Here’s a twist nobody puts on the pharmacy label: what you eat while you’re on antibiotics may change how much damage the drugs do to your gut. In a new study of 173 hospitalized cancer patients and more than 9,400 carefully tracked meals, every extra 100 grams of sugar eaten in the two days before a stool sample was linked to roughly a 21% further drop in gut bacterial diversity when patients were on antibiotics.
The research, published September 30, 2026, in Nature, is the clearest look yet at how sugar and antibiotics may team up against your microbiome. It comes with big caveats, though. Here’s what the scientists found, who it applies to, and what you can sensibly do with it.
What the Sugar and Antibiotics Study Found
The study was led by researchers at NYU Langone Health, City of Hope and Memorial Sloan Kettering Cancer Center. They followed adults with blood cancers who were in the hospital for a stem cell (bone marrow) transplant. These patients get antibiotics often, and because they ate only hospital-prepared food, the team knew exactly what was on every plate.
According to the paper in Nature, the researchers tracked 9,419 meals eaten by 173 patients and analyzed 1,009 stool samples from 158 of them. Their statistical model looked at how food groups, antibiotics and clinical factors related to “alpha diversity,” a measure of how many different kinds of bacteria live in the gut.
The key results:
- Sugar alone wasn’t the problem. Eating sweets was not linked to lower diversity on its own. The drop showed up when sugar intake came on top of broad-spectrum antibiotic exposure.
- About 21% more diversity loss per 100 g of sugar. In the macronutrient model, each extra 100 grams of sugars during antibiotic exposure predicted a further 20.6% decrease in diversity. A separate food-group analysis of “sweets” (sugars, sweetened foods and beverages) put the figure at about 24% per 100 grams.
- A bloom of a troublemaker. The sugar-plus-antibiotics combination was tied to expansion of Enterococcus faecium, a gut bacterium linked to hard-to-treat infections.
“Our study, which used more than 9,000 recorded meals, suggests that modifying diet during and after antibiotics, specifically by reducing sweets intake, could help with that,” co-senior author Jonas Schluter, PhD, an assistant professor of microbiology at NYU Langone, said in the NYU Langone announcement.
Why Gut Diversity Matters
Your gut is home to trillions of microbes that help digest food, make certain vitamins and support your immune system. A crowded, varied community is harder for harmful bugs to break into. Scientists call that “colonization resistance.”
That’s why the mix of sugar and antibiotics matters. Antibiotics are lifesavers, but they don’t only hit the germs causing your infection. They also knock out helpful species. When diversity crashes, opportunists that survive the drugs can take over.
Enterococcus is one of those opportunists. It usually lives in the gut quietly, kept in check by competitors. When those competitors are wiped out, it can overgrow. In vulnerable patients, it can even slip into the bloodstream.
“Especially in blood cancer patients, microbiome injury is associated with worse outcomes, including higher overall mortality and infections,” said co-senior author Jonathan Peled, associate director of the Center for Hematological Malignancies at Memorial Sloan Kettering, in the NYU Langone release.
The survival signal (and why it’s modest)
The team also checked whether the sugar-antibiotic combination tracked with survival. Among patients whose sugar intake was above the group median, each additional day of broad-spectrum antibiotic exposure was linked to about a 12% higher mortality risk (hazard ratio 1.12). In patients with below-median sugar intake, that link was not statistically significant.
Peled described it to CNN as “a modest change in their risk profile.” Remember, this is a correlation in a very sick group of patients, not proof that sugar caused any deaths.
The Mouse Experiments: A 33-Fold Jump
To see whether sugar could actually drive the bacterial bloom, the team turned to mice. They gave the animals a broad-spectrum antibiotic called biapenem, with or without added table sugar (sucrose).
The combination drove a 16.3-fold increase in Enterococcus in the gut by day 3 and a 33.4-fold higher burden by day 6, according to NYU Langone. The paper says sucrose both increased and prolonged the antibiotic-driven Enterococcus expansion.
Mouse results suggest the sugar and antibiotics combination isn’t just a coincidence and that sugar may play an active role. But mice aren’t people. And the researchers are careful about the “why.” Study second author William Jogia, a PhD student in Schluter’s lab, said the harmful bacteria that survive antibiotics are “probably” benefiting from dietary sugars they can use to expand. He added that whether sugar directly feeds Enterococcus, weakens its competitors, or works some other way in patients “remains to be seen.”
