Sugar may worsen antibiotic-induced gut dysbiosis

The effect was most apparent with added sugars and formulated nutritional drinks, including sports drinks and nutritional shakes.

By
Andrea Surnit
October 7, 2026
5 min

MDSpire News

Overview

In a prospective observational study of adults undergoing allogeneic hematopoietic cell transplantation (HCT), higher sweets or sugar intake during broad-spectrum antibiotic exposure was associated with lower gut microbiome alpha-diversity and greater Enterococcus faecium abundance. In mice, sucrose increased antibiotic-associated enterococcal expansion, while sucrose alone did not increase enterococcal burden. The human findings are observational; the reported mortality association could partly reflect lower overall food intake.

Background

Broad-spectrum antibiotics can disrupt the intestinal microbiome, including reducing microbial diversity. In allogeneic HCT, lower microbiota diversity and Enterococcus domination have been associated with adverse outcomes, including mortality and bloodstream infection. Dietary intake may influence gut microbial composition, but this study examined associations and does not establish that sugar causes microbiome changes in patients. The findings concern a specific, medically complex transplant population and do not establish dietary guidance for other groups.

Data Highlights

Study component	Reported data	Finding
Human cohort	173 adults undergoing allogeneic HCT; 9,419 meals recorded; primary Bayesian analysis included 1,009 stool samples from 158 patients	All patients received at least one antibiotic during dietary monitoring; 138 (80%) transitioned from prophylactic therapy to broad-spectrum antibiotics.
Alpha-diversity and sweets	For each additional 100 g of sweets, measured by dehydrated food weight	During broad-spectrum antibiotic exposure, the model predicted an additional 24% decrease in mean alpha-diversity relative to samples without preceding broad-spectrum antibiotic exposure.
Alpha-diversity and sugar	For each additional 100 g of sugar consumed during broad-spectrum antibiotic exposure	Associated with a further 21% decrease in mean alpha-diversity.
Mortality analysis	Patients with above-median sugar intake	Each additional day of broad-spectrum antibiotic exposure was associated with a 12% higher hazard of mortality; the corresponding association was not statistically significant among patients with below-median sugar intake.
Mouse experiment	After biapenem, enterococcal expansion peaked on day 3 and largely resolved by day 6	Sucrose supplementation increased expansion 16.3-fold on day 3 and 33.4-fold on day 6 versus antibiotic exposure without sucrose. Sucrose did not increase enterococcal burden without antibiotic exposure.

Key Findings

Broad-spectrum antibiotic exposure in the preceding 2 days was associated with lower microbiome alpha-diversity in the human cohort.
Sweets intake alone was not associated with alpha-diversity; higher intake during broad-spectrum antibiotic exposure was associated with a greater decrease.
Dietary analyses implicated formulated nutritional beverages, including sports drinks and nutritional shakes, and added rather than naturally occurring sugars.
Higher sweets intake following broad-spectrum antibiotic exposure was linked to increased Enterococcus faecium abundance; Enterococcus had the strongest inverse relationship with alpha-diversity among the genera examined.
Among patients with above-median sugar intake, each additional day of broad-spectrum antibiotic exposure was associated with a 12% higher mortality hazard. The authors noted that this association could partly reflect reduced overall food intake rather than sugar itself.
In mice, sucrose increased biapenem-associated enterococcal expansion, and the effect persisted under fiber-free dietary conditions. Sucrose did not increase enterococcal burden in mice that did not receive antibiotics.

Clinical Implications

The study reports observational associations in adults undergoing allogeneic HCT and does not establish that reducing sugar intake prevents dysbiosis or improves clinical outcomes. Its findings do not establish a dietary restriction or change to antibiotic management; the mortality association may be confounded by overall food intake.

Conclusion

Higher sugar or sweets intake during broad-spectrum antibiotic exposure was associated with lower microbiome alpha-diversity and greater Enterococcus faecium abundance in the HCT cohort. In mice, sucrose increased antibiotic-associated enterococcal expansion. The human findings are observational, from a single-center study, and the mortality association could partly reflect reduced overall food intake.