Are carbs the new fat? For much of the second half of the 20th century, doctors constantly suggested we avoid high-fat foods, but more recently a new target for our dietary scorn has emerged: carbohydrates. Two new companion studies are suggesting a ketogenic diet – high fat, low protein, and low carbohydrates – could enhance memory, improve physical strength and extend lifespan.

Whether you want to call it the Atkin's Diet, Paleo or simply "Keto," there have been plenty of variations on this way of eating. While some diets suggest no carbohydrates or sugars, many are underwritten by the same theory. The idea is that by severely restricting the body's intake of carbohydrates, a state known as ketosis is entered into. This forces the body to burn stored fats as fuel instead of carbohydrates.

A ketogenic diet certainly does result in weight loss, at least in the short term, but the long-term health effects of this kind of eating have long been cause for controversy among scientists.

A recent large-scale observational study published in The Lancet concluded that a high-carb diet was more dangerous to a person's health than a high-fat diet. The results made headlines around the world, but not all scientists were convinced. Criticisms of the study included a lack of clarity in regards to what types of carbohydrates were being recorded (processed sugars versus whole grains, for example) and a noting of the extreme levels of carbohydrate intake that the study used to constitute a "high-carb diet."

These two new companion studies have examined the long-term effects of a ketogenic diet on mice. The results are certainly fascinating, albeit nothing close to definitive.

Over at the University of California, Davis, the mice were split up into three groups: a high-carb diet, a low-carb/high-fat diet, and a ketogenic diet. The researchers made sure the calorie count of each diet was exactly the same in order to focus just on the metabolic effects.

"We expected some differences, 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," says senior author Jon Ramsey. "In humans, that would be seven to 10 years. But equally important, those mice retained quality of health in later life."

The mice on the ketogenic diet also displayed increased motor function and a reduced incidence of tumors.

The second study, conducted by the Buck Institute for Research on Aging in California, was constructed with a similar three-group design. This study found no extension to overall lifespan in the ketogenic-fed mice, but they did display a lower risk of dying between the ages of one and two years old.

The most interesting effects seen in the Buck study came in the cognitive tests. The mice fed a ketogenic diet displayed no age-related decline on memory tests, performing just as well in old age as they did in middle age. The ketogenic mice also displayed more exploratory behavior than the other diet groups.

"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," says lead scientist on the study, John Newman. "Something changed in the brains of these mice to make them more resilient to the effects of age."

While the team at the Buck Institute is cautious to note that these results shouldn't necessarily be mirrored in humans, the UC Davis researchers more explicitly suggest their results can be.

"In this case, many of the things we're looking at aren't much different from humans," says Ramsay of the UC, Davis research. "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 aging."

Undoubtedly, this recent wave of pro-low-carb and ketogenic diet research will spur a new interest in the dietary phenomenon, but the long-term health effects in humans are still not clear.

A healthy human diet involves more than simple generalizations. Does this high-fat/low-carb plan address salt intake? Is anyone removing carbs from their diet still getting the necessary nutrients they would otherwise get from more complex carbohydrates like whole grains?

Eric Verdin, President of the Buck Institute, suggests the best outcomes from this research are the new therapies that can be developed. Understanding how ketones interact with our cognitive faculties for example, will help target new opportunities for anti-aging therapies. The Buck Institute is also currently looking at how a ketogenic diet affects mice with Alzheimer's disease.

In the meantime, Verdin suggests we think about exercising more if we are excited by this ketogenic research. "Exercise also creates ketone bodies – that may be one of the mechanisms why it shows such protective effects on brain function and on healthspan and lifespan," he says.

The Buck Institute study was published in the journal Cell Metabolism, while the UC, Davis study was published in the journal Cell Metabolism.

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