The ketogenic diet has gained massive popularity for weight loss, diabetes control, and metabolic health. But new research suggests that staying on keto long-term may come with serious hidden risks — even if the scale looks good.
A new study from University of Utah Health, published in Science Advances, has found that while a ketogenic diet prevented weight gain in mice, it also triggered fatty liver disease and impaired blood sugar control, raising concerns about the diet’s long-term safety.
Researchers followed adult mice fed different diets over several months. One group consumed a ketogenic diet (high fat, very low carbohydrates), while others were given a typical Western diet, a low-fat high-carbohydrate diet, or a low-fat diet with equal protein content.
As expected, mice on the ketogenic diet gained less weight than those on the Western diet. But inside their bodies, a different story was unfolding.
Despite staying lean, keto-fed mice developed fat buildup in the liver, a condition known as non-alcoholic fatty liver disease (NAFLD), a major risk factor for diabetes, heart disease, and liver failure.
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One of the most striking findings was a strong sex difference. Male mice experienced more severe liver damage, inflammation, and metabolic dysfunction than females. Female mice appeared partially protected from the worst effects, though researchers say the reason is still unclear.
This finding could help explain why some people thrive on keto while others experience fatigue, hormone issues, or abnormal lab results.
“We’ve seen short-term studies and those just looking at weight, but not really any studies looking at what happens over the longer term or with other facets of metabolic health,” said Molly Gallop, PhD, now assistant professor of anatomy and physiology at Earlham College, who led the study as a postdoctoral fellow in nutrition and integrative physiology at U of U Health.
The study also revealed major changes in how the body handles glucose.
After months on the ketogenic diet, mice had abnormally low blood sugar and insulin levels. But when carbohydrates were reintroduced, their blood glucose spiked dramatically and stayed elevated for long periods, a sign of impaired metabolic flexibility.
Scientists believe prolonged high-fat intake may stress insulin-producing cells in the pancreas, making it harder for the body to respond when carbohydrates return.
There was some encouraging news: when mice were switched back to a balanced diet, certain metabolic problems improved. This suggests that not all keto-related damage is permanent, especially if the diet is stopped early.
However, researchers warn that the study shows weight loss alone is not a reliable marker of health, adding that a person can look lean while serious metabolic issues are developing internally.
