"going on a diet" means being moderate in eating and drinking.

　　as we know, our body is a balanced system which needs a reasonable diet. a reasonable or balanced diet can help people keep fit because it not only prevents them from eating too much fat which may cause many diseases but aisc provides them with sufficient nutrition to guarantee that their body operates properly. besides, going on a diet can aisc help people, especially young ladies keep a slender figure, which will of course beautify their life.however, every coin has two sides. going on a diet is no exception. if carried to extremes, going on a diet may even become dangerous to our health. as we know, eating too much will result in corpulence, while eating too little wili lead to malnutrition, which is also the cause of many diseases, obviously, going on a diet doesn't mean eating too little, such a misunderstanding must be avoided.

　　in my judgement, not everybody needs to go on a diet. good health should be our primary concern. if your purpose is to have a slender figure, a diet should be carried only to the extent that your health is not affected.