Big Caveats: Who This Sugar and Antibiotics Research Applies To
Before you clear out your pantry, here’s what this study on sugar and antibiotics can and can’t tell you:
- It’s association, not causation, in humans. The patient data are observational. The study was not a randomized trial that assigned people to low- or high-sugar diets.
- The patients were extremely sick. These were stem cell transplant recipients getting chemotherapy and, often, heavy-duty IV antibiotics. In this group, 80% (138 of 173) were switched to broader-spectrum antibiotics during the study period.
- It hasn’t been tested in healthy people. Nobody yet knows whether a few cookies during a 7-day course of amoxicillin for a sinus infection has any lasting effect.
- The authors say more work is needed. The paper’s abstract says further studies in independent groups are needed to generalize the findings. Peled said an important next step is designing clinical trials to test whether short-term diet changes improve outcomes.
Dr. Anthony Maresso, a Baylor College of Medicine microbiologist who was not involved, told CNN the open question is whether the finding matters for people taking antibiotics outside the hospital.
What You Can Do If You’re Taking Antibiotics
The evidence on sugar and antibiotics is early, but the practical steps below are low-risk and line up with general healthy-eating advice. They are not a substitute for your doctor’s instructions.
1. Take your antibiotics exactly as prescribed
This is the most important rule. Don’t skip doses, stop early, or change your medication because of a diet study. If you have concerns about side effects or your gut, talk to the prescriber.
2. Go easy on sweets during the course
Peled told CNN that because it’s generally a good idea not to overdo sugar anyway, it’s “not unreasonable” to consider limiting it during antibiotic treatment. He stressed the idea is to cut back specifically while you’re on antibiotics, not forever. For context, the American Heart Association recommends no more than about 25 grams of added sugar a day for women and 36 grams for men. That’s well under the 100-gram increments in the study.
3. Lean on whole, fiber-rich foods
Diets rich in plants and fiber are generally linked to a more diverse gut microbiome. Think vegetables, fruit, beans, nuts and whole grains. If you want a reason to load up on grains, our look at whole grains and heart health breaks down how many servings research supports.
4. Be cautious with probiotics
The evidence on probiotics is mixed. The National Center for Complementary and Integrative Health (NCCIH) notes that some studies suggest probiotics may lower the risk of antibiotic-associated diarrhea, but it is still unclear which strains, doses and timing help. NCCIH also cautions that people who are seriously ill or have weakened immune systems should be careful, and recommends checking with a health care provider first. That matters for exactly the kind of patients in this study.
5. If you’re in treatment for cancer, ask your care team
Transplant and oncology patients often have specific nutrition needs, like keeping weight up during chemo. Don’t change your diet on your own. Ask your oncologist or hospital dietitian whether reducing sweets during antibiotic courses makes sense for you.
The Bigger Picture on Diet and the Gut
This study adds to a growing pile of research showing the gut isn’t a closed system. What we feed it shapes what lives there. We’ve covered other surprising gut links too, like research showing ADHD is tied to more gut problems, and the steady stream of new findings on how we eat, sleep and move.
What makes the Nature study stand out is precision. Most nutrition research relies on people remembering what they ate. Here, every bite was recorded and stool samples were collected often, which the researchers say makes it among the largest and highest-resolution studies of its kind.
Marcel van den Brink, MD, PhD, chief physician executive at City of Hope and a co-senior author, said studies like this help explain how everyday factors, including diet, may affect the delicate balance that influences how patients respond to treatment and recover.
The Bottom Line
The link between sugar and antibiotics is a promising lead, not a settled rule. In very sick hospital patients, more sugar during antibiotic treatment tracked with a bigger hit to gut diversity and more of a risky bacterium, and mouse experiments backed that up.
Your takeaway for the next time you’re handed a prescription:
- Finish the full course exactly as directed.
- Skip the extra sodas, candy and desserts while you’re on it.
- Fill your plate with fiber-rich whole foods.
- Ask before starting probiotics, especially if you have a serious health condition.
This article is for general information and isn’t medical advice. Talk to your doctor or pharmacist before changing your diet or medications. Stay tuned to USA One News for more on the latest health research.
