Eating a high-fat, low-protein and low-carbohydrate diet improves memory, brain function and physical ability in later life, a study in mice has found.

A lot of fat but very little protein or carbohydrate – known as a ketogenic or 'keto' diet – kicks the body into a state similar to fasting. The body begins to generate ketone bodies, which can fuel the body in the absence of carbohydrates.

A ketogenic diet has been linked to weight loss and some improvements in brain function in previous studies, but this is the first time it's been comprehensively associated with better brain function in older age.

Mice on the ketogenic diet were less likely to die between 1 and 2 years old. They performed no differently on memory tests in old age and middle age, while mice on the normal diet declined with age. The older ketogenic mice would also explore more. Even after they came of the ketogenic diet, their memory skills were still better than the mice on a normal diet months later.

"The fact that we had such an effect on memory and preservation of brain function is really exciting," said Eric Verdin, president and chief executive of the Buck Institute for Research on Aging and an author of one the papers on the mice.

"The older mice on the ketogenic diet had a better memory than the younger mice. That's really remarkable."

This equated to a 13% increase in median lifespan for the mice, according to the second paper on the mice in the same issue of the journal. So essentially, rather than living a much longer life, more of the mice were living to old age, with less cognitive decline.

"At a fundamental level, humans follow similar changes [to mice] and experience a decrease in overall function of organs during ageing," said Jon Ramsey of the University of California, Davis, an author of the second paper.

"This study indicates that a ketogenic diet can have a major impact on life and health span without major weight loss or restriction of intake. It also opens a new avenue for possible dietary interventions that have an impact on ageing."

However more research needs to be done before we can say humans would have the same health benefits as mice from following a ketogenic diet.

Duane Mellor, a human nutrition researcher at the Coventry University, welcomed the study but noted it would be a while yet before we know whether the ketogenic diet could be optimal for humans.

"You've got to admire the science they do," Mellor told IBTimes UK. "But how that maps onto the human diet is not yet known.

"We also would need to look at just how sustainable this would be to implement in human communities in terms of food supply."

A higher fat diet often means more animal products, which comes with a financial and ecological burden. For people wanting to improve their chances of living well to a ripe old age, Mellor recommends following the advice of agencies such as the World Health Organization.

"For good health and mental health, the recommendations are plenty of vegetables, fruit, eating a variety of minimally processed foods."