Lab rats fed a keto diet for up to a year -- decades in human time -- showed signs of liver and heart disease and developed glucose intolerance, according to a recently published study.

It sounds counterintuitive: Eat more fat and lose more weight.

But it's the underpinning of a keto diet -- a controversial eating regimen designed to retrain the body to rely on something other than sugar for energy. The regimen is rich in meat, eggs, high-fat dairy and oils.

"I think a lot of people look at a ketogenic diet and think, 'I'll lose weight, I'll be healthier,' " said lead researcher Molly Gallop, an assistant professor of anatomy and physiology at Earlham College in Richmond, Ind.

The biology goes like this: On a keto diet, a person's liver converts fat into molecules called ketone bodies that the body can burn for energy. Despite a high fat intake - up to 90% of daily calories - it can lead to substantial weight loss.

And while it may seem OK on the surface, new research in mice suggests that staying on a keto regimen for a long time might be risky.

Lab rats fed a keto diet for up to a year -- decades in human time -- showed signs of liver and heart disease and developed glucose intolerance, a team led by Gallop recently reported in the journal Science Advances.

"It's a cautionary tale," said study co-author Amandine Chaix, an assistant professor of nutrition and integrative physiology at the University of Utah in Salt Lake City. "This is not a magical dietary approach."

For the study, researchers put mice on one of four diets for about eight months. Body weight was lowest in animals in low-fat eating regimen, but those on a keto diet weighed less than those on a Western-influenced regimen.

That supports the idea that ultra-high-fat, low-carb food intake could help keep weight down.

But overweight people looking to slim down may want to proceed with caution. Results of studies done in animals often yield different results when repeated in people.

Still, the new findings raise concerns.

Mice given the keto diet had a key marker of heart disease - excess fat in their blood. Male mice also developed fatty livers and lab tests provided evidence that the organs weren't functioning as they should, the study found.

The most telling finding, Gallop and Chaix said, involved blood sugar.

Normally, the hormone insulin is secreted by the pancreas. This tells tissues to draw sugar from the blood and store to make energy. But insulin-making cells in keto-fed mice struggled to release the hormone. It's not clear why. Quitting the diet solved that problem.

The findings dovetail with the experience of a neurologist at Johns Hopkins in Baltimore who offers a keto diet as a treatment option for patients with epilepsy.

For more than a century, the diet has been used to treat folks with epilepsy, said the neurologist, Dr. Tanya McDonald, who reviewed the findings.

"We don't recommend that the general public use ketogenic diets without medical supervision," she said in a news release, adding that if they do decide to load up on such keto fare as nut-based french fries and extra cheese, they should let their doctors know so they can watch for potential problems.

More information

Harvard Health has more about how a keto diet works.

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