A ketogenic diet -- which provides 99 per cent of calories from fat and only one per cent from carbohydrates -- produces health benefits in the short term, but negative effects after about a week, say researchers.
The study, published in the journal Nature Metabolism, 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.
"Our findings highlight the interplay between metabolism and the immune system, and how it coordinates maintenance of healthy tissue function," said study researcher Emily Goldberg from Yale University in the US, who discovered that the keto diet expands gamma-delta T-cells in mice.
A keto diet tricks the body into burning fat, when the body's glucose level is reduced 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, the study said.
"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," said Indian-origin researcher and study lead author Vishwa Deep Dixit.
This reduces diabetes risk and inflammation, and improves the body's metabolism, said researchers.
After a week on the keto diet, 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, long-term clinical studies in humans are still necessary to validate the anecdotal claims of keto's health benefits," Dixit said.
"Obesity and type 2 diabetes are lifestyle diseases, diet allows people a way to be in control," he added.
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.
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