Food fats are a combination of saturated,
monounsaturated and polyunsaturated fatty acids. Nutritionists often classify
fats according to the type of fatty acid present in the greatest amount.
Thus, some fats like beef tallow, butter, coconut, and palmkernel oils
are known as saturated fats. Products such as corn, soybean, sunflower,
and safflower oils are called polyunsaturated fats. Canola, olive and peanut
oils are known for their monounsaturated fatty acid content. In general,
saturated fats are solid at room temperature. They are more stable than
unsaturated fats and have less chance of breaking down or becoming rancid
over time. That is why saturated fats are often the candidate of choice
for commercial frying.
Unsaturated fats, both polyunsaturated and
monounsaturated, are liquid at room temperature. We typically think of
vegetable oils as good sources of polyunsaturated and monounsaturated fats,
and low in saturated fats. The exceptions are coconut and palm kernel oils.
They contain more than 80 percent saturated fatty acids by weight. Nutritionists
recommend that both polyunsaturated and monounsaturated fats be kept at
approximately 10 percent of calories. Vegetable shortenings are a blend
of many types of vegetable oils. The oil becomes solid or firm through
the process of hydrogenation. The result is a product that has a lower
polyunsaturated fatty acid content and a higher saturated fatty acid content
than liquid vegetable oils. Hydrogenation also forms monounsaturated fats
that have a different physical arrangement. These trans monounsaturated
fatty acids are similar in stability to saturated fatty acids. Research
shows their effect on blood cholesterol levels is variable. From ten percent
to almost one-third of margarines and hydrogenated vegetable shortenings
are trans fatty acids. Vegetable shortenings are less desirable than vegetable
oils as a food fat because of their fatty acid makeup. Similarly, margarines
are also blends of liquid vegetable oils and partially hydrogenated vegetable
oils. To keep saturated fatty acid content to a minimum use margarine that
lists liquid vegetable oil first in its ingredient label. In general softer
margarines are a better choice than those which are harder. |
