The very low carbohydrate, high fat ketogenic diet has been linked to improved memory and longevity in mice, although it did lead to weight gain.
The findings of two independent mouse studies, published in journal Cell Metabolism, have raised the hope that ketogenic diets can extend the length of time someone lives in good health.
"The older mice on the ketogenic diet had a better memory than the younger mice. That's really remarkable," said senior author of the paper Eric Verdin, President and CEO of the Buck Institute for Research on Ageing in California.
"The fact that we had such an effect on memory and preservation of brain function is really exciting," he said.
However, mice allowed to remain on the ketogenic diet will eventually become obese, he said.
The 'keto' diet is where carbohydrate intake is so low that the body shifts to producing ketones to help fuel organs. Both fasting and exercise can also kick off the process of ketosis. The keto diet is so ultra low in carbs it also causes ketosis, whereas other diets can be low in carbs but not produce this.
US researchers fed the mice in both studies one of three diets starting in mid-life: a ketogenic diet, a control diet, or an average low-carb, high-fat diet.
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For the ketogenic diet, 90 per cent of the calories came from fat.
The researchers then tested the mice at various ages in tasks such as mazes, balance beams, and running wheels.
Further testing, revealed that the diets influenced insulin signalling and gene expression patterns typically found in fasting.
While both studies showed improvements in mid-life lifespan and memory tests, one study also found that a ketogenic diet preserved physical fitness, such as grip strength, in old age.
"The magnitude of the changes surprised me," said senior author Jon Ramsey, PhD, a professor at the University of California Davis.
Professor Helen Truby from the Department of Nutrition, Dietetics and Food at Monash University says to ensure the body remains in a state of 'ketosis' means consuming extremely low levels of carbohydrate, which can be difficult for many people.
Prof Truby warns it could also mean people miss out on important nutrients.
"This would mean in a human adult only 20-30g of carbohydrates per day - a dietary pattern that would lead to deficiency in vitamins and minerals unless the diet is carefully constructed, and would usually require micro-nutrients and minerals to be provided by supplements," Prof Truby said.
