A ketogenic diet -- consisting of foods with very low levels of carbs -- is effective at controlling polycystic kidney disease (PKD), according to the first randomised controlled clinical trial.

PKD is an inherited disorder in which clusters of cysts develop primarily within the kidneys, causing the organs to enlarge and lose function over time.

The trial, published in the journal Cell Reports Medicine, aimed to investigate the effect of the fasting response known as ketosis on the cysts that are the hallmark of the disease.

"I'm really happy about these clinical trial results," said biologist Thomas Weimbs, at the University of California-Santa Barbara.

"We now have the first evidence in humans that the cysts really don’t like to be in ketosis and that they don’t seem to grow," he added.

For PKD patients, these findings represent an opportunity to control a genetic disease that leads to a progressive condition, causing pain and robbing them of their quality of life, and often resulting in the need for dialysis and kidney transplantation as the cysts destroy the kidneys’ ability to effectively filter and remove waste from the body.

"If you have PKD, the dogma is that it’s a genetic disease," Weimbs said. "And no matter what you do, you progress toward kidney failure and diet doesn’t make any difference, which unfortunately most patients are told to this day."

This prevailing belief was what the Weimbs Lab and colleagues from various research institutions in Germany set out to challenge with their trial. Sixty-six PKD patients were randomly split into three groups: a control group that received routine PKD counselling, another group that underwent a three-day water fast every month, and a third group that observed a low-carbohydrate, high-fat ketogenic diet.

The patients were followed closely with blood draws and MRI scans.

At the end of the three-month trial period, the researchers found that while the control group experienced the expected growth in the size of their kidneys, the ketogenic diet patients’ kidneys stopped growing and appeared to show a tendency to shrink somewhat, though the researchers pointed out that the shrinkage over the 90-day trial period failed to meet statistical significance.

The most striking evidence came in the form of measurably improved kidney function in the ketogenic diet patients, which was statistically significant. However, there is no one ketogenic diet to fit all, Weimbs said.

To get the best out of their diet, PKD patients should consult with their physicians and nutritionists as they shift away from the usual carbohydrate and sugar-laden standard diets that are pervasive in industrialised societies.