Keto diet linked to diabetes, fatty liver and high cholesterol, study finds

A new study in Science Advances examined the long-term health effects of a high-fat, very low-carbohydrate diet commonly promoted as the keto diet. The researchers tested whether ketosis-driven weight loss comes at a metabolic cost and tracked metabolic outcomes in mice over roughly one year.

In the experiment, researchers fed one group of male and female mice a high-keto diet consisting of about 90 percent fat. Three control groups received different diets: a low-fat diet with about 10 percent fat, a standard high-fat diet with around 60 percent fat, and a low-fat, moderate-protein diet with about 10 percent fat and 10 percent protein. Initially, the keto mice lost weight; however, as time progressed, they developed fatty liver disease, severe glucose intolerance and elevated blood lipids.

The team noted higher cholesterol in male mice compared with female mice across groups, and the keto group showed insulin sensitivity along with low insulin levels. Writing in the journal Science Advances, researchers stated that while weight gain was avoided relative to a traditional high-fat diet, the high-keto mice still developed adverse metabolic traits, including hepatic steatosis in males and impaired insulin dynamics.

Dr Molly Gallop, a postdoctoral fellow in metabolic biology at the University of Utah, commented on the findings: "We observed worsening glucose intolerance and impaired insulin secretion the longer the animals had been on a keto diet. Therefore, the keto diet as a treatment for metabolic disease should be questioned even if initial improvements in health are observed."

The study’s authors summarized the results by noting that the long-term use of a keto diet may have harmful effects on metabolic health and that further studies in other strains of mice, other animals and humans are necessary to determine whether keto-diet–linked metabolic derangements are universal. In the meantime, the researchers emphasized caution about viewing keto as a universal remedy for metabolic disease.

For perspective on how the diet is typically framed, the study notes that a classic keto pattern consists of about 75 percent fat, 20 percent protein and 5 percent carbohydrates. By contrast, the NHS’s healthy-balanced-diet guidance recommends roughly 30 percent fat, 15 percent protein and 55 percent carbohydrates. Those on keto commonly limit carbohydrates to about 20 to 50 grams per day; that can mean avoiding staples like bread, pasta, rice and many fruits. A slice of wholemeal bread carries about 14 grams of carbohydrates, and a medium banana around 20 grams, underscoring how carefully meals must be planned on such a diet.

Despite multiple studies that have pointed to potential risks, keto maintains popularity in popular culture. Celebrities such as Gwyneth Paltrow have spoken about following a low-carb approach in the past, while others including Jennifer Aniston, Halle Berry and Kourtney Kardashian have discussed the lifestyle. Aniston has since noted that she eats carbohydrates in moderation. Industry trends aside, experts caution that results observed in mice do not automatically translate to humans, and human studies are needed to determine long-term effects on metabolic health.

Overall, the new findings add to a growing body of questions about the safety of long-term ketogenic dieting and highlight the importance of individualized dietary choices guided by medical supervision, especially for people with preexisting metabolic concerns.