Most of us leave the doctor's clinic with a strip of antibiotics and one clear instruction: finish the full course. Very few of us are told to think about the sweets, biscuits and sugary chai we have alongside those tablets. A new study suggests maybe we should.
- A 2026 study published in Nature linked higher sugar intake around antibiotic treatment to greater damage to gut bacteria.
- In 173 hospitalised patients, every extra 100 grams of sugar eaten in the 48 hours before treatment was tied to a further 21% drop in gut bacterial variety.
- Sugar appeared to help a hard-to-treat bacterium, Enterococcus faecium, spread in the gut.
- The human findings show a link, not proof, and come from seriously ill hospital patients.
- Going easy on sweets during a course of antibiotics is a low-risk step, but never change your treatment without your doctor's advice.
So, should you cut back on sugar while taking antibiotics? Early evidence says it may help. Antibiotics already thin out the helpful bacteria in your gut, and a large study from NYU Langone Health, City of Hope and Memorial Sloan Kettering Cancer Center found that people who ate more sugar around their treatment lost even more of that bacterial variety. The research is still early, but eating fewer sweets and sugary drinks during and right after a course of antibiotics is a simple, sensible habit with little downside.
What did the new study find?
The study, published in Nature on 30 September 2026, followed 173 hospitalised patients with blood cancers. Many were receiving antibiotics and chemotherapy, often as part of stem cell transplants, and stayed in hospital for weeks. This allowed the researchers to do something rare: they recorded 9,419 meals and collected stool samples almost every day.
When they matched what patients ate with changes in their gut microbiome, a clear pattern appeared. For every additional 100 grams of sugar eaten in the 48 hours before antibiotic treatment, the variety of gut bacteria, known as alpha diversity, fell by an additional 21%. A varied gut community is generally seen as a sign of a healthier, more resilient gut.
The team also tested the idea in mice. Mice given the antibiotic biapenem along with dietary sugar saw gut Enterococcus levels rise more than 16-fold by day three and more than 33-fold by day six.
Why would sugar make antibiotics harder on your gut?
Antibiotics do not pick and choose very well. Along with the harmful bacteria they are meant to kill, they also wipe out many of the helpful microbes that keep the gut balanced. That leaves empty space and spare food.
The researchers believe the bacteria that survive antibiotics may use simple sugars to grow quickly and take over. In this study, sugary diets combined with antibiotics were linked to a rise in Enterococcus faecium, a species known for causing infections that can be difficult to treat. The scientists are honest that they do not yet know the exact mechanism. Sugar may feed Enterococcus directly, weaken its competitors, or work in some other way.
Does this apply to everyday antibiotic use?
This is the important caveat. The patients in this study were very ill, had weakened immune systems and received strong antibiotics over long periods. A healthy adult taking a five-day course for a throat infection is in a very different situation, and the results cannot simply be copied across.
The human data also comes from observation, not a controlled trial, so it shows that more sugar and more gut damage went together, not that one definitely caused the other. The researchers say clinical trials are the next step. Still, the direction of the evidence fits with what we already know: the gut is easily disturbed by antibiotics, and a diet heavy in added sugar does it no favours. The World Health Organization already advises keeping free sugars below 10% of daily energy, and ideally below 5%, for general health.
Simple ways to go easy on sugar during a course of antibiotics
You do not need a strict diet. A few small changes for the length of your course, and a week or two after, are enough to start with:
- Skip the mithai, biscuits and packaged desserts for now, especially in the first few days.
- Choose water, plain buttermilk or unsweetened nimbu pani over packaged juices, colas and sweetened drinks.
- Reduce the sugar in your tea and coffee, or switch to a smaller cup.
- Lean on simple home food such as dal, khichdi, vegetables, whole grains and millets, which give your gut fibre to work with as it recovers.
- If you take curd, keep it plain rather than sweetened, and check with your doctor about timing, since some antibiotics should not be taken alongside milk products.
If you need something to snack on between meals, a savoury option is a better fit than a sweet one right now. Our Baked Ragi Chips are made with finger millet and baked rather than fried, which makes them an easy swap for a packet of biscuits.
Most importantly, always finish your antibiotics exactly as prescribed. Food changes are there to support your treatment, not replace it.
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Frequently Asked Questions
1. Should I avoid sugar while taking antibiotics?
Early research suggests cutting back may help protect gut bacteria. A 2026 Nature study linked higher sugar intake around antibiotic treatment to a bigger loss of healthy gut microbes. It was observational and involved hospitalised cancer patients, so it is not proof. Reducing sweets is low-risk, but always follow your doctor's advice.
2. Why do antibiotics upset the gut?
Antibiotics kill harmful bacteria, but they also wipe out many helpful microbes living in the gut. This can reduce bacterial variety, cause loose stools or bloating, and leave room for tougher bacteria to grow. Most healthy people recover over a few weeks, but repeated courses and a poor diet may slow that recovery.
3. What should I eat during a course of antibiotics?
Simple home-cooked meals are a good base. Dal, khichdi, vegetables, whole grains, millets and plain unsweetened curd are gentle on the stomach and provide fibre. Limiting sweets, packaged juices and sugary drinks may also help. Ask your doctor about food timing, since some antibiotics should not be taken with milk products.
4. Is Enterococcus faecium dangerous?
Enterococcus faecium normally lives in the gut in small numbers without causing harm. Problems arise when it overgrows, especially in hospital patients with weak immunity. Some strains resist common antibiotics, which makes their infections hard to treat. A 2026 study linked eating more sugar during antibiotic treatment to this bacterium spreading in the gut.
