Study Links Sugar Intake During Antibiotics to Greater Gut Damage in Transplant Patients

A study published in the journal Nature has found that eating sugar-rich foods while taking antibiotics may worsen disruption to the gut microbiome in patients undergoing blood stem-cell transplantation. Researchers analysed thousands of meals and stool samples and found that higher sugar intake during antibiotic exposure was associated with a greater loss of bacterial diversity and increased growth of Enterococcus, a bacterium that can cause serious infections in vulnerable patients.

The findings, published on September 30, 2026, offer new evidence that diet may influence how antibiotics affect the gut’s microbial ecosystem. The research team also tested the relationship in mice, where adding sucrose increased and prolonged antibiotic-associated Enterococcus growth. However, the human study focused on hospitalised transplant patients receiving intensive treatment, so the findings should not be interpreted as proof that everyone taking antibiotics needs to eliminate sugar from their diet.

Key Takeaways

• Study published: The research appeared in Nature on September 30, 2026.
• Participants: Researchers followed 173 patients undergoing blood stem-cell transplantation.
• Dietary data: The team tracked 9,419 meals and analysed 1,009 stool samples from 158 patients.
• Main finding: Higher consumption of sweets and sugar-rich foods during antibiotic exposure was associated with lower gut bacterial diversity.
• Potentially harmful bacteria: Researchers observed greater expansion of Enterococcus, including bacteria associated with serious hospital-acquired infections.
• Animal experiments: Mouse studies supported the link between sucrose and prolonged antibiotic-related bacterial expansion.
• Important limitation: Further research is needed before applying the findings broadly to otherwise healthy people taking antibiotics.

Why the Gut Microbiome Matters During Antibiotic Treatment

The gut microbiome is the community of microorganisms living in the digestive tract. It includes many bacterial species that contribute to digestion, metabolism and immune function.

A diverse microbial community can help maintain an ecological balance in the gut. Different microorganisms compete for nutrients and space, which can make it more difficult for particular harmful organisms to dominate.

Antibiotics are essential medicines for treating bacterial infections, but they can also affect beneficial bacteria. Broad-spectrum antibiotics are particularly capable of disrupting the gut microbiome because they target a wide range of bacteria rather than a single organism.

When this microbial balance is disturbed, certain bacteria may gain an advantage. In vulnerable patients, this can create conditions in which opportunistic pathogens expand and potentially contribute to serious complications.

The research team investigated whether dietary sugar could influence this process. Their findings suggest that the combination of antibiotics and sugar-rich food intake may be more disruptive to the gut microbiome than antibiotic exposure alone in the patient population studied.

How Researchers Investigated Sugar and Gut Bacteria

The research involved patients with blood cancers who were hospitalised for haematopoietic cell transplantation, a procedure that replaces blood-forming stem cells. These patients often undergo intensive treatment that weakens their immune systems and may require antibiotics to prevent or treat infections.

Because patients remain in the hospital for extended periods, researchers were able to collect unusually detailed information about food consumption and medication exposure.

The team tracked 9,419 meals eaten by 173 patients. Researchers recorded what patients consumed and used nutritional information about the hospital’s food to estimate dietary intake.

They also collected more than 1,000 stool samples to monitor changes in the gut microbiome. The main analysis of bacterial diversity used longitudinal samples from 158 patients.

This approach allowed the researchers to examine how dietary intake and antibiotic exposure were associated with subsequent changes in gut bacteria.

The study is notable for the scale and detail of its dietary records. Food intake is often difficult to measure accurately because people may forget what they ate or underestimate portion sizes. Recording hospital meals alongside nutritional data helped the researchers reduce some of those measurement problems.

Nevertheless, the study was observational in humans. Even when statistical models account for known factors, an association does not automatically prove that one factor directly causes another.

What the Study Found About Sugar and Microbiome Diversity

The researchers found that consumption of sweets, sugars and certain beverages during antibiotic exposure was associated with a greater reduction in gut bacterial diversity.

The analysis estimated that, for every additional 100 grams of sugar-rich foods and beverages consumed in the relevant period, microbiome alpha diversity was approximately 24% lower in the antibiotic-exposed samples compared with samples without the preceding antibiotic exposure, according to the model.

