Why Does Your Bloating Keep Coming Back? The Gut Story Behind SIBO

your stomach is flat when you wake up and looks six months pregnant by the evening, or because you've already worked out that garlic and onions do something unpleasant to you, or because you've done a round of FODMAP and felt a bit better but never quite right, I want to talk to you about SIBO.

Small Intestinal Bacterial Overgrowth. It sounds technical, but the idea behind it is simple, and once you understand it, a lot of confusing symptoms start making sense together instead of looking like a random list.

Your small intestine is supposed to be quiet

Most of your gut bacteria live in the large intestine, the colon. Your small intestine, especially the section right after your stomach, is meant to stay relatively low in bacteria. It's kept that way on purpose, partly by stomach acid, and partly by a constant supply of digestive secretions that keep things moving through and washing clean.

SIBO happens when bacteria build up in the small intestine anyway, usually somewhere around 100,000 organisms where there should be far fewer. And it isn't simply a case of "gut bacteria, wrong postcode." More than half of SIBO cases involve a particular family of bacteria (Klebsiella and E. coli are common culprits) that are known to trigger inflammation and are linked to a leakier gut lining. That's part of why SIBO so often comes with symptoms that seem to have nothing to do with digestion at all.

Meet your gut's gatekeeper

Here's the part that changed how I think about bloating. Between meals, your small intestine runs a housekeeping wave called the Migrating Motor Complex, or MMC. Roughly every 90 to 120 minutes when you're not eating, this wave sweeps through and clears out any leftover food and bacteria, keeping the small intestine tidy.

Think of it as the cleaner who comes through your house every couple of hours while you're out, so nothing has the chance to build up. When that cleaner stops turning up, mess accumulates. If your MMC is weak or not firing properly, bacteria that should be swept along instead settle in and start fermenting food where it shouldn't be fermented. That fermentation is where a lot of your gas, bloating and discomfort is actually coming from.

This is also why grazing all day, or sipping milky tea constantly between meals, can work against you. Your body reads that as eating. The MMC only runs during a proper fasted gap, so if there's rarely a gap, the cleaner never gets called in.

The food poisoning connection

This is the bit that surprises most people. A significant number of SIBO cases, particularly the type that shows up as urgent, loose, post-meal diarrhoea, can be traced back to a specific chain of events that starts with a bout of food poisoning, sometimes years earlier.

It goes something like this: an infection with something like campylobacter, E. coli, salmonella or shigella releases a toxin as part of the infection itself. In some people, the immune system's response to that toxin cross-reacts with a protein called vinculin, which sits in the nerve cells that act as your gut's pacemaker. If those pacemaker cells get damaged, the MMC weakens. And a weaker MMC means bacteria are more likely to build up. It's a genuinely traceable mechanism, not a vague "gut got upset once" story, and it's one of the reasons a single bad stomach bug can leave someone with digestive symptoms for years afterwards. Each further episode of food poisoning makes the next overgrowth easier to develop too, because the gatekeeper is already a little weaker.

What it can look like

SIBO shows up differently depending on the type (more on that in the next post), but common threads include bloating that's worse after meals or builds through the day, altered bowel habits, food that seems to sit heavily, fatigue and brain fog, reflux, joint pain or skin flares, and low iron, ferritin or B12 that never quite budges no matter how much you supplement. If you've been told your fibre intake or your probiotic should be helping and it just isn't, or if things flared right after a stomach bug, that's exactly the pattern worth paying attention to.

Why "just kill the bacteria" isn't the whole answer

The instinct with SIBO is often to go straight for an antimicrobial and clear the overgrowth. That can work in the short term, but if nothing else changes, the same conditions that allowed the overgrowth in the first place are still there waiting. The more useful question isn't just "how do I get rid of this," it's "what allowed this to happen." Motility, digestive secretions, stress, and diet pattern all deserve a look alongside reducing the bacterial load itself, otherwise relapse is common.

Where to go from here

If any of this sounds familiar, the next step is understanding which type of SIBO you might be dealing with, because hydrogen, methane and hydrogen sulphide overgrowth are genuinely different conditions with different treatment approaches. I'll walk through that next.

In the meantime, if you recognise yourself in this and want to get to the bottom of it properly rather than guessing, that's exactly the kind of thing we work through together at Vale of Health. Book a consultation and let's find out what's actually going on.