A ketogenic diet — which provides
99% of calories from fat and only 1% from carbohydrates — produces health
benefits in the short term, but negative effects after about a week, Yale
researchers found in a study of mice.
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.
In the Yale
study, published in the Jan. 20 issue of Nature Metabolism,
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 of the Yale School of Medicine.
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. 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, the Waldemar Von
Zedtwitz Professor of Comparative Medicine and of Immunobiology. 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 pre-diabetic,” 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% 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.
If the ideal length of the diet for
health benefits in humans is a subject for later studies, Dixit said,
discovering that keto is better in small doses is good news, he said: “Who
wants to be on a diet forever?”
Journal
article: https://www.nature.com/articles/s42255-019-0160-6
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