Daizy we use the word diet in two different ways in English. It can refer to the type of food you eat (a vegetarian diet, a high-fat diet, a pasta diet etc) and we also use it to refer to when you try to lose weight (I’m on a diet so I’ve stopped eating chocolate) I wasn’t sure whether you meant a vegetable diet (where you eat lots of vegetables) or a vegetarian one (where you don’t eat any meat or fish)