Nature: Sugar During Antibiotic Treatment Disrupts the Gut Microbiome More Severely

The researchers analyzed nearly 9,500 meals consumed by patients who had undergone hematopoietic cell transplantation. They found that high sugar intake during antibiotic treatment was associated with a more pronounced loss of gut bacterial diversity.

The researchers examined the diets of 173 patients with blood disorders who underwent allogeneic hematopoietic cell transplantation. All received antibiotics, and their food intake was carefully recorded during their hospital stays. In total, the scientists analyzed 9,419 meals and compared dietary data with the results of stool sample analyses.

Gut bacterial diversity predictably declined after transplantation. The disruption to the microbiome was particularly pronounced in patients receiving broad-spectrum antibiotics. However, the researchers found that the amount of sugar in the diet could also influence this process.

Eating sugary foods alone was not associated with a substantial reduction in bacterial diversity. But when sugar consumption coincided with antibiotic use, the association became apparent. According to the researchers' calculations, every additional 100 grams of sugary foods was associated with an approximately 24% further reduction in gut microbiome diversity.

One particularly interesting finding concerned Enterococcus faecium, a bacterium that can cause severe infections and is resistant to some antibiotics. After antibiotic treatment, higher sugar intake was associated with an increase in the bacterium's share of the gut microbial community.

The findings from human observations received additional support from experiments in mice. After receiving antibiotics, the animals were given sucrose. The number of enterococci in their intestines increased sharply compared with mice that received antibiotics without additional sugar. By day three, the number was approximately 16 times higher, and by day six, it was more than 33 times higher. Sugar alone, without prior antibiotic exposure, did not produce this effect.

The researchers suggest that antibiotics eliminate some competing bacteria, creating space for microorganisms capable of using available nutrients. Sugars may further promote the growth of certain potentially harmful bacteria or alter the gut's response. However, the exact mechanism has yet to be established.

The study also identified a possible link between diet and treatment outcomes. Among patients who consumed more sugar, each additional day of broad-spectrum antibiotic treatment was associated with an increased risk of death. However, this observation does not prove that sugary foods caused the poorer outcomes: the human study was observational, and transplant recipients are seriously ill and have multiple other risk factors.