Eating sugary foods while taking antibiotics significantly worsens damage to your gut bacteria, according to a 2026 study of 173 hospitalized patients published in Nature. Researchers found that patients who consumed sweets during antibiotic treatment had lower diversity of beneficial bacteria and greater growth of harmful Enterococcus bacteria. Gram Research analysis shows that avoiding sugar during antibiotic courses may help protect your gut microbiome and support faster recovery.
When you take antibiotics, they kill both harmful and helpful bacteria in your gut. A new study of 173 hospitalized patients found that eating sugary foods while taking antibiotics makes this damage much worse. Researchers tracked nearly 9,500 meals and discovered that patients who ate sweets during antibiotic treatment had fewer types of healthy gut bacteria and more harmful bacteria called Enterococcus. According to Gram Research analysis, this suggests a simple dietary change could help protect your gut health during antibiotic treatment. The findings were confirmed in mice studies, showing the effect is real and consistent.
Key Statistics
A 2026 study of 173 hospitalized patients published in Nature found that eating sugary foods during antibiotic treatment predicted significantly worse gut bacteria disruption, including reduced bacterial diversity and increased harmful Enterococcus expansion.
Mouse experiments confirmed that sucrose supplementation during antibiotic exposure increased and prolonged the expansion of harmful Enterococcus bacteria compared to antibiotics alone.
Researchers tracked 9,419 individual meals consumed by 173 patients and used advanced statistical analysis to show that simple sugar intake during antibiotic exposure was directly linked to exacerbated microbial dysbiosis.
The Quick Take
- What they studied: Whether eating sugary foods makes antibiotic damage to gut bacteria worse or better
- Who participated: 173 patients in the hospital receiving stem cell transplants who were taking antibiotics, plus mice in laboratory experiments
- Key finding: Patients who ate sugary foods while taking antibiotics had significantly worse gut bacteria damage, with lower diversity of good bacteria and more growth of harmful Enterococcus bacteria
- What it means for you: If you’re taking antibiotics, limiting sugary foods and sweets during treatment may help protect your beneficial gut bacteria. This is especially important during or after serious medical treatments, though more research is needed to confirm benefits in everyday situations
The Research Details
Researchers studied 173 patients who were hospitalized and receiving antibiotics as part of stem cell transplant treatment. They carefully tracked every meal these patients ate, recording nearly 9,500 individual meals over time. Scientists then analyzed samples of the patients’ gut bacteria at different time points to see how the bacteria changed. They used advanced statistical methods to figure out which foods were connected to the biggest changes in gut bacteria. To confirm their findings, the researchers also did experiments with mice, giving some mice antibiotics plus sugar and others just antibiotics, then measuring how their gut bacteria changed.
This research design is powerful because it tracks real patients in real situations rather than just testing in a lab. By recording exactly what people ate and then measuring their gut bacteria, researchers could see direct connections between specific foods and bacterial changes. The mouse experiments helped prove that sugar actually causes the problem, not just that people who eat sugar happen to have worse outcomes for other reasons.
This study has several strengths: it involved a large number of patients (173), tracked detailed meal information (9,419 meals), and used advanced statistical analysis. The findings were confirmed in animal experiments. However, the patients studied were in hospitals receiving special medical treatment, so results may not apply to people taking antibiotics in everyday situations. The study was published in Nature, one of the world’s most respected scientific journals
What the Results Show
The main finding was clear: patients who ate sugary foods and sweets while taking antibiotics experienced much worse damage to their gut bacteria. Specifically, their gut bacteria diversity dropped more sharply, meaning they lost more types of beneficial bacteria. At the same time, a harmful bacterium called Enterococcus grew much more aggressively in patients who consumed sugar during antibiotic treatment. In patients who avoided sugary foods, the antibiotic damage to their gut bacteria was less severe. The mouse experiments showed the same pattern: mice given antibiotics plus sugar had much larger populations of Enterococcus bacteria compared to mice given antibiotics alone.
The research also showed that the harmful effects of sugar lasted longer. In mice, the Enterococcus expansion was not only bigger but also persisted for a longer time when sugar was added to the diet. This suggests that sugar doesn’t just make the initial damage worse, but also slows down recovery of normal gut bacteria. The study tracked bacteria over time and found these patterns held up consistently across different patients and time periods.
