The main idea behind the Dukan Diet - and earlier versions such as the Atkins diet - is that you cut out or reduce carbohydrate and fat based sources of energy and replace them with protein. The lack of fats and carbs forces the body into a state of ketosis (heightened levels of compounds called ketone bodies) which means that it has to burn its fat reserves to provide energy, as the usual energy sources aren't coming in.

This does work - if you use up your fat reserves, you will naturally lose weight. However, as you are not getting many of the minerals and vitamins you need, there are severe side effects including dizziness, nausea and bowel problems. Some people have also noticed bad breath due to the change in intake, and in the longer term skin and hair problems.

Pierre Dukan, the inventor of the diet, has recently been criticised by a panel of French health professionals.