Alpha diversity is a measure of the variety of microorganisms within a particular sample. A lower value indicates that the microbial community has become less diverse, although diversity alone does not fully determine whether a microbiome is healthy.

The 100-gram figure is a statistical comparison from the study, not a recommended dietary threshold or a prediction that every person consuming that amount will experience the same change.

The researchers also found that sugar-rich food intake was associated with greater expansion of Enterococcus. This suggests that the dietary environment may influence which organisms become more prominent after antibiotics disturb the gut’s existing microbial community.

The findings do not mean that all sugar is harmful to every person taking antibiotics. They indicate that sugar intake may act as a modifiable factor in an already vulnerable gut ecosystem, particularly among patients receiving intensive treatment.

Why Enterococcus Growth Is a Concern

Enterococcus bacteria can normally exist in the human intestinal tract without causing disease. However, some species, including Enterococcus faecium, can become dangerous when they expand excessively or enter parts of the body where they should not be present.

In hospital settings, certain strains can be resistant to multiple antibiotics, making infections difficult to treat. Bloodstream infections caused by these bacteria can be particularly serious for patients whose immune systems have been weakened by cancer treatment or transplantation.

Previous research has linked the loss of gut microbial diversity and the dominance of Enterococcus with adverse outcomes in transplant patients.

The new study adds a possible dietary dimension to this problem. If sugar-rich foods help certain bacteria expand after antibiotics disrupt the microbiome, dietary choices could potentially influence the balance between beneficial and harmful microorganisms.

However, the researchers did not establish that the observed dietary association directly caused additional bloodstream infections in the participants. The study primarily examined microbiome changes, and further clinical research is needed to determine whether dietary interventions improve infection rates or other patient outcomes.

Mouse Experiments Support the Findings

The researchers also conducted experiments in mice to test whether sucrose could influence antibiotic-related changes in gut bacteria.

The animal experiments supported the human observations: adding sucrose increased and prolonged antibiotic-induced expansion of Enterococcus. This provides additional evidence that the relationship may involve biological mechanisms rather than being explained entirely by differences between patients.

The experiments do not, however, prove that the same effect will occur to the same extent in humans outside the transplant setting.

Animal studies can help researchers investigate possible mechanisms under controlled conditions, but human diets, microbiomes, illnesses and medication regimens are more complex.

The researchers also noted that further work is needed to understand precisely how sugar affects the gut ecosystem. The effect could involve changes in nutrient availability for surviving bacteria, competition between microbial species or other interactions within the gut.

Could Sugary Drinks and Nutritional Shakes Be Part of the Problem?

One surprising aspect of the findings is their relevance to foods and drinks sometimes offered to people who are unwell.

Smoothies, sports drinks and nutritional shakes can provide fluids, calories and nutrients to patients who struggle to eat regular meals. In cancer care, these products may be used to help people maintain their energy intake during demanding treatment.

Some of these products also contain substantial amounts of added sugar or other simple sugars. The study suggests that, in transplant patients receiving antibiotics, sugar-rich products may be associated with greater disruption to the gut microbiome.

This creates a clinical question rather than a simple instruction to avoid all nutritional drinks. Patients undergoing transplantation may have high nutritional needs, and inadequate food intake can create its own risks.

A drink that provides necessary calories or hydration may serve a different purpose from a sugary soft drink consumed for enjoyment. The research does not establish that all nutritional supplements should be removed from transplant patients’ diets.

Instead, it raises the possibility that healthcare teams may need to consider sugar content when selecting nutritional support for particular patients. That approach would need to balance microbiome considerations against calorie requirements, treatment side effects and individual nutritional needs.

Does This Mean Everyone Taking Antibiotics Should Avoid Sugar?

Not yet. The study does not provide enough evidence to recommend a universal sugar-free diet for all people taking antibiotics.

The participants were hospitalised patients undergoing blood stem-cell transplantation. Their treatment, immune status and exposure to broad-spectrum antibiotics differ substantially from those of otherwise healthy people taking a short course of antibiotics for a common infection.

