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A new Nature study suggests that eating more sugary foods during broad-spectrum antibiotic treatment may intensify disruption of the gut microbiome. In hospitalised stem-cell-transplant patients, higher sugar intake during antibiotic exposure was associated with a larger drop in microbial diversity and more Enterococcus. Mouse experiments supported a possible biological interaction. But the human study was observational and involved exceptionally ill patients, so it does not prove that everyone taking a routine antibiotic needs a sugar-free diet. The takeaway is modest: take antibiotics exactly as prescribed, and consider limiting sweets and sugary drinks without changing your treatment or any prescribed nutrition.
The study was published on 30 September 2026. It gives researchers an important new lead, but it does not establish a special “antibiotic diet”, a safe sugar threshold or a proven way to rebuild gut bacteria. Here is what the team did, what it found and what an ordinary reader can reasonably take from it.
The gut microbiome is the community of bacteria and other microorganisms living mainly in the large intestine. Researchers often measure its alpha diversity: how many different kinds of bacteria are present and how evenly they are represented. Diversity is not a universal score of “good” gut health, but a severe loss of it can signal disruption, particularly in medically vulnerable patients.
Broad-spectrum antibiotics act against many types of bacteria. That can be necessary and life-saving, but these medicines may also reduce gut bacteria that were not causing the infection.
The researchers studied 173 adults with blood cancers who were hospitalised for an allogeneic haematopoietic-cell transplant at Memorial Sloan Kettering Cancer Center between 2017 and 2022. The patients marked how much of each hospital meal they ate, while the team collected stool samples to track changes in their gut bacteria.
In total, the researchers recorded 9,419 meals containing 40,702 food items. They analysed 1,009 stool samples from 158 of the patients. All 173 received at least one antibiotic, and 138 were switched to broader-spectrum antibiotics after developing fever or other signs of a possible infection.
This gave the team unusually detailed food records. It was still not perfect: food brought in from outside the hospital was not always recorded, and illness, appetite, treatment and diet could all influence one another.
Sweets on their own were not clearly associated with lower microbiome diversity. The relationship appeared when patients had also received broad-spectrum antibiotics in the two days before a stool sample was collected.
During those periods, greater intake of foods classed as sugars, sweets and beverages was associated with lower bacterial diversity. It was also associated with greater expansion of Enterococcus faecium, a species that can take over after the wider microbial community has been disturbed and can cause serious infections in medically vulnerable people.
You may see reports saying that every additional 100 g of sweets was linked to a 24 per cent fall in microbial diversity. That needs context.
The researchers removed water from foods mathematically so that very different items could be compared on a common “dehydrated weight” basis. In their model, each additional 100 g of foods in the sweets category during broad-spectrum antibiotic exposure was associated with an extra 24.1 per cent reduction in average alpha diversity. A separate analysis based on grams of sugar produced an estimate of 20.6 per cent.
These are group-level statistical estimates, not an everyday serving guide. They do not mean that eating 100 g of mithai will cause exactly 24 per cent “damage”, and the study did not identify a safe or unsafe cut-off.
More detailed analyses suggested that added sugars contributed more strongly than naturally occurring sugars. Formulated sweet drinks, including sports drinks and oral nutritional supplements, were among the items associated with the pattern.
That last detail requires care. Some patients needed nutritional products because cancer treatment had left them unable to eat enough. A medically prescribed drink should never be stopped on the strength of this study; the clinical team must weigh microbiome questions against the immediate need for adequate nutrition.
Among patients with above-median, calorie-adjusted sugar intake, each additional day of broad-spectrum antibiotic exposure was associated with a 12 per cent higher estimated mortality hazard. The association was not statistically significant in the below-median group, and the two sugar-intake groups did not have significantly different mortality when antibiotic exposure was left out of the comparison.
This was an observational analysis, not evidence that sugar caused deaths or that reducing sugar would improve survival. The paper notes that patients with relatively sugar-rich diets also tended to eat less overall. Illness severity, poor appetite, treatment intensity and other factors may all have contributed.
