Almost everyone considers going on a diet sometime in his or her life. All, regardless of sex and age, have something in common- -losing weight and losing it fast. Though their common aim may seem basically good, they probably do not realize that misguided dieting can do more harm than good to their health. Going on too strict a diet can destroy the balance of chemicals in the human body. This happens because when the body is suddenly given much less food than usual, it feels as though it is being attacked and tries hard to protect itself by saving energy. It does this by slowing down metabolism, the process by which the food we eat is converted into energy. As energy is supplied to the body at a slower and slower rate, dieters gradually become so weak that they can do nothing. They soon lose interest in everything going on about them, and their resistance to illness becomes so low that they are easily attacked by one illness after another. Most of those who diet know that foods like rice, bread, potatoes, cakes, sweets, fruits and some vegetables contain carbohydrates (碳水化合物),and so can make one fat. What they do not realize, however, is that carbohydrates are our bodies' main source of energy, and that these foods also contain components essential for the composition of substances that are needed to keep the body healthy. As a result, they try to avoid eating these foods, and consequently, they become weaker and less healthy. They begin to have difficulty sleeping properly and start to suffer from radical mood changes. In more serious cases, they even begin to show signs of mental illness. It is strange enough that most strict diets recommend artificial sweeteners to take the place of sugar and other natural sweeteners. In fact, such artificial sweeteners actually increase one's appetite and lead to one 's eating even more than usual. Of course, the fact that misguided forms of dieting result in so many problems does not mean that no dieting is safe or all dieting is harmful to the health. Proper dieting cannot only help a person lose ugly excess fat, but can also help him or her to keep it off and to lead a more active, happier and healthier life. You might ask just what a proper diet is. Well, simply expressed, a proper healthy diet is one that is well-balanced, or, in other words, one that includes enough but not too many of the kinds of foods that provide the body with the nutrients that it needs to function properly. The most important of these nutrients are the macronutrients: proteins, carbohydrates and fats. The body needs fairly large amounts of proteins and carbohydrates for building material and energy. Meat, fish, eggs, milk, cream, and nuts all contain proteins and foods like rice, bread, potatoes, etc contain carbohydrates. The body needs fat to keep it from the cold and to provide a protective layer for the organs, but only in small quantities. Vitamins and minerals such as iron, calcium, are another group of essential nutrients, though the body does not need as great a quantity of these as it does the macronutrients: proteins, carbohydrates and fats. One way of getting enough nutrients while keeping one S weight down is to take substitutes for foods which contain too much fat. For example, instead of regular milk, one can take skimmed milk. which contains as many proteins and minerals as regular milk but has had the fat removed. In the same way, vegetable oil can be used for cooking instead of animal oil. Now choose the best way to complete the sentences.