Kate and Carole Middleton's dietician Peirre Dukan, is under fire for his remarks that suggested slimmer teenagers should get higher exam marks at school.

Dukan, the doctor behind the high-protein Dukan Diet, faces a disciplinary hearing and could be struck off as a doctor for giving dangerous advice to teens who could already be struggling obesity or anorexia.

In January, Dukan breached medical ethics by telling teens there should be an extra exam subject called ideal weight, which slimmer pupils should pass just because they are thinner, the Daily Mail reported.

The French College of Physicians said Dukan has breached article 13 of the medical ethics code, which says: A doctor must be aware of the repercussions his views can have on the public

Doctors outside of France have also criticized Dukan's comments. Everything about this is wrong, Dr. David Katz, director of the Yale University Prevention Research Center told ABC News. It's wrong because it invites eating disorders. It's wrong because weight has nothing to do with academic performance ... and the notion that weight is a behavior that should incentivize is just wrong. Weight is an outcome. We should incentivize things people can control.

Many celebrities follow the diet including: Kate Middleton, Jennifer Lopez, and Katherine Jenkins.  But many health groups have criticized it for its low vegetable and carbohydrate intake. The British Dietetic Association said it was one of the worst celebrity diets because it cut certain food groups, which is not advisable. 

The Dukan diet comes in four phases, which promotes weight loss of up to 7 pounds per week. In the first 'attack' stage,users only eat lean protein and zero-fat dairy products.  In the second phase, dieters add non-starch vegetables on alternate days. Then food and vegetables can added in the final two stages.

Dukan has defended his comments, which came under scrutiny this week. Here is nothing unhealthy about educating youngsters about nutrition. My idea would change nothing for those who have no need to get thinner. But for those who do, it would only motivate them to lose weight, he told the Daily Mail.

Another complaint from the French College of Physicians said Dukan has been more focused on making money than on medicine, the BBC reported. He has sold over 7 million copies of his dieting books.

People in public health and medicine should first and foremost be committed to doing good, Katz said in an interview with ABC News. As long as they're being honest and honorable and using the available scientific evidence, I think it's OK [to make money as well]. I think when money is the priority; you don't belong in public health or medicine in the first place. If you want to make money, work on Wall Street.

The hearing will take place in six months and if charged Dukan could be removed from the French medical registry.