Bloated After Fibre? Gas Might Not Be The Problem
You had porridge for breakfast. At lunch you had the lentil soup, because it's full of fibre and fibre's meant to be good for your gut. By three o'clock your waistband's digging in, and you've undone the top button under the desk where nobody can see. You look six months pregnant and you feel worse than you look.
And you did the right thing. That's the bit that stings. You've read the leaflet, you've eaten the vegetables, and you've ended up swollen and sore and wondering what on earth you're doing wrong.
You might not be doing anything wrong. A team in Nottingham put people with IBS inside an MRI scanner to find out where the bloating comes from, and what they found wasn't what most of us would guess.
This week's research: same gas, very different feeling
In 2017 a team from the University of Nottingham, led by Giles Major and Robin Spiller, published a study in the journal Gastroenterology. They took 29 adults with Irritable Bowel Syndrome (IBS) who had bloating, and 29 adults without IBS.
Everyone came in on three separate days, at least a week apart. Each time they drank a 500ml drink with 40g of carbohydrate in it. One day it was glucose, which your body absorbs easily, so it acts as the comparison. One day it was fructose, a fruit sugar. And one day it was inulin.
Inulin's a type of fibre. You'll find it in onions, garlic, leeks and chicory, and it gets added to a lot of high-fibre and "gut health" products. Your small bowel can't digest it, so it travels on to your large bowel, where your gut bacteria ferment it. Fermenting makes gas.
Then the researchers watched. For five hours they scanned everyone's bowels with MRI to see how much water and gas was inside. They also measured hydrogen on people's breath, which goes up when bacteria are fermenting.
Here's what they found.
Inulin made more gas in the large bowel. It did that in the IBS group, and it did it in the group without IBS. The scans and the breath tests looked much the same in both.
The difference was in how people felt. After inulin, 13 of the 29 people with IBS had a clear rise in symptoms, compared with 6 of 29 after the glucose drink. The people without IBS had the same gas and felt far less.
And among the people with IBS who reacted to inulin, the ones who had the most gas felt the worst. But their gas levels weren't higher than those of the people with IBS who didn't react, or the people without IBS. The authors' conclusion is right there in the title of their paper: symptoms came from the bowel being sensitive to stretching, rather than from making too much gas.
Now the limits, because there are some. It's a small study, in one hospital. A 40g drink of inulin in one go is a lot more than you'd get from a bowl of soup, so it's a test in a lab rather than a normal day's eating. And it's nearly ten years old. It's still one of the clearest pictures anyone's taken of what bloating looks like from the inside, which is why it's still quoted.
Why this matters for you. If you've spent years thinking your gut must be making loads of extra gas, this study says that might not be what's going on. Your gut may be making ordinary amounts. It's how strongly that ordinary amount gets felt that's different. That's a real, physical thing, and it's got a name.
Why your gut feels what other guts don't
The name is visceral hypersensitivity. Visceral means your insides. Hypersensitivity means extra sensitive. Put together, it means your gut sends up a louder signal than someone else's would for the same amount of stretch.
IBS is described as a disorder of gut-brain interaction. Your gut and your brain talk to each other all day long, through nerves, hormones, the immune system and even your gut bacteria. In IBS that conversation's become oversensitive. The gut sends a message about some gas, and by the time your brain's read it, it says "pain" or "something's wrong".
We looked at the brain's side of this last week in Why You Feel Almost Every Emotion In Your Stomach. This week's the same story told through a bowl of lentil soup.
So what about fibre itself? You don't need to give it up. The British Society of Gastroenterology's 2021 guideline for IBS says soluble fibre, such as ispaghula (you'll know it as psyllium), helps overall IBS symptoms and tummy pain. It says to start low, around 3 to 4g a day, and build up slowly so you don't get bloated. It also says insoluble fibre, like wheat bran, is best avoided because it can make symptoms worse. If you want to change what you're eating, talk it through with your GP or a registered dietitian, who can look at your whole diet.
The food is one half of this. The other half is how loudly your gut reads what the food does. That second half is where my work sits.
I'm a cognitive behavioural hypnotherapist, which means I use three approaches together. Cognitive behavioural therapy works on what you expect a feeling in your gut to mean, and what you do next because of it. Mindfulness trains your attention to notice a feeling for what it is. Gut-directed hypnotherapy uses focused attention and imagery aimed at the gut. The British Society of Gastroenterology gives gut-directed hypnotherapy a strong recommendation for IBS, and NICE lists psychological approaches including hypnotherapy for IBS that hasn't improved with medication after twelve months. I can't tell you what it would do for you, and this week's study didn't test it. What the study does is show why working on the reading of the signal makes sense at all.
Your top tip this week
Describe the bloat before you blame the lunch. Next time the bloating starts, put one hand flat on your stomach and breathe out a little longer than you breathe in, four or five times. Then find a plain word for what you feel right now: tight, full, pressing, warm, stretched. Stay with that word instead of the story that comes after it, the one about what you ate and how bad the evening's going to be. On this week's evidence your gut may be reading an ordinary amount of gas at full volume, and naming what's there is a way of listening to it without turning it up further.
The takeaway
When fibre leaves you bloated, it's easy to decide your gut's broken or you're eating the wrong things. This study points somewhere kinder. Your gut may be making the same gas as anyone else and feeling it much more strongly, and that sensitivity is something you can work with.
Wherever you are right now
If you haven't had a firm diagnosis yet, start there. A diagnosis from your GP rules out what needs ruling out, and it's the first step to the support the guidelines recommend.
If you were diagnosed a while ago and you're still struggling, you're who the guidelines had in mind. And if you've cut food after food trying to stop the bloating, this week's study is worth holding on to: the problem may never have been the food.
If you're a GP or a gastroenterologist reading this, the referrer brief for gut-directed hypnotherapy, with the guideline positions set out honestly and their limits stated, is available on request.
If you'd like the science in plain English once a week, plus one thing to try, join Gut Feelings at mindyourguts.co.uk/free-relaxation-page. The free relaxation recording comes with it.
About Mind Your Guts
Mind Your Guts is the Irritable Bowel Syndrome (IBS) blog written by Kathryn Dunn, a cognitive behavioural hypnotherapist based in York and working online. One piece of gut-brain research each week, in plain language, and one thing worth trying. More at mindyourguts.co.uk/gut-feelings.
Twelve Minutes of Calm. A free relaxation recording, about twelve minutes, for the times you want to feel calmer. It's a general relaxation recording rather than a treatment for anything. Download it at mindyourguts.co.uk/free-relaxation-page and you'll also join Gut Feelings, my weekly email, which carries each new post to your inbox along with a bit extra.
Hypnotherapy works alongside conventional medical care, never in place of it. This blog shares research for general information and is not a substitute for medical advice. Always consult your GP or another relevant health professional before changing your diet. If your symptoms are new, changing, or accompanied by warning signs such as bleeding, unexplained weight loss, or persistent pain, please see your GP.
