Fatty foods have the same problem as greasy foods; they are a lot of trouble for the body to digest. Generally speaking, somebody who has just given blood should concentrate on simple carbohydrates found in fruits like bananas, cherries, grapes, mangoes, and oranges. Conversely, they should avoid anything with a lot of fat or protein, as it takes the body more time and energy to digest these foods. Blood donors should also avoid fatty foods before giving blood, as the fat will interfere with the tests for infectious diseases. This is true even of foods like avocados that contain healthy fats.