More Than a Week of Keto Might Not Be Good for You

Trendy high-fat, high-protein diet may offer greatest health benefits if practiced only short term
February 10, 2020 Updated: February 10, 2020
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A ketogenic diet—which provides 99 percent of calories from fat and protein and only 1 percent from carbohydrates—produces health benefits in the short term, but negative effects after about a week, research in mice shows.

The results offer early indications that the keto diet could, over limited time periods, improve human health by lowering diabetes risk and inflammation. They also represent an important first step toward possible clinical trials in humans.

The keto diet has become increasingly popular as celebrities, including Gwyneth Paltrow, Lebron James, and Kim Kardashian, have touted it as a weight-loss regimen—at least for periods of time.

In the study, researchers found that the positive and negative effects of the diet both relate to immune cells called gamma delta T-cells, tissue-protective cells that lower diabetes risk and inflammation.

A keto diet tricks the body into burning fat, said lead author Vishwa Deep Dixit, professor of comparative medicine and of immunobiology at the Yale University School of Medicine. When the body’s glucose level goes down due to the diet’s low carbohydrate content, the body acts as if it is in a starvation state—although it is not—and begins burning fats instead of carbohydrates. This process in turn yields chemicals called ketone bodies as an alternative source of fuel. When the body burns ketone bodies, tissue-protective gamma delta T-cells expand throughout the body.

This reduces diabetes risk and inflammation, and improves the body’s metabolism, said Dixit. After a week on the keto diet, he said, mice show a reduction in blood sugar levels and inflammation.

But when the body is in this “starving-not-starving” mode, fat storage is also happening simultaneously with fat breakdown, the researchers found. When mice continue to eat the high-fat, low-carb diet beyond one week, Dixit said, they consume more fat than they can burn, and develop diabetes and obesity.

“They lose the protective gamma delta T-cells in the fat,” he said.

Long-term clinical studies in humans are still necessary to validate the anecdotal claims of keto’s health benefits.

“Before such a diet can be prescribed, a large clinical trial in controlled conditions is necessary to understand the mechanism behind metabolic and immunological benefits or any potential harm to individuals who are overweight and prediabetic,” Dixit said.

There are good reasons to pursue further study: According to the Centers for Disease Control, approximately 84 million American adults—or more than one out of three—have prediabetes (increased blood sugar levels), putting them at higher risk of developing type 2 diabetes, heart disease, and stroke. More than 90 percent of people with this condition don’t know they have it.

“Obesity and type 2 diabetes are lifestyle diseases,” Dixit said. “Diet allows people a way to be in control.”

With the latest findings, researchers now better understand the mechanisms at work in bodies sustained on the keto diet, and why the diet may bring health benefits over limited time periods.

“Our findings highlight the interplay between metabolism and the immune system, and how it coordinates maintenance of healthy tissue function,” said Emily Goldberg, the postdoctoral fellow in comparative medicine who discovered that the keto diet expands gamma-delta T cells in mice.

Dixit said it will be good news if later studies discover the ideal length of the keto diet for health benefits is relatively short.

“Who wants to be on a diet forever?”

The research was funded in part by grants from the National Institutes of Health. The research appears in Nature Metabolism.

This article was originally published by Yale University. Republished via Futurity.org under Creative Commons License 4.0.