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A study published in Nature found that higher sugar intake around antibiotic treatment was associated with a steeper decline in gut bacterial diversity among hospitalized blood cancer patients. The researchers also found increases in Enterococcus faecium in people and mice, but say clinical trials are needed before concluding that reducing sugar improves patient outcomes.
Researchers reported that higher sugar intake around antibiotic treatment was associated with greater loss of gut bacterial diversity in a study of 173 hospitalized blood cancer patients, raising the possibility that diet can affect the drugs’ impact on the microbiome. The Nature study also found increases in the potentially harmful bacterium Enterococcus faecium, but it did not establish that reducing sugar improves patients’ health outcomes.
The team from NYU Langone Health, City of Hope and Memorial Sloan Kettering Cancer Center analyzed 9,419 recorded meals and tracked patients’ gut microbiomes during hospitalization. For every additional 100 grams of sugar consumed in the 48 hours before treatment, researchers observed an additional 21% decline in alpha diversity, a measure of the variety of bacterial species in the gut. This is an association reported by the study, not proof that sugar alone caused the decline.
The researchers also reported that sugary diets combined with antibiotic treatment were associated with increases in Enterococcus faecium, a species linked to infections that can be difficult to treat. In a separate mouse experiment, animals given the antibiotic biapenem while eating dietary sucrose had a 16.3-fold increase in gut Enterococcus by day three and a 33.4-fold increase by day six. These animal results do not show that the same size of effect occurs in people.
Diet was recorded at each meal and microbiome samples were collected daily, allowing the team to track changes during treatment. The study’s authors suggest that sugar could help bacteria that survive antibiotics expand, but they said the precise mechanism in patients remains unknown. They identify reducing simple sugars as a possibility to test, rather than an established treatment recommendation.
Diet May Shape Antibiotic Effects
Antibiotics can affect bacteria that cause illness as well as beneficial members of the gut community. A loss of microbial diversity may leave space for other species to grow. The new findings add diet to the factors researchers are examining when studying how the microbiome changes during antibiotic treatment, particularly in patients already facing intensive cancer care.
The population studied is medically vulnerable: patients with blood cancers may receive antibiotics alongside chemotherapy or stem cell transplantation and can spend weeks in hospital. Study co-author Jonathan Peled said microbiome injury in these patients is associated with worse outcomes, including infections and higher overall mortality. The study did not test whether sugar reduction changes those outcomes, so it cannot show that a dietary adjustment prevents infection or improves survival.
For readers taking antibiotics outside the hospital, the findings do not support changing a prescribed course or treating sugar restriction as a substitute for medical care. The direct evidence comes from hospitalized cancer patients and animal experiments. Whether the association applies broadly, and whether changing diet makes a meaningful difference, still needs testing.
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Why Researchers Tracked Cancer Patients
The team focused on people with blood cancers because they often receive antibiotics and can be monitored closely during hospitalization. Their meals and microbiome samples were recorded repeatedly, giving researchers a way to compare recent food intake with bacterial changes over time. This intensive approach produced thousands of meal records, but the setting also means the results may not describe people receiving routine outpatient antibiotics.
Antibiotic treatment can reduce the variety of gut bacteria. Researchers say a diverse microbiome can help resist the expansion of potentially harmful species. In patients whose microbial communities are disrupted during treatment, Enterococcus faecium may gain an advantage. The study examined how sugar intake might relate to that process; it did not establish the biological pathway or show that sugar is the only factor involved.
The findings were published online in Nature on September 30, 2026. The researchers’ account includes both observations from patients and a controlled mouse experiment. Those two forms of evidence support further investigation, but neither amounts to a clinical trial of a low-sugar diet during antibiotic treatment.
“The healthy diversity of the gut microbiome can have important implications for outcomes.”
— Marcel van den Brink, study co-senior author and City of Hope chief physician executive
How Much Sugar Changes Risk
The patient findings show an association between sugar intake and changes in microbiome diversity; they do not establish that sugar caused those changes. The supplied study account does not provide evidence that reducing sugar during antibiotic treatment prevents infection, speeds recovery or improves survival. It also does not establish a specific amount of sugar that patients should eat or avoid.
The mechanism remains unsettled. The researchers say sugar might help antibiotic-resistant or surviving bacteria expand, weaken competing bacteria, or affect the microbiome in another way. The study involved hospitalized people with blood cancers, so it is unclear how directly the results apply to other patients, different antibiotics or everyday diets. The mouse results offer supporting experimental evidence, not a human treatment test.
Clinical Trials Are the Next Test
The researchers say the next step is to design clinical trials testing whether short-term dietary changes during or after antibiotic treatment affect microbiome recovery and patient outcomes. Such trials would need to determine whether reducing simple sugars changes bacterial diversity or Enterococcus levels, and whether any microbiome changes translate into fewer infections or other measurable benefits.
Until those results are available, the study supports further research rather than a proven dietary prescription. Patients should follow instructions from their health care team about antibiotics and nutrition, especially during cancer treatment or other complex care. The report does not recommend stopping, delaying or changing prescribed antibiotics.
Key Questions
Does this study prove sugar makes antibiotics damage the gut?
No. The study found an association between higher sugar intake and a greater decline in gut bacterial diversity among hospitalized blood cancer patients. It does not prove that sugar caused the change.
Should people cut sugar while taking antibiotics?
The findings do not establish a dietary prescription or show that cutting sugar improves health outcomes. The authors say clinical trials are needed. Do not change prescribed antibiotic treatment based on this study; ask a health care professional about individual diet questions.
What does the 21% figure describe?
For each additional 100 grams of sugar consumed in the 48 hours before treatment, researchers observed an additional 21% decline in alpha diversity, a measure of the variety of gut bacterial species. It is a study association, not a proven effect of a sugar intervention.
Were the Enterococcus results found in people?
The researchers reported that sugary diets combined with antibiotic treatment were associated with increases in Enterococcus faecium among patients. They also saw much larger increases in gut Enterococcus in mice given biapenem and sucrose; those animal measurements should not be treated as estimates of the effect in people.
Source: rss
