By Alan Mozes
WEDNESDAY, May 20, 2020 (HealthDay News) – The now-fashionable keto diet is said to turn fat into fuel. But a new small study says it can also change the wide variety of microbes that reside in the gut (the microbiome).
That could be a good thing, since those changes can ultimately strengthen the immune system by reducing inflammation, the researchers say.
The keto diet, which severely restricts carbohydrates and emphasizes fat and protein, has been touted as a way to control epilepsy, diabetes, and waist expansion. However, despite its increasing popularity, it remains controversial and much is unknown about its true impact on health.
The new finding follows a two-month study that tracked diet-related changes in microbiome content among 17 overweight or obese men, with follow-up testing in mice.
"A lot of work has been done on keto diets," said study author Peter Turnbaugh, an associate professor of microbiology and immunology at the University of California, San Francisco.
"But we didn't know much about how these diets differ from other high-fat diets, how exactly they affect microbes, or whether these diet-induced changes to gut microbes are important," he said.
To find out, Turnbaugh and his colleagues first put half the men on a one-month "standard" Western diet made up of 50% carbohydrates, 15% protein, and 35% fat.
The other half started on a keto diet made up of 5% carbohydrates, 15% protein and 80% fat. After a month, the two groups changed.
Analysis of stool samples revealed that when participants switched to a keto diet, they experienced "significant changes" in the levels of 19 bacterial "families".
The researchers then extracted microbial samples from the guts of the keto group and inserted them into the guts of the mice. The result: a drop in levels of a critical cell that fights infection and is also known to promote inflammation in autoimmune diseases.
The mice were then exposed to low-fat, high-fat and low-carbohydrate ketogenic diet options, with a fat content that increased respectively from 12% to 75% to 90%. And those results were surprising on several levels, Turnbaugh said.
For one, the levels of gut microbes driven by a relatively high-fat diet were actually reduced by the low-carb keto diet, and vice versa.
This suggests that the microbiome responds differently as dietary fat increases to ketone-promoting levels when carbohydrates are restricted.
And while mice on the keto and high-fat diets gained more body weight than those on a low-fat diet, those on the ketogenic diet gained "significantly less" weight.
The other surprise, Turnbaugh said, was the role of the so-called "ketone bodies."
"Ketone bodies," he explained, "are chemicals produced in our bodies when our cells do not have access to dietary carbohydrates," such as when following a keto diet. That forces the body to use fat stores for energy, rather than carbohydrates. And scientists know that the by-product of that change is a steady increase in ketone production.
But Turnbaugh and colleagues found that a gradual increase in ketone levels in mice (caused by a keto diet) was accompanied by a gradual change in intestinal composition.
And that raised the question: Could increasing ketone levels alone, independent of diet, also alter intestinal composition? More mouse research, Turnbaugh said, suggested the answer is yes: "Ketone bodies can directly affect gut bacteria even in the absence of a complete diet."
Still, Turnbaugh cautioned that the current effort is "probably the tip of the iceberg" when it comes to better understanding the complex interplay between a keto diet, ketone bodies, the microbiome, and disease risk. The study was small and more research is needed.
Lona Sandon, who reviewed the findings, made a similar note of caution. She is an assistant professor of clinical nutrition at the Southwestern Medical Center at the University of Texas at Dallas.
"I am surprised that the keto diet showed potential effects on the gut microbiome that would lead to a reduction in inflammation in the mice," said Sandon. He added that previous research actually "suggests that high-fat / protein diets are detrimental to the microbiome and increase inflammation."
Sandon emphasized that a keto diet has disadvantages. On the one hand, although popular because "it can help control appetite," people should know that the "benefits initially seen decrease over time," he said. And, he cautioned, patients who were prescribed keto to treat other medical problems "often end up overweight and have higher cardiovascular risk factors."
The study was published in the May 20 issue of the journal Cell.
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SOURCES: Peter J. Turnbaugh, Ph.D., associate professor, Department of Microbiology and Immunology, University of California, San Francisco; Lona Sandon, Ph.D., MEd, R.D.N., L.D., program director and assistant professor, Department of Clinical Nutrition, School of Health Professions, University of Texas Southwestern Medical Center at Dallas; May 20, 2020, mobile
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