Frying french fries in beef tallow, lard, or other animal fats adds saturated fat to the diet. Replacing animal fats with tropical vegetable oils, such as palm oil, simply substitutes one saturated fat for another. For many years partially hydrogenated vegetable oils were used as a means of avoiding cholesterol and reducing saturated fatty acid content, but in time the trans fat content of these oils was perceived as contributing to cardiovascular disease. Starting in 2008, many restaurant chains and manufacturers of pre-cooked frozen french fries for home reheating phased out trans fat containing vegetable oils.