4. Passage 3 Dieting to lose weight has become very popular in recent years. People have become more health conscious and try to take better care of their bodies by eating more nutritiously and exercising more regularly to lose any unnecessary fat that they may have. Not only are people being more careful about what they eat， they are also concerned with how they eat and how their meals are prepared. People are taking more time for each meal. Many avoid the so called ―plastic‖ fast-food hamburgers and choose to eat a salad or a sandwich of more healthful ingredients(成分) in a quiet restaurant with a more leisurely atmosphere. At home， they also try to take enough time to eat a relaxing dinner without phone or TV interruptions. While dieting may be viewed as beneficial， it has also become a serious problem for Americans， particularly for young women. Dieting for them has actually become a psychological addiction( 依 赖 ). They eat so little that they can lose as much as fifty percent of their total body weight， and although they look like skeletons， they still insist that they are fat. The current waves of exercising， dieting and the problems produced have caused many organizations to begin educating the public. Many schools， hospitals， health organizations， newspapers and magazines， for example， are offering classes， printing booklet articles， etc. to inform the public of the way to exercise and diet， of the dangers of dieting too rapidly， and of the places people can go for medical help if they find themselves on the road to ―diet addiction‖. The main idea of the last paragraph is about( ).