Eating a milkshake while on antibiotics could wipe out even more of your gut bacteria than the drugs alone.
Quick Take
- A new study links high sugar intake during antibiotic treatment to a steeper drop in gut bacteria diversity.
- Every 100 grams of sugary food or drink during antibiotics was tied to a 24% bigger loss in microbiome diversity.
- The sugar-antibiotic combo also boosted levels of Enterococcus faecium, a bacteria that can cause dangerous hospital infections.
- Mouse experiments backed up the human findings, showing sugar can fuel bacterial overgrowth during antibiotic use.
What Researchers Found About Sugar and Antibiotics
Scientists tracked eating habits and gut bacteria in hospitalized patients taking antibiotics. People who ate more high-sugar foods during treatment ended up with a less diverse gut microbiome. For every 100-gram increase in sugary food or drink, roughly the amount in one large milkshake, bacterial diversity dropped an average of 24% more than it otherwise would have.
Gut diversity matters because a wide mix of bacteria keeps harmful microbes in check. When antibiotics wipe out competing species, opportunistic bugs can take over. This study suggests sugar speeds up that takeover, leaving patients with fewer helpful bacteria standing guard in their digestive system.
A Dangerous Bacteria Gets a Boost
The research zeroed in on one organism in particular: Enterococcus faecium. This bacteria can cause severe infections in hospital settings, especially in patients with weakened immune systems. The study found that sugar intake combined with antibiotic use led to increased numbers of this bacteria, raising concern for patients already vulnerable to infection.
A related analysis of bone marrow transplant patients found the effect was even sharper in that group. Researchers reported a 51.8-fold increase in Enterococcus by day three and a 42.4-fold increase by day six among patients who ate more sugar during antibiotic treatment. Follow-up testing showed that fructose and glucose alone, the simple building blocks of table sugar, were enough to trigger the same bacterial bloom.
From Hospital Beds to Mouse Cages
To confirm the pattern was not just a coincidence, researchers turned to mice. Animals given sugar alongside antibiotics showed the same kind of bacterial imbalance seen in human patients, with Enterococcus expanding while overall diversity shrank. The team described this as validation “in vivo,” meaning the effect held up in a living, controlled experiment rather than just in patient records.
That combination of human data and animal testing strengthens the case. The original paper describes the work as “observational evidence that consumption of dietary sugars, in the form of sweets food-group items, during or after antibiotic exposure decreases microbiome diversity and drives Enterococcus expansion”. In plain terms, sugar and antibiotics together seem to create ideal conditions for the wrong bacteria to thrive.
Why This Matters Beyond the Hospital
The clearest findings so far come from hospitalized patients, including people recovering from bone marrow transplants, whose microbiomes are already under heavy stress from illness and treatment. Researchers analyzed more than 9,400 meals eaten by 173 hospitalized patients and examined stool samples from 158 of them to build this picture.
That hospital setting is worth keeping in mind. It does not mean the biology stops mattering for everyday antibiotic users, but it does mean the sharpest numbers reflect a specific, high-risk population rather than someone finishing a routine course of amoxicillin at home.
A Simple Takeaway for Anyone on Antibiotics
The practical lesson here is straightforward and lines up with basic common sense: when your body is already fighting off illness and dealing with powerful medication, loading up on sugar is not doing your gut any favors. Cutting back on sweets and sugary drinks during antibiotic treatment appears to be a simple, low-cost way to protect the bacteria your body depends on.
Slashing sugar intake before antibiotics may save your microbiome https://t.co/Bmw3lqTAws pic.twitter.com/jXRgtdY5Hn
— New Scientist (@newscientist) September 30, 2026
None of this requires a prescription or a doctor’s visit to act on. It is the kind of commonsense dietary choice that patients can make on their own while taking antibiotics, and the research so far suggests it could make a real difference in how well the gut bounces back afterward.
Sources:
newscientist.com, kxan.com, businesswire.com, link.springer.com
