I mean if i follow a diet to lose weight about 1200 calorie should i put oil in ny food or can i replace it by fruit?

Be aware: That a 1200 cal/day diet is a rather restricted caloric intake. It will help you lose weight but isn't a sustainable diet. It also may predispose you to micronutrient deficiency(think minerals and vitamins), so consider a supplement for this. Fruit are fine, but don't forget the veggies. Just be aware, oils can be great but they are calorically dense, so be mindful of how much use are using.