Sweet drinks, antibiotics a deadly mix, study finds

When patients lose their appetite, it is common to encourage them to drink sweet or nutritional beverages instead of eating a full meal. Antibiotics, however, do not only kill disease-causing bacteria — they also wipe out many of the beneficial microbes living in the gut, disrupting the intestinal microbiome.

A new study has found that patients who consumed more sugary foods and drinks while on antibiotics experienced a sharper decline in gut bacterial diversity and a greater proliferation of Enterococcus, a pathogenic bacterium.

Researchers Jonathan Peled of Memorial Sloan Kettering Cancer Center and Jonas Schluter of NYU Langone Health published the findings in the 2026 issue of Nature, tracking dietary intake and gut microbiome changes in blood cancer patients who had undergone hematopoietic stem cell transplantation.

Allogeneic hematopoietic stem cell transplantation is a treatment in which blood cancer patients receive stem cells — the cells that produce blood — from a donor. Before the transplant, patients undergo intensive chemotherapy, which often causes mouth and throat sores, nausea and loss of appetite, making it difficult to eat normally.

During this period, patients frequently receive antibiotics to prevent or treat infections. This reduces the diversity of gut bacteria and allows Enterococcus to proliferate — changes associated with poor outcomes, including death.

The research team recorded and analyzed 9,419 meals consumed by 173 patients who underwent stem cell transplantation between 2017 and 2022. From 158 of those patients, the team collected 1,009 stool samples to analyze gut bacterial composition.

Gut bacterial diversity measures how many different species of bacteria live in the intestine and how evenly they are distributed.

The amount of sugar, sweet foods and sweet beverages a patient consumed was not, on its own, associated with gut bacterial diversity. However, among patients receiving antibiotics, each additional 100 grams of sugary food consumed per day was estimated to reduce gut bacterial diversity by 24.1 percent more than in patients not on antibiotics.

To put that in perspective, a 355-milliliter can of cola contains about 39 grams of sugar — meaning the effect was equivalent to drinking about 2.6 additional cans per day.

The research team said the findings were unexpected, given that high-sugar nutritional supplements are commonly recommended for stem cell transplant patients.

Given that disruption of the gut microbiome is linked to poor post-transplant outcomes, the research team examined whether patients who consumed more sugar faced a greater risk of death the longer they remained on antibiotics.

Among patients who consumed relatively more sugar, each additional day on antibiotics was associated with a 12 percent increase in mortality risk. Among those who consumed relatively less sugar, no clear association was found between the duration of antibiotic use and mortality risk.

The team also investigated the relationship between sugar and antibiotics through mouse experiments. A single antibiotic injection caused Enterococcus levels in the gut to increase 100- to 1,000-fold. The elevated counts peaked on the third day and largely returned to baseline by the sixth day.

Among mice that received antibiotics, those fed sugar mixed into their food had 16.3 times more Enterococcus on the third day and 33.4 times more on the sixth day compared with mice that received no sugar. Mice fed only sugar without antibiotics showed no increase in Enterococcus. The effect also occurred when sugar was replaced with glucose, fructose or fruit.

The research team said sugar may have directly promoted Enterococcus growth or impaired the function of other gut bacteria that normally suppress it.

However, the team acknowledged a limitation: patients were already in poor condition before the study, which may have confounded the results. In the paper, the researchers said that "limiting sugar intake during antibiotic treatment may help reduce microbiome disruption."

DOI: 10.1038/s41586-026-11077-3

A. Dai, A. Ballweg, W. Jogia, M. Rangesa, P.A. Adintori, M. Baichoo, T. Funnell, T. Fei, N.R. Waters, A. Swartz, S. Sahu, B. Gipson, S.S. Raj, E. Hayase, Z. Pierce, K. Wu, N. Smith, J. Neuberger, A. Warren, M. Burgos da Silva, O. Miltiadous, C. Zuanelli Brambilla, M. Lubin Buchan, T.K. Peets, A. Gradissimo, L.A. Amoretti, C. Duan, C. Zhang, F. Matheis, A.P. Sullivan, J.B. Slingerland, A.G. Clurman, D.G. Brereton, P.A. Giardina, A.L.C. Gomes, A.J. Johnson, D. Knights, R.R. Jenq, K.A. Markey, M.-A. Perales, S.A. Giralt, M.R.M. van den Brink, J. Schluter, & J.U. Peled, Sugar-rich foods exacerbate antibiotic-induced microbiome disruption, Nature (2026).