Fats help the body to use certain vitamins. Some vitamins are soluble in fat, they are called liposoluble A, D, E, K. While they are soluble in water, the hydrosoluble vitamins are: group B and C. If you put a little oil on the salad, it is best olive oil, the body uses antioxidants, lycopene and beta-carotene. Fats stimulate the secretion of bile, which facilitates digestion and resorption of vitamins soluble in them. While the opposite is the case with calcium, it is better used from dairy products with a lower percentage of fat than from fatty products.