Antibiotics are commonly prescribed to treat bacterial infections, and in some situations, they may even be used as a precaution. During a recent meningitis B outbreak in Kent, for example, more than 6,500 students were given antibiotics to reduce the risk of infection.¹
However, many people notice a familiar problem when taking antibiotics: digestive discomfort, bloating, or even diarrhoea.
If you have ever experienced this, you might have wondered why this happens. After all, antibiotics are meant to treat infections, so why do they seem to upset the gut at the same time?
How Antibiotics Affect the Gut
Antibiotics are designed to eliminate harmful bacteria causing infection. However, they do not act selectively on harmful species alone.
Research has shown that antibiotics can significantly reduce microbial diversity and alter the composition of the gut microbiome.²,³ Beneficial bacteria such as Bifidobacterium and Lactobacillus may decrease, while other bacteria may persist or even expand.
This disruption is often referred to as gut dysbiosis, a state where the balance of the gut microbiome is disturbed.
Why Digestive Symptoms Occur
The gut microbiome plays a key role in maintaining normal digestive function. When this balance is disrupted, several changes may occur:
- Altered gut motility
- Reduced production of beneficial metabolites
- Changes in water absorption
- Low-grade inflammation
These changes are thought to contribute to symptoms such as diarrhoea, bloating, and abdominal discomfort.⁴
For example, when beneficial bacteria are reduced, their ability to regulate water balance in the gut may be affected, potentially leading to looser stools.
Side Effects Vary, But The Gut Microbiome Is Just As Enormous.
Not everyone experiences noticeable symptoms after taking antibiotics. However, even in the absence of symptoms, changes in the gut microbiome may still occur.³
Recovery of the microbiome is also highly individual. Some bacterial populations may return relatively quickly, while others may take weeks or even months to recover. In some cases, certain species may not fully return to their original levels.⁵
Factors such as baseline microbiome composition, diet, and environment all influence this recovery process.
Supporting Gut Recovery
While some bacteria bounce back quickly after you finish your course of antibiotics, research shows that the gut microbiome does not always recover immediately. In some cases, certain bacterial populations may take months to fully return to their original balance.⁵
During this time, there is a risk that harmful bacteria may temporarily gain the upper hand, while the gut lining may remain sensitive or inflamed. This imbalance can contribute to symptoms such as diarrhoea, abdominal discomfort, and other digestive issues.
For this reason, supporting the gut microbiome early on may help reduce discomfort and promote a more stable recovery.
Many healthcare professionals recommend consuming probiotic-rich foods a few hours after taking antibiotics. The aim is to help replenish beneficial bacteria that may have been reduced, while limiting the opportunity for less favourable microbes to grow.
Foods naturally rich in probiotics include yoghurt, kefir, pickles, kimchi, miso, and tempeh. However, the digestive environment can be harsh, and a significant proportion of these live microorganisms may not survive long enough to reach the gut. To maximise potential benefits, these foods are best consumed regularly, in sufficient amounts, and without high-temperature cooking, as heat can reduce the viability of live bacteria.
In addition to probiotics, prebiotic dietary fibres also play an important role. Beneficial bacteria rely on these fibres, commonly found in vegetables, fruits, and other plant-based foods, as a source of nourishment. By supporting their growth and activity, prebiotics may help restore balance more effectively.
For those seeking a more consistent and targeted approach, probiotic supplements combined with prebiotic fibres may offer a practical option. Unlike natural foods, certain supplement formulations are specifically designed to protect probiotics as they pass through the harsh digestive tract, ensuring more live bacteria successfully reach the gut.
Some studies have explored the potential role of probiotics in reducing the risk of antibiotic-associated diarrhoea.⁷ For example, a large 2021 systematic review involving over 11,000 participants reported a reduction in risk in certain populations, particularly with commonly studied strains such as Bifidobacterium.⁷
Alongside these strategies, maintaining an overall balanced diet remains important. Certain dietary factors, such as excessive alcohol, artificial sweeteners, emulsifiers, and some preservatives found in processed foods, may negatively affect beneficial bacteria and potentially slow down recovery of the gut microbiome.
Conclusion: Supporting Your Gut During and After Antibiotics
Antibiotics remain an essential and effective tool in modern medicine. However, their impact on the gut microbiome helps explain why digestive symptoms such as diarrhoea and bloating are so commonly experienced. Understanding this process allows us to take practical steps to support recovery.
Fortunately, there are actionable ways to restore this microbial balance. Diet plays a foundational role—eating a diverse, plant-rich diet provides prebiotic fibres that act as "food" for beneficial bacteria, helping them thrive once again.
For a more targeted approach, some individuals may consider probiotic supplements as a convenient option alongside dietary strategies. Certain formulations may help support the restoration of microbial balance, particularly during periods when the gut is more vulnerable.
Ultimately, supporting the gut microbiome is not just about a single intervention, but about proactively maintaining a healthy and sustainable lifestyle. By combining a mindful diet with appropriate probiotic support, it may be possible to better support gut health during and after a course of treatment.
References:
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Campbell D. Number of meningitis cases linked to Kent outbreak rises to 27. The Guardian. 2026 Mar 19.
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Korpela K, de Vos WM. Antibiotic use and impact on gut microbiota composition. J Pediatr Gastroenterol Nutr. 2016;63(1):15-20.
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Francino MP. Antibiotics and the human gut microbiome: dysbioses and accumulation of resistances. Front Microbiol. 2016;6:1543.
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Zmora N, Suez J, Elinav E. You are what you eat: diet, health and the gut microbiota. Nat Rev Gastroenterol Hepatol. 2019;16(1):35-56.
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Dethlefsen L, Relman DA. Incomplete recovery and individualised responses of the human distal gut microbiota to repeated antibiotic perturbation. Proc Natl Acad Sci U S A. 2011;108(Suppl 1):4554-61.
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Pittayanon R, Lau JT, Yuan Y, et al. Gut microbiota in patients with irritable bowel syndrome: a systematic review. Gastroenterology. 2019;157(1):97-108.
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Goodman C, Keating G, Georgousopoulou E, Hespe C, Levett K. Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open. 2021;11(8):e043054. doi:10.1136/bmjopen-2020-043054.
