Natural Fat Yes, Added Fat No
By Donald R. Davis, Ph.D.
We all get daily messages -overt and subtle-that dietary fat is bad. Low-fat foods are in, and high-fat foods like nuts and avocados are out, at least until recently. Junk foods carry proud “low fat” labels. Some experts recommend avoiding fatty fish. Markets offer low-fat peanut butter and tofu.
We must learn to strongly distinguish between fat that is naturally present in foods -” and fat that humans add.
Dietary fat has a bad reputation because worldwide fat intakes often (but not always) correlate with heart disease, cancer, and obesity. Some fats, and especially saturated fats, raise blood cholesterol levels. Weight-conscious Americans are impressed to learn that fat carries twice the calories of carbohydrate and protein.
The low-fat message is so common and long-standing that the case against dietary fat is widely accepted as beyond dispute. Partly it is, but we must modify the message, because it is seriously oversimplified and partly wrong. In fact, it harms efforts to prevent the very problems it was intended to help heart disease, obesity, cancer, and others.
We must learn to strongly distinguish between fat that is naturally present in foods and fat that humans add. There is much evidence that nuts, peanut butter, avocados, fatty fish, and tofu actually help prevent and cure heart disease and obesity, if not cancer.
We should eat more of these foods, not less. Yet there remain good reasons to reduce or avoid added fats. Added fats include all vegetable oils, vegetable shortening, margarine, butter, and lard. They supply roughly half of the fat that Americans eat. The old message still applies to these fats, though to some more than others.
Heart disease has the best evidence favoring fats from natural fat sources. Over a dozen studies find that eating various nuts, peanuts, or avocados, or preferably substituting these for added fats, improves blood lipids. More importantly, these foods greatly reduce the risk of heart disease.
What about obesity? Americans on average have reduced their fat intake over the last 20 years. Many experts expected obesity to decline, but instead it surged. Two studies show that nuts and avocados, at least, improve weight loss diets, despite the higher calorie content of fat. Low-fat diets usually ”work” initially, but seldom for long, as the diets are not well sustained. Also, they often raise blood triglycerides (fats). With nuts or avocados added, triglycerides drop, people feel less hungry or deprived, and long-term results improve. That finding suggests that nuts and avocados might help prevent weight gain in the first place.
Breast cancer is very low in countries where fat intakes are low, relative to the U.S. and other countries with high fat intakes. This correlation never proved that fat causes breast cancer, but that conclusion was widely accepted. No longer. Harvard researchers found that low-fat American diets show not even a hint of preventing breast cancer.
What is wrong with added fats? Nearly “empty calories,” for starters. Unlike added fats, nuts,avocados, fish, tofu, and all other natural fat sources are rich in many nutrients and phyto-chemicals (except fish). They also have structure, protein, fiber (usually), flavors, water, and other substances that limit their palatability and consumption, unlike added fats that pour or spread and require no chewing. These same factors also slow fat absorption. With carbohydrates, we value slow absorption as measured by a low “glycemic index” (low impact on blood sugar). One day we may similarly value slow absorption of fat, measured by a low “lipemic index” (impact on blood lipids). Finally, partially hydrogenated fats like stick margarine and vegetable shortening have these disadvantages, plus one more. They contain trans fatty acids and other unnatural molecules that interfere with natural fat functions and disrupt hormone-like prostaglandins. Some countries ban such fats, and prominent researchers call for the U.S. to follow their lead.
Are meats natural sources of fat? Yes, if animals are raised on natural diets. Unfortunately, grain-fed beef, pork, and chicken have about triple the fat of their naturally fed kin, and the ratios of omega-3, omega-6, and saturated fats are much harmed. It makes sense to remove most of the fat from grain-fed meats, and to be sure to get omega-3 fat from other sources such as fish, walnuts, and tofu (not the low-fat kind!). The fat in fish is much less affected by farming methods.
Look for ways to use more natural fat sources and less added fats. Eat nuts and oily seeds plain, with fruit, on cereal, in vegetable dishes, and on pasta. On bread try peanut butter, other nut butters, and cheese instead of butter. (“Old-fashioned” peanut butter is not partially hydrogenated.) Use nuts, avocados, and cheese on salads instead of oily dressing. In sandwiches use avocados or cheese in place of mayonnaise.
The fat story resembles the sugar story. We enjoy and seek sugar, because natural sources of sugar build health (fruits, berries, melons, and sweet vegetables). The problem with sugar is added (refined) sugar, which does not build health, especially in the large amounts that refining enables. We don’t discourage fruit because of its sugar. We shouldn’t discourage nuts, avocados, tofu, or fish because of their fat.
Fat is clearly part of Nature’s plan for children. Breast milk has more fat than whole cow’s milk, and pediatricians no longer advocate lowfat milk for children. Early this year the American Diabetes Association (ADA) began recommending high mono-unsaturated-fat diets for diabetics (nuts, avocados, peanuts, and olive oil), an alternative to its previous low-fat advice. Such diets improve “HDL cholesterol, triglycerides, and most importantly, diabetes control.” The ADA also advised against partially hydrogenated fats.
To sum up, we badly need to distinguish between natural sources of fat and added fats, especially added fat that is partially hydrogenated. The daily messages should not be “low fat,” but “low added fat.” Three words instead of two. It shouldn’t be that hard to make a big step toward better health.
We also need to remember that there is more to good nutrition than fat. Junk foods can be “low added fat,” and still contribute nothing to our health.