes called dysbiosis, occurs when the bacterial community in the gut shifts away from a healthy, diverse state toward one dominated by fewer, potentially harmful species. The causes are multiple and often cumulative. Chronic low fibre intake is arguably the most significant driver. Without sufficient prebiotic fuel, the bacteria that produce anti-inflammatory SCFAs such as Bifidobacterium, Lactobacillus, Faecalibacterium prausnitzii, gradually decline, leaving space for opportunistic bacteria to proliferate.
Antibiotic courses, even short ones, can deplete bacterial populations significantly. Research suggests full recovery can take months or longer without targeted intervention. Chronic stress, poor sleep, a sedentary lifestyle, alcohol, and the widespread use of proton pump inhibitors (such as omeprazole) are all associated with changes in gut bacterial composition. So is frequent consumption of ultra-processed foods, which contain ingredients that disrupt the mucous barrier lining the gut wall.
Understanding what causes gut imbalance matters because it reframes the solution: rather than a one-time cleanse, what the gut requires is consistent, sustained nutritional support that rebuilds and maintains the bacterial community over time.
4. Fermented Foods and the Gut: What the Evidence Actually Says
Fermented foods have had a considerable moment in popular wellness culture, and there is good science behind the enthusiasm, up to a point. Yoghurt, kefir, kimchi, sauerkraut, miso, and kombucha all contain live bacteria that can temporarily increase microbial diversity in the gut and may support immune function.
A 2021 Stanford study published in Cell found that a high-fermented-food diet significantly increased microbiome diversity and reduced inflammatory markers; more so than a high-fibre diet alone over the same period. But the researchers were careful to note that the two approaches are not competing: fermented foods introduce new microbial populations, while prebiotic fibre sustains them.
The most effective approach combines both. Think of fermented foods as planting seeds; prebiotic fibre as watering them. Without the fibre, the newly introduced bacteria have nothing to eat, and their colonisation is transient.
For the best dietary sources of fermented foods for gut health, focus on naturally fermented options (live cultures listed on the label, unpasteurised where possible) rather than heat-treated versions which have lost their bacterial content.
5. Natural Remedies for Gut Health: What Is Worth Your Attention
The market for natural gut remedies is crowded and often contradictory. Here is a clear-eyed look at what the evidence actually supports:
- Ginger: Well-studied for its effect on gut motility and nausea. Ginger accelerates gastric emptying and may reduce bloating. Use fresh ginger in food or tea, or as a standardised supplement.
- Unmodified potato starch: A resistant starch that acts as a potent prebiotic, fermenting slowly in the colon to produce butyrate, one of the most important SCFAs for gut lining integrity.
- Peppermint oil: Evidence supports its use for IBS symptoms, particularly gut cramping, through a relaxation effect on smooth muscle.
- Slippery elm and marshmallow root: Both are mucilaginous fibres that soothe the gut lining and may support barrier function, though clinical evidence is less robust than for the above.
- Digestive enzymes: For those with specific enzyme insufficiencies, supplemental enzymes can support digestion. For the general population, the more impactful intervention is addressing the upstream cause (gut bacterial imbalance) rather than managing downstream digestive symptoms.
6. What to Take for Gut Health: A Guide to Supplements
The gut health supplement market is one of the most rapidly growing, and most confusing, areas of the wellness industry. Probiotic supplements dominate shelf space and marketing spend, but the evidence for standard probiotic capsules in otherwise healthy adults is more nuanced than most brands acknowledge. Probiotics introduce live bacteria into the gut. The challenge is that most probiotic bacteria do not colonise the gut long-term, they pass through. Their benefit is often temporary and contingent on what they encounter in the existing gut environment. If the gut bacterial community is depleted, poorly diverse, or inadequately fed, probiotic bacteria have limited capacity to thrive and multiply. Prebiotics work differently. Rather than introducing bacteria from outside, they nourish and selectively feed the beneficial bacteria already present.
This is why prebiotic fibre supplementation is increasingly viewed as the more durable intervention; it improves the gut environment itself, not just its temporary inhabitants. The most evidence-supported approach for gut health is to prioritise prebiotic fibre supplementation, ideally from multiple fibre types covering a range of chain lengths, alongside a diet rich in naturally fermented foods and diverse plant matter.
For those looking at complete gut repair rather than isolated supplementation, the emerging category of whole-gut prebiotic fibre complexes, designed to target all sections of the colon from start to finish, represents the most sophisticated iteration of this thinking.
The Bottom Line
The path to better gut health is not dramatic. It does not require a three-day cleanse, a liquid diet, or a cabinet full of probiotic capsules. What the gut responds to is sustained, intelligent nutritional support, starting with the single input it has always needed most. Fibre first.
Fifteen grams of diverse prebiotic fibre daily, drawn from multiple sources and covering the full range of fibre lengths. Pair that with naturally fermented foods, adequate hydration, regular movement, and a consistent eating window. Reduce the ultra-processed inputs that disrupt bacterial communities and damage the gut lining. And choose supplements that work with the gut's own biology rather than around it.
The populations who age well, who maintain gut health, metabolic resilience, and cognitive function well into their eighties and nineties, are not doing anything exotic. They are eating, moving, and living in ways that keep the gut fed. That is the standard worth aiming for.
