Sugar during antibiotic treatment harms gut flora, study shows

A clinical study published in the journal Nature, cited by the EFE news agency, shows that avoiding foods and drinks high in sugar during a course of antibiotics could protect the gut flora and, by extension, the patient's general health.

Antibiotics are effective against infections, but they also affect the "good" bacteria in the gut, leaving room for harmful bacteria to thrive.

How the study was conducted

Researchers from several medical centres in the United States monitored the diets of leukaemia patients admitted for an intensive treatment known as "allogeneic haematopoietic cell transplantation". These patients received intensive chemotherapy, sometimes combined with radiotherapy, to suppress the immune system prior to the stem cell transplant.

All patients received at least one antibiotic during their hospital stay, and in 80% of cases it was a "broad-spectrum" antibiotic, with a powerful effect on the intestinal microflora.

The team analysed 9,419 meals consumed by 173 hospitalised patients and compiled a profile of intestinal bacterial diversity based on stool samples collected from 158 of them. Each patient completed a questionnaire about the quantity of food and drinks consumed, and the catering staff provided nutritional information for every dish served. In total, the researchers recorded data on more than 40,000 food items, tracking an average of 128 meals per patient over a period spanning 12 days before to 49 days after the transplant.

What the researchers discovered

Patients who consumed more sweets or other sources of sugar whilst undergoing antibiotic treatment were more likely to lose diversity in their gut flora, as aggressive bacteria took the place of other strains.

One of the infections whose risk increased significantly with sugar consumption is that caused by the bacterium Enterococcus faecium. According to the researchers, when this bacterium dominates the microflora, patients who have undergone a transplant face a greater risk of bloodstream infections and other potentially fatal complications.

The study showed an additional 21% decrease in alpha diversity — a measure of the variety of beneficial bacterial species in the gut — for every 100 grams of sugar consumed in the 48 hours prior to treatment. Furthermore, the combination of sugar-rich foods and broad-spectrum antibiotics amplified the negative effects on the microflora.

What the study's authors say

"These findings will be essential for developing new treatment strategies for cancer patients and, potentially, for other people taking antibiotics," said Marcel van den Brink, president of City of Hope hospital in Los Angeles, one of the study's authors.

According to him, the results "reinforce the idea that diet exerts a powerful influence on the microflora and represents one of the most practical ways in which hospitals can support recovery during treatment".

Van den Brink highlighted that many sweetened foods and drinks, such as shakes and juices, have a high sugar content — "an aspect we will need to evaluate when prescribing antibiotics," he noted, as quoted in a press release.

The study's authors recommend that patients discuss antibiotic choices with their doctors, so that treatment remains equally effective in controlling infections whilst having as little impact as possible on gut flora. "Antibiotic stewardship goes beyond simply preventing resistance to them," Van den Brink emphasised.