Experiencing a few days of gut trouble, therefore, is an expected though unfortunate side effect of many antibiotics. This alone does not indicate that the antibiotic has permanently disrupted your microbiome – the trillions of bacteria and their genetic material living in our guts – although that’s a common fear.
And to make matters more confusing, anywhere from one in 10 to one in four people who experience an acute infection such as from a bacterial stomach infection will go on to develop long-term GI symptoms like irritable bowel syndrome that have nothing to do with antibiotics.
Parsing out what symptoms, if any, were ever because of the antibiotic, changes to the microbiome – or some combination thereof – can be genuinely difficult.
How antibiotics can affect the microbiome
But here’s what we have known for nearly a decade: exposure to antibiotics does cause short-term changes to the microbiome. Our microbiomes are resilient enough to bounce back close to our baselines within a few weeks, even after extremely powerful antibiotics. (During early childhood, it can be a different story – our microbiomes are more malleable then and more vulnerable to lasting disruption.)
We also know that everyone may react differently to antibiotics because we all have different microbiomes to begin with – people who are immunocompromised, for example, or taking certain medications such as proton pump inhibitors may have more fluctuations in their microbiome as a result of antibiotics – which could put them at higher risk of an infection by a type of bacteria called C. difficile.
What we hadn’t known – until recently – is how long those changes could persist. A recent Swedish study published in Nature Medicine has given us some of those answers.
Looking at prescription records and analyses of the microbiomes of nearly 15,000 people, researchers found that for some, even a single course of antibiotics led to persistent changes years later. Three broad-spectrum antibiotics studied were mainly responsible: clindamycin, flucloxacillin and fluoroquinolones. At the same time, some of the most common antibiotics prescribed in the United States – amoxicillin, macrolides such as azithromycin and cephalosporins such as cephalexin – were associated with far more modest effects.
So what does this tell us? Different antibiotics affect the gut differently – some with long-term impact – and this can depend on both the antibiotic and the person. What we don’t yet know is what this does or doesn’t mean for our health.
Do probiotics help?
I get the instinct to take a probiotic supplement while taking antibiotics. The problem is: it’s been studied, and the evidence isn’t there. A 2023 meta-analysis of several trials found that supplementing with probiotics while on antibiotics does very little.
You might think, well, what’s the harm? Consider this: one small study published in 2018 in Cell found that people who took probiotics after antibiotics took far longer to recover their baseline microbiome compared with those who didn’t take probiotics.
There’s slightly better evidence that probiotics may help prevent C. difficile infection among people at higher risk (such as if you’re hospitalised or immunocompromised) – so if that’s you, it’s worth talking to your doctor. For most people, though, it’s probably better to save your money.
Three ways to bolster your microbiome
We certainly need more research in this area, but there are ways to support your microbiome that are backed by stronger science. They’re actually the principles that I organise my own meals around. So this is a great time to make some changes that, I hope, would form a lifelong habit:
Eat a high-fibre diet
Your microbes ferment fibre and in turn produce beneficial short-chain fatty acids. A psyllium fibre supplement is an easy way to meet your fibre goals, which for women under 50 is 25g of fibre per day and for men under 50 is 38g. For women over 50, it’s 21g and for men over 50; shoot for 30g.
Include a variety of plant-based fibre sources in your diet
Hitting those fibre goals is just the backbone, in my opinion – variety is the part that really matters. A major study from 2018 found that it was the variety of plants in your diet that best predicted microbial diversity, one of the hallmarks of a healthy microbiome. People think all fibre is the same – it’s not. Different types of fibres feed different bacteria. So eating just one type of fibre – even a lot of it – preferentially feeds just a small slice of your microbial community, while the rest may go hungry.
Eat probiotics food every day such as Greek yoghurt or kimchi
Anyone who knows me has heard me cite this study at dinner parties (I’m a treat, I know): In a seminal Stanford randomised controlled trial, researchers assigned healthy adults to either a high-fibre diet or to changing nothing else in their diet except to eat as many fermented foods as possible. Then they tracked participants over 10 weeks. Remarkably, the fermented-food group showed greater increases in microbial diversity and – here’s the kicker – had a decrease in the level of 19 different inflammatory proteins in their blood. The more servings of fermented foods they ate, the stronger the effects.
What I want my patients to know
Antibiotics are very important to fight infections. If you need them, take them. It would be extremely rare for any doctor to advise you to skip an appropriate course of antibiotics because of the hypothetical effects on the gut.
Still, it’s important that we use antibiotics only when appropriate and choose the narrowest effective option when possible. One scenario to avoid is requesting antibiotics for a viral infection, such as the common cold. Antibiotics don’t inhibit viruses, only bacteria, so they won’t touch your cold – but will just expose you to potential side effects.
And there are also situations where the medical guidelines have evolved because of new data. One that often surprises my patients is that for otherwise healthy people who get diverticulitis, a condition where a small section of their colons become inflamed, we actually don’t routinely prescribe antibiotics any more. The data now shows that most people recover just fine without them, sparing them any side effects in the process.
And remember, once you start a course of antibiotics for an infection, it’s just as important that you finish that full course to ensure the infection is fully eliminated and to stop the development of antibiotic-resistant bacteria.