Macronutrients in Health and Disease: Fats

Foods contain combinations of saturated and unsaturated fats*. Saturated fat is found in high quantities in dairy products, eggs, and meats, for example, while vegetable oils are particularly high in unsaturated fats. Unsaturated fats are either monounsaturated (found in olive and canola oils) or polyunsaturated (found in nuts, seeds, and seed oils).

Only two kinds of fats are essential, and both of these are polyunsaturated. They have important roles as parts of cell membranes and as signaling molecules. The essential fatty acids include linoleic acid (an omega–6 fatty acid) and alpha–linolenic acid (an omega–3 fatty acid). They are called “essential” because they are not produced by the body and must be obtained through the diet or supplementation.

Essential fatty acids are converted into hormone–like chemicals called eicosanoids. These chemicals play significant roles in the immune system, inflammation, blood clotting, and many other functions. A healthy balance of eicosanoids occurs when a relatively large amount of omega–3 fats is consumed, compared with omega–6 or other fats. Typical Western diets, however, tend to provide significantly more omega–6 fats and far fewer omega–3 fats. This imbalance is commonly seen in several diseases, including heart disease and asthma, and may contribute to the disease process. Reducing the intake of omega–6 fatty acids and saturated fats (particularly in animal products) results in an improved balance of eicosanoids.

The Need to Limit Fat

Of all the macronutrients, fats have the greatest potential to cause disease when consumed in excess. Reducing fat in the diet is helpful for reducing excess weight. Fat provides 9 calories per gram, more than twice the number of protein or carbohydrate, and individuals who successfully maintain a significant weight loss typically eat less than 25 percent of calories from fat. Reducing saturated fats, in particular, is important in controlling cholesterol levels.

Generally speaking, fatty foods provide few nutrients. Other than essential fatty acids, vegetable oils provide vitamins E and K, which can be obtained from other sources. Ideally, fats should not be added to meals; rather, they should be consumed in modest amounts as part of healthy foods that provide essential nutrients. For example, nuts provide essential fatty acids along with magnesium, copper, folic acid, potassium, fiber, and vitamin E.

The National Academy of Sciences Food and Nutrition Board currently recommends that 20 to 35 percent of caloric intake come from fat, although this is controversial, given that people who eat significantly less fat have excellent health, if not better than people eating more fat. Most individuals can meet their needs for essential fats by eating only small amounts (about 14 grams per day) of fat. However, most Americans are eating far more than that amount (around 85 grams per day, on average).