Antibiotics can have troublesome consequences on our guts, linked with a whole host of disorders and diseases down the line – but how worried should we be? By Hatty Willmoth.

Antibiotic medicine is powerful stuff. Those who have taken it to combat a stubborn infection know how much relief it can bring.

But, in fixing the problem at hand, antibiotics can have adverse effects on microorganisms that we want in our bodies.

That’s according to multiple reviews of hundreds of scientific studies investigating the consequences of antibiotics on gut health (for example from 2015, 2016, September 2020 and November 2020).

The research is clear: when it comes to the gut, antibiotics can be seriously disruptive.

What is the gut microbiome?

There are trillions of bacteria, yeasts and other microbes living in our digestive systems, mostly in the small and large intestine.

A group of microbes in a single environment are collectively called a ‘microbiota’, and together with their habitat can be referred to as a ‘microbiome’.

Our gut microbes break down food and absorb nutrients, and are also central in a variety of non-digestive systems such as immunity, the production of serotonin (our ‘happy’ chemical), and the regulation of metabolism.

The gut is also closely connected to the brain – a relationship known as ‘the gut-brain axis’ – so a healthy gut supports mental wellbeing.

A gut microbiome is a bit like a fingerprint – because each person has different amounts of different types of microorganisms in their guts – except the microbiome changes over time based on diet, environment and life stage.

Microbiota differ geographically and are shaped by the exchange of germs with people in our households, neighbourhoods, and friendship groups.

The ‘healthiness’ of a gut is generally measured by the quantity and variety of so-called ‘good’ bacteria: the more, the better.

What are antibiotics?

Antibiotics are substances used to kill bacteria and to treat bacterial infections, most commonly of the respiratory and urinary systems, i.e. for chest infections and UTIs.

The discovery of the antibiotic properties of penicillin is often considered a seminal moment of the 20th century, because antibiotics are so effective against malignant bacteria.

Since then, their use has become increasingly commonplace; between 2000 and 2015 worldwide antibiotic use rose by 65%.

However, the use of antibiotics encourages the proliferation of antibiotic-resistant bacteria, so in recent years antibiotics have been used more sparingly in the UK.

What do antibiotics do to the gut?

Antibiotics address infection by killing unwanted bacteria. However, they also kill other unrelated bacteria in our system – including the ‘good’ ones in our gut – reducing the diversity and quantity of our gut bacteria, so it becomes less healthy overall.

And, as antibiotics kill off some microbes, other strains can proliferate, notably antibiotic-resistant bacteria.

This can result in ‘dysbiosis’: an imbalanced microbiome, with an overgrowth of certain strains of bacteria and yeasts.

Gut dysbiosis can lead to gut disorders such as irritable bowel syndrome (IBS), Crohn’s disease, colitis and infections; for example Clostridium difficile, which can be particularly harmful.

It has also been linked to the development of conditions such as asthma and food allergies, and can affect other processes impacted by the gut microbiome, such as the immune system.

There is growing evidence too that an imbalanced gut can increase the risk of diseases such as Parkinson’s, multiple sclerosis and Alzheimer’s.

And gut dysbiosis might increase the likelihood of mental health disorders such as depression, anxiety and psychosis.

It can even affect the long-term risk of metabolic disorders such as obesity and diabetes. In fact, a 2020 review in Frontiers reported: “It is now widely accepted that the increased prevalence of obesity over the past 30 years may also be attributable to alterations in gut microbiota composition.”

A healthy gut is implicated in so many bodily processes, so it follows that gut damage can have wide-reaching effects.

How worried should I be?

This all sounds rather damning for antibiotics, but they do “have a place”, says Dr Kirstie Lawton, an AfN-registered nutritionist, BANT-registered nutritional therapy practitioner and module coordinator at the Institute for Optimum Nutrition.

“[Nutritional therapists] really don’t want people to get so scared that they don’t take [antibiotics] when they really need them,” she says.

“If somebody has something quite dangerous, then it’s really not for nutritional therapists to tell somebody not to take medication, because that’s between the doctor and the patient.”

Also, when antibiotics are taken by adults, the gut will likely bounce back. Multiple studies have observed that the guts of most individuals recover within a few weeks, although for some people it may take months or years.

Serious long-term damage is more likely when antibiotics are taken during infancy or early childhood, when the microbiome is still developing.

In that case, there is a stronger association between antibiotic exposure and asthma, allergies and airway illnesses, as well as metabolic issues such as obesity in later life.

Even then, steps can be taken to support the gut.

What can I do?

Lawton recommends “only taking [antibiotics] if it’s really necessary” and taking steps to “support your gut throughout”.

“Usually, if someone is taking antibiotics, we recommend that they take probiotics at alternate ends of the day,” she says. “That’s the general guidance.”

Probiotics are foods that contain live microbes, which can replace and bolster lost microbial communities in the gut. Probiotic foods include yoghurt, kefir, sauerkraut, miso, kombucha, and kimchi.

In clinic, Lawton says nutritional therapy practitioners may recommend a yeast-based probiotic such as Saccharomyces boulardii to restore balance.

Saccharomyces is used a lot,” she says. “There’s a lot of research supporting its use for antibiotic driven diarrhoea, so that’s something we use quite frequently.”

In a nutritional therapy clinic, Lawton says: “If someone comes to us and they’ve taken antibiotics, [our recommendations] can really depend on what the aftermath of that looks like … [and] the symptoms of the client.

“It might include antimicrobials to kill off anything that’s overgrown that we wouldn’t want there. It might include prebiotics to help regrow things like bifida bacteria that may have been killed off.

Prebiotics encourage the growth of certain microorganisms, and include Jerusalem artichoke, asparagus, leeks, onions, garlic, oats, chicory and beans.

And to support gut health in the longer term, experts suggest aiming to eat 30 plants per week, because consuming different plant fibres and compounds helps develop microbial diversity in the gut.

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