Nutrition: As a general rule, many 3-day diets do not provide the calories or nutrition that your body needs. Most limit caloric intake to 1,000 calories or less. Additionally, it would be impossible to stick to these diets and get your recommended intake of fruits, vegetables, and other nutritious foods. When consuming less than 1,200 calories per day, it is very difficult to obtain your vitamins and minerals from foods, alone. Following this diet will require supplementation and assistance from a health professional like a registered dietitian nutritionist.