Understanding Dietary Fats
Author: Winston Craig, MPH, PhD, RD.
Is An Oil Change Needed?
Adults should consume at least 15 percent (but not more than 30 percent) of their calories from fat. So says the latest report from the World Health Organization. Dietary fat is necessary for the absorption of the fat-soluble vitamins (A, D, E and K) and also the carotenoid pigments that are important for our health. Fat also supplies the essential fatty acids - linoleic and linolenic acid. These compounds are precursors for important substances that regulate muscle contraction, blood clotting, inflammatory reactions and other important body functions.
Not All Fats Are Created Equal
But what type of dietary fat is best to achieve optimal health? Are the oils that are rich in omega-3 fatty acids (such as canola and flax seed oil) healthier than the oils rich in omega-6 fat (such as sunflower seed or corn oil)? Is the use of oils rich in monounsaturated fat (such as olive oil) associated with better health than those oils rich in polyunsaturated fat (such as soy or safflower oil)? Do the partially hydrogenated oils (used in fast foods, bakery products, shortenings and some margarines) which contain trans fatty acids, cause any harm? Is margarine any better than butter? These are some of the questions that people are asking today as they search for an optimal diet.
The omega-3 fat gained a measure of popularity because of earlier studies which showed that Eskimos who ate a large quantity of seal and fish were protected against heart disease. Fish and marine mammals do contain substantial amounts of long-chain fatty acids of the omega-3 type. Use of the omega-3 fat has been associated with a decreased tendency towards blood clot formation, a reduction in blood triglyceride levels, reduced tumor growth, a reduction in blood pressure levels, an anti-inflammatory action and milder menstrual symptoms. Where can the vegetarian find omega-3 fat without having to eat fish or fish oil capsules? Flax seed is very rich in omega-3 fat, while other good plant sources include English walnuts, butternuts, soybeans, soy oil and canola oil. While vegetables have little fat content, the fat they do contain is very high in omega-3.
Present consensus is that too much polyunsaturated fat in the diet (levels above 7 percent of the total calories) is not the healthiest. Hence, the oils rich in monounsaturated fats (such as olive, canola and almond oils) have recently become popular. Other foods rich in "mono" fat include avocados, pistachios and pecans. One should note that all plants oils that are rich in either polyunsaturated or monounsaturated fat can significantly lower blood cholesterol levels.
Moderate to high intakes of trans fatty acids can elevate blood cholesterol levels (similar to the action of saturated fat) while lowering blood levels of HDL - the good cholesterol. However, recent studies of patients who had heart attacks or who died of heart disease, did not reveal levels of trans fatty acids in their body any different from persons free of heart disease. Apparently, the average intake of trans fat isn't great enough to cause a serious health risk. Nevertheless, some have steered away from margarine because of its trans fat content. However, butter is not a better alternative since two-thirds of its fat is saturated fat. Butter also contains over 60 mg cholesterol/oz. On the other hand, margarine contains up to 10 times more of the antioxidant vitamin E than butter.
Compared with animal fat, the use of vegetable oil is associated with a lower risk of chronic diseases. Obtaining oil naturally from grains, nuts and seeds is preferred to the refined oil from those products since the grains, nuts and seeds provide protein, vitamins and minerals as well as fat.
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In a Japanese study, the daily intake of green-yellow vegetables was associated with a significant 26% reduction in the risk of death from total stroke in men and women compared with an intake of once or less per week. Daily fruit intake was associated with a significant 35% reduction in risk of total stroke in men and a 25% reduction in women.