Could Extreme Sugar Restriction Actually Be Hurting Your Gut Microbiome?
If you're trying to be healthy or lose weight, cutting down on sugar is widely considered one of the best things to do (in addition to being mindful about dietary fat intake).
But a new study presented at the Endocrine Society's annual meeting (ENDO 2026) suggests that going completely sugar-free while on a low-fat diet may actually do more harm than good (well, at least in mice). And it appears to come down to how these restrictions effects the microbiome.
What the researchers found
Researchers at the Dasman Diabetes Institute fed two groups of mice either a sucrose-free, low-fat diet or a low-fat diet that included sugar for 16 weeks. Sucrose is best known as table sugar. It's a combination of glucose and fructose. The study was done in mice because the animals actually share over 95% of their genes with humans but are much easier to manipulate and observe.
Scientists tracked the mice's blood sugar, insulin function, gut bacteria, and signs of inflammation in the colon and liver. Both groups weighed the same throughout, so any differences in health outcomes came down to diet composition alone, not weight gain.
The mice that ate no sugar developed a range of gut and metabolic problems:
- Gut bacteria imbalance: The sugar-free diet significantly disrupted the gut microbiome. Beneficial bacteria that help maintain gut health declined, including strains that produce short-chain fatty acids, which keep the gut lining strong. Meanwhile, bacteria associated with inflammation and stress increased.
- Colon inflammation: The bacterial imbalance triggered colonic inflammation, which presents as irritation and immune activity in the large intestine. The gut lining showed signs of damage, including a loss of the mucus-producing cells that protect it, and an influx of immune cells trying to respond to the disruption.
- Blood sugar and insulin problems: Mice developed impaired blood sugar control and reduced insulin sensitivity. These are early markers of metabolic dysfunction.
- Fatty liver changes: Consistent with what researchers call the gut-liver axis, the sugar-free diet also triggered inflammation and fat accumulation in the liver.
What this means for your gut
Your gut microbial diversity depends partly on what you eat. Certain beneficial bacteria are responsible for fermenting carbs and produce short-chain fatty acids (compounds that help maintain the gut lining, regulate immune responses) and support metabolic health. When sucrose was removed from the diet entirely, those bacteria declined. The downstream effects rippled through the gut, the immune system, and the liver.
Now this research doesn't mean sugar is always good for you. But it does suggest that your gut bacteria may need a certain amount of carbs to function well, and that cutting them out entirely can backfire.
"Completely removing sucrose from a low-fat diet may unexpectedly disrupt gut health and promote inflammation and metabolic dysfunction, highlighting that balanced nutrition is more important than simply eliminating sugar," said lead researcher Rasheed Ahmad, Ph.D., principal scientist and head of the Immunology & Microbiology Department at the Dasman Diabetes Institute.
Ahmad added that the research "may influence future dietary recommendations by emphasizing the importance of maintaining a healthy gut microbiome rather than focusing only on sugar restriction."
The takeaway
This was an animal study, and while mice and humans have a lot of similar DNA, more research is needed to understand how sugar elimination affects the human gut specifically. That said, the results add to a growing body of evidence suggesting that extreme dietary restriction, even of something widely considered "not healthy", can have unintended consequences.
Rather than eliminating sugar entirely, the researchers suggest eating a healthy balance of carbs to support gut and immune health. In practice, that might look like focusing on the quality and source of carbs (including foods like whole, grains, legumes, and fruit) rather than trying to eliminate sugar completely.