The Anglo-Dutch company said it has instructed all of its brand directors and agencies to use a Body Mass Index (BMI) of between 18.5 and 25 as a guideline when selecting models for its advertising. The range is consistent with UN guidelines on healthy BMI levels.
Unilever said it was making the move as a response to "growing societal concerns about the possible negative health effects that could occur should people pursue unhealthy or excessive slimness".
The company has previously been praised for eschewing skinny models in favour of using larger "real-life" models in its long-running "Real Beauty" campaign for the Dove brand.
Ralph Kugler, president of home and personal care at Unilever, said: "Unilever has adopted a new global guideline that will require that all its future marketing communications should not use models or actors that are either excessively slim or promote 'unhealthy' slimness.
"Unilever believes in a healthy balanced diet and that both men and women have the right to feel comfortable with their bodies and not suffer from lack of self-esteem brought on by images of excessive slimness."
Separately, Unilever is beefing up its commitment to responsible advertising with plans to restrict its marketing activity to children aged between 6 and 11 to the healthier brands in its portfolio.
Its new policy will cover food and beverage products, which have a positive nutritional profile and qualify for its "Choices/Eat Smart - Drink Smart" programme.
The new rules will be fully implemented across the globe by the end of 2008. The move builds on a voluntary restriction imposed just over a year ago, preventing the company from directly targeting its marketing at children below six years of age.
Vindi Banga, president of foods at Unilever, said: "We see this as a further step in responding to growing concerns about rising levels of obesity and dietary deficiency, particularly among children.
"This supports Unilever's broader strategy to improve the overall nutritional composition of our foods and to help parents and their children make 'healthier choices' without compromising on taste and enjoyment."