Obesity has become a serious health problem affecting millions of people around the world. Obese people have a higher risk to attain chronic diseases, a reduced quality of life, and higher risk of premature death. Persuasive technology and virtual communities can help address these problems by motivating patients to follow a healthier life style. This paper presents the Persuasive Health Network (pHealthNet), a pervasive virtual community designed to promote a healthy lifestyle in patients with chronic degenerative diseases that participated in a national program for the prevention of diseases, education and self-care. The development and deployment of the system supports the program's goal of persuading patients to change their eating habits and to increase their physical activity. The system was incorporated in the program of two self-support groups whose participants are monitored for a period of three months. The results of an in situ evaluation showed that participants increased their trust in themselves, adopted healthier eating and exercising habits and where more satisfied with the program that those who followed the traditional approach.