The patient data could reveal a relationship, but not prove cause and effect. The team therefore gave mice one dose of a broad-spectrum antibiotic and compared animals receiving sucrose with those receiving a control supplement.
Among antibiotic-treated mice, sucrose increased the expansion of enterococci about 16-fold by day 3 and 33-fold by day 6. Sucrose without the antibiotic did not produce the same effect. Glucose, fructose and a commercial fruit smoothie also prolonged the bloom in related experiments.
A simple way to picture the result is to imagine the gut microbiome as a crowded neighbourhood. The antibiotic cleared out part of the community; in the mouse model, sugar then seemed to help Enterococcus occupy more of the open space. The researchers do not yet know exactly how. Sugar might support the expanding bacteria directly, weaken competitors or affect the host in a way that changes the gut environment.
No. This study does not establish a clinical rule that every person taking an antibiotic must eliminate sugar. The human participants were undergoing intensive cancer treatment and receiving hospital antibiotics, often broad-spectrum ones. That is very different from taking a short, routine course at home.
For many people, making sweets and sweetened drinks less frequent during treatment is a reasonable, modest choice. It is consistent with general healthy-eating guidance, but it is not a proven treatment for antibiotic-related microbiome disruption.
The study also does not justify banning fruit. The clearest human signal came from added sugars, while a commercial fruit smoothie had an effect in mice. Neither finding tells us what an ordinary serving of whole fruit does in a person taking antibiotics.
Nor did the study test fibre as a remedy. If you can eat normally, familiar meals containing dal, vegetables, fruit and whole grains can remain part of a varied diet, but they should not be presented as an antidote to antibiotics or sugar.
Separate from this antibiotic study, the World Health Organization advises keeping free sugars below 10 per cent of daily energy intake, with possible additional benefits below 5 per cent. Free sugars include sugars added to food and drinks, as well as those naturally present in honey, syrups, fruit juice and fruit-juice concentrates. This is general public-health guidance, not proof of an antibiotic-specific benefit.
The new study found that higher sugar intake during broad-spectrum antibiotic exposure was associated with a greater loss of gut-bacterial diversity and more Enterococcus in hospitalised transplant patients. Experiments in mice strengthened the case that sugar and antibiotics can interact under some conditions.
For the average person, the finding is a reason for proportion, not panic. Take the medicine you need exactly as prescribed. If your nutritional needs allow it, cutting back on sweets and sugary drinks during treatment is a cautious choice, but it is not a proven microbiome treatment and there is no evidence-based countdown for how long to continue afterwards.
For the broader everyday picture, read what a sweet-heavy day can feel like in your gut.
Disclaimer: This article provides general information and does not replace individual medical advice. Take antibiotics and prescribed nutritional products exactly as directed. Speak to a doctor or pharmacist if you have questions about your treatment or develop persistent, severe or worrying side effects.
The study does not prove that everyone needs to avoid sugar completely. It suggests that a sugar-rich diet may intensify microbiome disruption during broad-spectrum antibiotic exposure. Limiting sweets and sugary drinks may be a reasonable precaution for many people, but do not compromise prescribed nutrition or change your medicine.
This study does not show that whole fruit is harmful during antibiotics. The strongest human association involved added sugars; a commercial fruit smoothie produced an effect in mice. Those results do not justify removing ordinary whole fruit from your diet unless your clinician has given you a separate reason to do so.
The study did not test whether sugar makes an antibiotic less effective against the infection it was prescribed to treat. It examined changes in gut bacteria. Keep taking the medicine exactly as directed.
There is no proven universal “antibiotic diet”. Eat regular, varied meals that you tolerate, and follow any instructions given with your medicine. If you have been prescribed a nutritional supplement or a special diet, continue it unless your clinical team advises otherwise.
The study does not provide an answer. It did not test a fixed recovery period in ordinary antibiotic users, so recommendations such as three, seven or fourteen days would be invented rather than evidence-based.
No. It found an association between longer broad-spectrum antibiotic exposure and a higher mortality hazard in a subgroup of transplant patients with above-median sugar intake. It did not show that sugar caused deaths or that cutting sugar would improve survival.
