Media reports indicate that French medical orders have filed complaints against celebrity diet guru Pierre Dukan.
The Dukan diet was reportedly used by the Middleton family ahead of Kate's wedding to Britain's Prince William.
Both the French and the Parisian Medical Councils accuse Dukan, who promotes a high-protein diet that has seen him sell millions of books and win over a slew of famous followers, of breaking professional rules.
The man behind the "Dukan Diet Cookbook", which he is currently promoting in the United States, is accused of failing to observe two articles in the doctor's code: lacking prudence in statements potentially damaging public health, and of practising medicine as a business.
Dukan recommended in January that students in their final two years of high school be awarded extra marks if they manage to maintain an acceptable Body Mass Index (BMI), a measure of body fat based on height and weight.
He is accused of failing to take into account how his recommendation might affect anorexic or overweight students.
Dukan's publicist claims that he has sold 4.5 million books in France and around five million in the rest of the world, although the exact amount of money made is not public.
Dukan's lawyer insisted that his client has behaved no differently from other doctors with a public profile, and argued that he had raised a genuine public health issue.
"The fact that people are not indifferent to this book proves that it raises a major public health problem," said Isabelle Lucas-Baloup.
"Is a doctor advertising himself because he answers an interview request?" she said, noting that Dukan's being summoned did not amount to a condemnation.
At the time, Dukan denied that his high school suggestion would punish overweight children, saying: "There is nothing wrong with educating children about nutrition.
"This will not change anything for those who do not need to lose weight. For the others, it will motivate them."
France's health and nutrition watchdog ANSES has warned that certain diets can damage the kidneys because of an excess of proteins.
In July, Dukan lost a defamation suit against diet guru rival Jean-Michel Cohen who criticised his system.
In 2010, Dukan had three books in France's top 10 book sales of the year.