Why "Eat More Fibre" Is Dangerously Incomplete Advice

If one piece of health advice has universal agreement, it’s "eat more fibre." Doctors say it. Nutritionists say it. Your grandmother says it, though she’d put it as "eat your sabzi and roti properly." It sounds simple, universal, harmless.

It isn’t that simple. For some people, blindly piling on fibre makes gut problems worse, sometimes a lot worse. The advice isn’t wrong, exactly. It’s just so incomplete that following it without the details can backfire.

Not all fibre is the same

"Fibre" lumps together several very different compounds that behave in completely different ways inside you.

Soluble fibre dissolves in water and forms a gel: oats, barley, the inside of an apple, dal. It slows digestion, steadies blood sugar, and can lower cholesterol. Some soluble fibres also get fermented by gut bacteria into short-chain fatty acids, especially butyrate, premium fuel for the cells lining your colon.

Insoluble fibre doesn’t dissolve. It adds bulk and keeps things moving: wheat bran, vegetable skins, cauliflower stalks. Gut bacteria don’t ferment it much, so it makes few SCFAs, but it prevents constipation.

Resistant starch resists digestion in the small intestine and reaches the colon intact, where bacteria ferment it. Cold rice (next-day pulao), cooked-and-cooled potatoes, raw bananas. It’s one of the most potent prebiotics known, strongly feeding beneficial bacteria like Bifidobacterium and Ruminococcus bromii.

Prebiotic fibres are fermentable fibres that selectively feed good bacteria. Inulin (garlic, onions, chicory root), fructooligosaccharides (FOS, from bananas and asparagus), and galactooligosaccharides (GOS, from legumes).

Each type feeds different bacteria and does different things. "Eat more fibre," with no type attached, leaves out the part that decides whether it helps.

When more fibre makes things worse

Here’s where the standard advice turns risky. For some gut conditions, more fibre, especially the wrong kind, makes symptoms much worse.

If you have Irritable Bowel Syndrome (IBS), which studies in the Indian Journal of Gastroenterology estimate affects 10-15% of Indians, the type matters enormously. Insoluble fibre, the wheat bran and raw vegetables doctors usually push, can actually increase bloating, gas, and pain in IBS. A study in the British Medical Journal found bran supplementation worsened symptoms in a sizeable share of IBS patients who tried it.

Soluble fibre is the opposite. Psyllium husk (isabgol, already in most Indian homes) has been shown to ease IBS symptoms. NICE guidelines specifically recommend soluble fibre over insoluble for IBS.

Same word, opposite effects.

For Small Intestinal Bacterial Overgrowth (SIBO), it gets trickier. In SIBO, colon bacteria have crept into the small intestine. Eat highly fermentable fibres (inulin, FOS, GOS) and those misplaced bacteria ferment them right there, making hydrogen and methane in a stretch of gut that isn’t built for fermentation. The result is severe bloating, distension, pain, sometimes diarrhoea.

Many SIBO patients say standard "eat more fibre and take prebiotics" advice made them far worse. Not because fibre is bad. Because their gut geography is different, and fibre that helps a healthy gut wreaks havoc when bacteria are in the wrong place.

Here’s where the standard advice turns risky.

Your bacteria decide what happens to the fibre you eat

Even without IBS or SIBO, fibre responses vary hugely based on your existing bacteria.

If your microbiome is rich in primary fibre degraders like Ruminococcus bromii, Bacteroides thetaiotaomicron, and Prevotella copri, you break down complex plant fibres efficiently and make beneficial SCFAs. More fibre then means a healthier gut, more regular bowels, lower inflammation.

But if you’re short on those primary degraders (after antibiotics, chronic stress, or a long low-fibre stretch), loading up on fibre creates a traffic jam. It reaches your colon, but there aren’t enough bacteria to process it. It sits there, half-fermented by whatever’s around, making excess gas and discomfort.

A Stanford study found that when low-fibre eaters suddenly went high-fibre, those with low microbial diversity had more gas and bloating during the switch. Their microbiomes needed weeks to months to recruit and grow the bacteria for the new load.

That’s why "just eat more fibre" so often fails the people who need it most. The very people with poor gut health and low diversity are the least equipped for a sudden fibre jump.

Want to know what your own gut actually needs? Take the BioMeBar gut assessment →

A smarter approach to fibre

None of this means fibre is bad. The evidence for its benefits is overwhelming. Higher-fibre populations have lower rates of colorectal cancer, heart disease, type 2 diabetes, and death from all causes. Fibre genuinely matters.

But the approach matters too. For most people, especially with existing gut issues, go low and slow. Start with small amounts of soluble, well-tolerated fibres (cooked dal, oats, isabgol) and build up while watching how you respond. Add one fibre type at a time. Give your microbiome time to grow the bacteria for each.

The smarter move is to know what’s in your gut before you start. If you’re already rich in Prevotella and Ruminococcus (common on traditional Indian diets full of dal and whole grains), you can handle a broad range of fibres. If you’re depleted there, start gentle and build gradually.

That’s the personalised thinking BioMeBar brings. Instead of generic fibre advice, it reads your individual profile and helps work out not just whether you need more fibre, but which types your specific community can use, and which might do more harm than good. With fibre, the details matter far more than the headlines suggest.

Stop guessing. See what is actually in your gut.

BioMeBar profiles your unique microbiome and personalises recommendations to what is genuinely there, because with trillions of organisms running your biology, one-size-fits-all does not make sense.