A trick dolphins use to keep their big brains fed with energy could potentially lead to a cure for adult diabetes, according to scientists in the United States.
Experts have discovered that bottlenose dolphins can turn a diabetic-like state on and off as needed to maintain their blood sugar levels.
They believe a now-dormant genetic mechanism of the same type may have once evolved in people - and for similar reasons.
In both dolphins and ancient humans it would ensure that during lean times enough energy-giving sugar was always on hand to meet the demands of a large power-hungry brain. Understanding how the switch works and learning how to control it could be the solution to Type-2 diabetes, a disease that accounts for 5% of all human deaths worldwide, the US researchers claim.
Dr Stephanie Venn-Watson, director of clinical research at the National Marine Mammal Association in San Diego, California, said: "If dolphins have a genetic fasting switch that can turn diabetes on and off, identifying and controlling such a switch in humans could lead to a cure for Type-2 diabetes. Maybe there is something dormant in us that can be awakened and used to provide therapy or a cure."
Dolphins have a high-protein, low-carbohydrate fish diet that can pose problems for a creature with a such large brain. Brain cells demand a lot of energy, which is obtained from sugary glucose. Humans get much of their glucose from carbohydrates, but the liver can also produce it from protein. When carbohydrates are absent from the diet, levels of blood sugar can easily fall.
In animals with smaller brains, this is not too critical an issue. But it matters a great deal to big-brained creatures such as humans and dolphins, say the researchers. Bottlenose dolphins get round the problem by making themselves insulin resistant when fasting between meals. The hormone insulin, which regulates the way glucose is taken up and stored, is then less able to lower blood sugar levels.
Insulin resistance in humans is the key cause of Type-2 diabetes, which results in blood sugar rising too high. This can inflict damage to body tissues that can lead to heart disease and organ failure. But the researchers believe millions of years ago insulin resistance may have benefited humans surviving in a harsh ice age environment when food was scarce.
"Our ancestors' primary diets were high in protein and low in carbohydrates," Dr Venn-Watson told the annual meeting of the American Association for the Advancement of Science in San Diego. "It has been hypothesised that insulin resistance was selected for because it was beneficial during the ice age."
But the trait may have turned into a potentially dangerous condition when energy-rich foods later became plentiful, she said. Scientists had already found evidence of a gene similar to the "switch" in dolphins that was abnormally active in diabetes patients. "Maybe that's the smoking gun," said Dr Venn-Watson.