While small amounts of trans fats are naturally present in meats and dairy products from cows, sheep, and other ruminants, the great majority of trans fats in our diet are industrially-produced, contained in foods made with partially hydrogenated vegetable oils. Partial hydrogenation, which converts vegetable oils into semi-solid fats for use in margarines, commercial cooking, and manufacturing processes, converts approximately 30% of the natural fats to trans fats.