The researchers themselves have emphasised the need for further studies to determine whether reducing sugar intake leads to better clinical outcomes.

For people taking antibiotics outside a hospital, the findings support a reasonable distinction between limiting excessive added sugar and eliminating all sugar-containing foods. Whole fruits, dairy products and medically recommended nutritional supplements can provide important nutrients, and the study does not establish that these foods should automatically be avoided.

Patients should continue taking prescribed antibiotics as directed and should not change their treatment because of this research. People receiving cancer treatment, stem-cell transplants or other intensive medical care should discuss dietary changes with their clinical team, particularly if they have been advised to follow a specialised nutrition plan.

What Researchers Need to Investigate Next

The next step is to test whether deliberately reducing sugar-rich foods during antibiotic treatment can protect the microbiome and improve health outcomes.

A prospective clinical trial could compare dietary approaches among suitable patients while monitoring microbial diversity, bacterial expansion, infections and nutritional status. Such a trial would help determine whether the association found in the observational study can be translated into an effective intervention.

Researchers also need to investigate which foods contribute most strongly to the effect and whether the findings apply to different antibiotic classes, patient groups and treatment settings.

Another question is whether the timing of sugar intake matters. The study examined dietary consumption around antibiotic exposure, but additional research could clarify how long dietary changes would need to be maintained and whether they have lasting effects.

Ultimately, the goal is not simply to reduce one dietary ingredient. It is to identify practical ways to protect beneficial microorganisms without compromising nutrition or the treatment of serious infections.

The Bigger Picture

The study highlights how diet and medication can interact in ways that are not always obvious. Antibiotics can disrupt the gut microbiome, and the researchers found that sugar-rich food intake was associated with an even greater loss of microbial diversity among patients undergoing blood stem-cell transplantation. The mouse experiments strengthened the biological case for further investigation.

However, the findings remain specific to a medically vulnerable population and do not establish a universal rule for everyone taking antibiotics. The next challenge is to determine whether carefully designed dietary changes can reduce microbiome damage and improve clinical outcomes while ensuring patients continue to receive adequate nutrition.

Looking Ahead

Further clinical trials will be needed to determine whether limiting simple sugars during antibiotic treatment can meaningfully protect the gut microbiome in transplant patients and other groups. Researchers will need to assess both potential benefits and possible nutritional trade-offs before recommending a standard dietary intervention. Until then, the findings should be viewed as an important research lead rather than definitive dietary guidance.

For patients and clinicians, the study reinforces the importance of considering diet alongside medication, especially during intensive medical treatment. It also illustrates how detailed monitoring of food intake and microbial changes can reveal potential interactions that deserve closer study. Future evidence will determine whether sugar reduction becomes part of a formal strategy to preserve gut health during antibiotic therapy.

Frequently Asked Questions

1. What did the study find about sugar and antibiotics?

The study found that higher consumption of sugar-rich foods during antibiotic exposure was associated with lower gut bacterial diversity and greater expansion of Enterococcus in patients undergoing blood stem-cell transplantation.

2. How many people were involved in the research?

Researchers tracked the diets of 173 patients and analysed 1,009 stool samples from 158 patients.

3. Does the study prove that sugar causes gut damage in everyone taking antibiotics?

No. The human findings were observational and came from hospitalised transplant patients. Further research is needed before the results can be generalised to everyone taking antibiotics.

4. Why is Enterococcus potentially dangerous?

Some Enterococcus species can cause serious infections, particularly in vulnerable hospital patients. Certain strains are resistant to multiple antibiotics, making infections more difficult to treat.

5. Should people stop eating sugar while taking antibiotics?

The study does not establish a universal requirement to avoid sugar. Limiting excessive added sugar may be reasonable for general health, but people should follow their clinician’s dietary advice, especially during cancer treatment or transplantation.

6. What happens next?

Researchers need clinical trials to determine whether reducing sugar-rich foods during antibiotic treatment protects the microbiome and improves outcomes such as infection rates, without compromising nutrition.

Source note, 17 October 2026: Nature research paper: observational findings in hospitalised transplant patients and separate mouse experiments.