Medication is shown to kill essential gut bacteria and can negatively affect performance

Taking a course of antibiotics might seem the fastest route to overcoming an infection, but researchers warn that the effects could backfire for athletes.

Results of a study at the University of California, published in the journal Behavioural Processes, showed that, by killing essential gut bacteria, antibiotics potentially harm athletes’ motivation and endurance. In the study on laboratory animals, some bred for high levels of running, and others that weren’t, faecal samples revealed that gut bacteria were reduced in both groups after 10 days of taking antibiotics. 

Although none of the animals exhibited any other obvious side effects from the medication, the distance run by the athletic animals reduced by 21 per cent – something the scientists attributed to microbiome damage. Even 12 days after finishing the antibiotics, performance had not returned to normal in the running animals. 

The findings are relevant for elite athletes, says Monica McNamara – an evolutionary biology student and the lead author – and the effects of a ravaged gut microbiome are comparable to an injury. Partly, the downturn in performance is a result of a reduced ability of the microbiome to transform carbohydrates into chemicals that affect muscle activity.

“Metabolic end products from bacteria in the gut can be reabsorbed and used as fuel,” says co-author Theodore Garland, an evolutionary physiologist. “Fewer good bacteria means less available fuel.”