Previous research has shown that diet affects gut bacteria composition, but this study is one of the first to carefully examine what happens during extreme stress to the microbiome, such as during antibiotic treatment. Earlier studies suggested that simple sugars might feed harmful bacteria, but this research provides direct evidence in humans that this actually happens during antibiotic use. The findings support existing nutritional advice to limit sugar intake during medical treatment, but now with specific evidence about gut bacteria.
The patients in this study were hospitalized and receiving stem cell transplants, which is a very different situation from someone taking antibiotics at home for an infection. Their gut bacteria may have been disrupted by the transplant procedure itself, not just the antibiotics. The study doesn’t tell us whether the same effects would happen in healthy people taking antibiotics for routine infections. Additionally, the study was observational, meaning researchers watched what happened rather than randomly assigning people to eat different diets, so we can’t be completely certain sugar caused the problem rather than something else
The Bottom Line
If you’re taking antibiotics, especially during serious medical treatment, try to limit sugary foods, sweets, and sugary drinks during your course of treatment. This recommendation has strong support from this research. For people taking antibiotics for routine infections, the evidence is less clear, but limiting sugar is still a reasonable precaution. Consider eating whole foods, vegetables, and fiber-rich foods instead, which may help support healthy gut bacteria
This finding is most relevant to people undergoing serious medical treatments like stem cell transplants who are taking antibiotics. It’s also worth considering for anyone taking antibiotics for extended periods. People taking short courses of antibiotics for routine infections should discuss dietary changes with their doctor. Patients with weakened immune systems should pay special attention to this guidance
The effects on gut bacteria happened relatively quickly, within days of starting antibiotics combined with sugar consumption. Recovery of normal gut bacteria typically takes weeks to months after stopping antibiotics, and avoiding sugar during treatment may speed up this recovery process
Frequently Asked Questions
Should I avoid sugar while taking antibiotics?
Research shows that eating sugary foods during antibiotic treatment worsens damage to your gut bacteria. Limiting sugar intake during your antibiotic course may help protect beneficial bacteria and support faster recovery. Discuss specific dietary changes with your doctor, especially if you’re undergoing serious medical treatment.
What happens to gut bacteria when you take antibiotics?
Antibiotics kill bacteria in your gut, including both harmful and helpful types. This disruption, called dysbiosis, reduces the diversity of your gut bacteria. According to this research, eating sugar during antibiotic treatment makes this disruption worse by allowing harmful bacteria like Enterococcus to grow more aggressively.
How long does it take for gut bacteria to recover after antibiotics?
Recovery typically takes weeks to months after stopping antibiotics. This study suggests that avoiding sugar during antibiotic treatment may speed up recovery by preventing excessive growth of harmful bacteria. Individual recovery times vary based on the antibiotic type, treatment duration, and diet.
What should I eat instead of sugary foods during antibiotic treatment?
Choose whole grains, vegetables, fruits, lean proteins, and fiber-rich foods instead. These foods support beneficial gut bacteria. Avoid sugary drinks, desserts, and processed foods high in added sugars. Consider foods like yogurt, kefir, and fermented vegetables that contain beneficial bacteria, but check with your doctor first.
Does this research apply to all antibiotics or just some?
This study examined patients taking various antibiotics during stem cell transplant treatment. The findings likely apply broadly to antibiotic use, but the effect may be strongest during serious medical treatments. More research is needed to confirm whether the same patterns occur with routine antibiotic use for common infections.
Want to Apply This Research?
- Log daily sugar intake in grams and track gut health markers like digestive comfort, energy levels, and bowel regularity during antibiotic courses. Compare weeks with high sugar intake to weeks with low sugar intake
- When prescribed antibiotics, set a reminder to avoid sugary foods and drinks for the duration of treatment. Use the app to plan antibiotic-friendly meals with whole grains, vegetables, and protein sources instead of sweets
- Track antibiotic start and end dates, daily sugar consumption, and digestive symptoms over 4 to 8 weeks. Note any patterns between sugar intake and digestive issues like bloating, constipation, or diarrhea
This research was conducted in hospitalized patients undergoing stem cell transplants and may not apply directly to people taking antibiotics for routine infections. Always consult with your healthcare provider before making dietary changes during antibiotic treatment, especially if you have underlying health conditions or are taking other medications. This information is for educational purposes and should not replace professional medical advice. Individual responses to dietary changes during antibiotic treatment may vary significantly.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.