of fat harmful
Fat is one of the most maligned nutrients, blamed for obesity and heart disease. However, like so many things in nutrition, fat alone is not to blame. Excess consumption of certain types of fat is the real concern.
Not always appreciated is the importance of having adequate amounts of fat in the diet. The recent Dietary Reference Intake (DRI) report from the Institute of Medicine stresses that there are adverse effects from both low-fat and high-fat diets.
Certain components of fat, called essential fatty acids, are actually essential nutrients for normal health. Other components may promote health, but only when consumed in reasonable amounts.
Question: Are fats absolutely necessary in the diet?
Answer: Yes. Some fat is needed to facilitate the normal absorption of the fat soluble vitamins A, D, E, and K. Also, essential fatty acids play critical roles in maintaining healthy skin, cardiovascular function and normal blood clotting.
Q: This seems to contradict recommendations to eat less fat. Aren't fats bad for you?
A: The recent DRI report recommends that 20 to 35 percent of the calories in a person's diet should come from fat. For a typical 2,000-calorie diet, this amounts to 45 to 75 grams, or about 3 to 5 tablespoons, of oils and fats combined. Depending on the amount of fats in the food you eat, much of this can be obtained through a variety of foods, along with added fats and oils.
Q: Which fats are essential?
A: Two components are known to be essential -- the fatty acid components called linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid). Other fatty acids found in fats are known to be beneficial, but are not required by the body.
Q: What foods are the best sources of these two essential fatty acids?
A: Some plant oils are very good sources. Canola, hemp seed, soybean, walnut and wheat germ oils contain a good balance of both omega-6 and omega-3 fatty acids. Flax seed oil is very high in the omega-3 fatty acid, but relatively low in omega-6. Corn, cottonseed, grape seed, macadamia nut, olive, peanut, safflower, sesame, almond and avocado oils are all low in the omega-3 fatty acid and some are also low in the omega-6 fatty acid.
Q: Isn't olive oil supposed to be the most healthy oil?
A: Olive oil is high in monounsaturated fatty acids and possibly antioxidant phytochemicals, but it is a poor source of essential fatty acids. Most cultures that use olive oil also include fish in their diets. Fish provide the more potent omega-3 fatty acids EPA and DHA. These reduce the need for alpha-linolenic acid, the omega-3 fatty acid in plants.
Q: How much of these oils is necessary for a healthy diet?
A: The following amounts of oils meet the recommended levels for daily intake of essential fatty acids for an adult man (amounts for adult women are about 30 percent less):
>> Soybean: 5 teaspoons (210 calories)
>> Canola: 4 teaspoons (180 calories)
>> Walnut: 3 teaspoons (140 calories)
Like many things, too much or too little of these oils can be bad for health. Balance, variety and moderation -- yet again!
Alan Titchenal, Ph.D., C.N.S., is a sports nutritionist in the
Department of Human Nutrition, Food and Animal Science,
University of Hawaii-Manoa.
Joannie Dobbs, Ph.D., C.N.S., is a food and nutrition consultant
and owner of Exploring New Concepts, a nutritional consulting firm.
She is also responsible for the nutritional analyses
indicated by an asterisk in this section.