A new law entered into force on Saturday which compels all models operating in France to provide a doctor's note certifying that their Body Mass Index (BMI) is not too low and that they are in overall good health.
Under a second law, to come into force in October, all pictures of models that have been altered or photoshopped will have to carry a disclaimer to that effect.
The health ministry said the two measures aimed "to avoid the promotion of unattainable ideas of beauty and to prevent youth anorexia" as well as to protect the health of models, who are especially at risk from being
The doctor's note will be valid for two years and will look particularly at a model's BMI, with a reading under 18.5 classed underweight and liable to suffer from health problems.
BMI is calculated based on a ratio of height to weight with the average range generally between 18.5 and 24.9.
Employers contravening these laws could be liable to up to six months in prison and a fine of up to 75,000 euros ($82,500).
Some 600,000 young people are thought to suffer from eating disorders in France, including 40,000 people suffering from anorexia.
Eating disorders are the second most common cause of death of 15-24 year-olds, after road accidents.
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The new laws follow similar measures taken in Spain in 2006, which banned models with a BMI under 18 from Madrid Fashion Week.
Israel has also banned agencies from employing models with a BMI under 18.5, as well as photo-shopping.
In Italy, there is no precise law but the top agencies do not employ models with a BMI under 18.5.