It's pointed out in the passage that fad diets……

The term dieting most often refers to the revision of food intake in order to lose weight. People often find diets hard to maintain, in part because they have unrealistic expectations about how quickly they can lose weight. They blame the diet itself and try another one. Many fad diets are unhealthy and even dangerous if followed for any length of time. Proper weight-loss diets observe good nutritional practices and balanced food intake, including the recommended daily intake of vitamins and minerals.