High-protein diets, such as the Dukan diet, are currently a popular alternative to the traditional calorie-counting forms of dieting. But scientists at the University of Granada in Spain have shown through tests in rats that a high-protein diet increases the risk of kidney stones and other renal diseases.

Dr. Pierre Dukan’s high-protein diet has received a boost in popularity in recent years, due to reports that the diet helped the Duchess of Cambridge get thin enough to fit into her wedding dress and allegedly restored the postpartum figure of Jennifer Lopez.

In Dukan’s native France, approximately 2 million people are believed to follow the diet.

But the diet has been controversial. The British Dietary Association ranked the diet at number 1 in their annual rundown of diets to avoid in 2010, 2011 and 2012.

They point out that even Dr. Dukan himself – who was banned from practicing as a GP in France in 2013 – has warned of health issues associated with the diet, including lack of energy, constipation, vitamin and mineral deficiencies and bad breath.

In 2012, Medical News Today reported on a study finding that four-fifths of Dukan followers had put all their lost weight back on within 36 months. This kind of of body weight fluctuation can put dieters at increased risk of hypertension, diabetes and heart disease.