Two new studies, both conducted in mice, support each other's findings: that the ketogenic, or "keto," diet may improve memory in old age as well as prolong lifespan.
And two new independently conducted studies now suggest that the keto diet might help to improve memory and reduce mortality. One study - led by Drs. Eric Verdin and John Newman, both from the Buck Institute for Research on Aging in Novato, CA - looked at the effect of the keto diet on aging mice.
The second study - led by Dr. Jon Ramsey, from the University of California, Davis School of Veterinary Medicine - looked at adult mice and had similar findings about the impact of the keto diet, with the addition that it may also improve strength and coordination.
Both papers were published today in the journal Cell Metabolism.
Cyclical keto diet has health benefits
Both studies tested the effects of four diet types - ketogenic, low carbohydrate, high fat, or control - in mice. The scientists used tasks involving mazes, balance beams, and running wheels to test the development of the mice's cognitive skills and physical strength as they aged.
The researchers also monitored the mice for alterations in heart function, and any changes in the regulation of gene expression.
What the researchers at the Buck Institute - in collaboration with teams from other institutions - found was that the effects of the ketogenic diet on the body were very similar to those of fasting and other such dietary restrictions. For example, it impacted insulin signaling and gene expression in much the same way that fasting would.
The Buck Institute team found that a keto diet fed to mice on a cyclical basis - that is, alternated with the control diet - prevented obesity, reduced mid-life mortality, and prevented memory loss.
"The older mice on the ketogenic diet had a better memory than the younger mice. That's really remarkable," says Dr. Verdin.
The keto diet can raise the concentration of beta-hydroxybutyrate acid (BHB) in the body, which, the researchers note, improves memory function.
Dr. Verdin says that this is the first time that a study has detailed the beneficial impact of BHB on memory and lifespan in the case of aging mammals. "This opens up a new field in aging research. We think the health benefits of BHB may go beyond memory and could affect tissues and organ systems," he suggests.
Mechanisms call for further investigation
However, when the mice were tested for the impact of the keto diet on memory, they were off the diet and BHB levels had reverted to normal. This, the researchers explain, was in order to test whether or not the impact of a keto diet was long-term.
"We were careful to have all of the mice eating a normal diet during the actual memory testing which suggests the effects of the ketogenic diet were lasting. Something changed in the brains of these mice to make them more resilient to the effects of age. Determining what this is, is the next step in the work," says Dr. Newman.
One explanation for the durability of the effect on memory, he thinks, may be a change in gene expression. "Looking at gene expression," explains Dr. Newman, "the ketogenic diet suppressed the longevity-related TOR [target of rapamycin] pathway and insulin signaling and upregulated the fasting-related transcription factor PPAR-alpha, a master regulator that helps the body more efficiently metabolize fat."
The second study reports similar findings regarding the effect of the keto diet on memory and mortality, as its lead researcher explains.
"We expected some differences [in mice fed the keto diet], but I was impressed by the magnitude we observed - a 13 percent increase in median life span for the mice on a high-fat versus high-carb diet. In humans, that would be 7 to 10 years. But equally important, those mice retained quality of health in later life."
Dr. Jon Ramsey
The authors of this study also note that a keto diet allowed the mice to preserve their motor function and muscle mass.
Researchers involved in both studies are excited that their findings were mutually confirmed to a large extent. In terms of clinical implications, Dr. Verdin and his colleagues hope that further research may unlock the door to novel treatments for age-related cognitive disorders.
His laboratory at the Buck Institute is currently investigating how keto diets might impact Alzheimer's disease.