Research has expanded our understanding of the effects of dietary fats on our health. However, changes to the food supply and to food processing methods have made it difficult to apply this research to patient care and the health of the general population.
In this issue of American Family Physician, White categorizes fatty acids and reviews evidence of the clinical implications of the type and amount of fat in our diets.1 A large body of evidence indicates that saturated fats and trans fats increase levels of low-density lipoprotein cholesterol and total cholesterol, as well as increase the risk of cardiovascular disease (CVD) and certain cancers. Trans fats also reduce high-density lipoprotein cholesterol levels. Additionally, recent studies have shown that diets high in saturated fat increase insulin resistance.2 A limited number of randomized clinical trials show that replacing saturated fat intake with a lower total fat intake or a higher intake of unsaturated fats reduces the risk of CVD.1,3–5
Several organizations, including the American Heart Association (AHA),6 the National Institutes of Health (NIH),7 and the Institute of Medicine,8 have recommended a moderation in fat intake that focuses on the quality of fat ingested. The AHA and the NIH recommend a total dietary fat intake between 25 and 35 percent of a person's daily calories, with saturated fats and trans fats limited to less than 7 and 1 percent of daily calories, respectively. Current daily intakes in the United States range from 10 to 12 percent of calories for saturated fats and 2 to 3 percent for trans fats.6
Trans fats are found in the hydrogenated oils often used in convenience foods, baked goods, and commercially fried foods. Many manufacturers have removed trans fats from their food, but some have increased the saturated fat content to maintain the desired taste and consistency. Patients can limit their intake of trans fats by substituting liquid vegetable oils or tub margarines for hydrogenated fats (e.g., stick margarines, shortenings), and by reducing their consumption of processed foods. It is important to remind patients that although a food may be free of trans fat, it may still be a source of empty calories.
Although trans fat has received much attention recently, saturated fat has a greater impact on the risk of CVD because it makes up a larger proportion of Americans' diets. The major sources of saturated fat are animal products (i.e., high-fat meat, high-fat dairy products) and tropical oils (i.e., palm oil, coconut oil). To reduce saturated fat intake, physicians should encourage patients to eat low-fat or skim dairy products, lean meats, poultry without skin, fish that has not been fried, and at least one to two meals per week based on vegetable proteins (e.g., legumes, soy protein).
Dairy products do not need to be eliminated from the diet, because skim or low-fat products are an excellent source of calcium and protein without excess saturated fat. Similarly, not all red meats need to be avoided, because 3- to 4-oz servings from the loin of pork or beef (e.g., tenderloin, loin chops, top sirloin steak) are nearly as low in saturated fat as the dark meat of poultry. At one point, tropical oils had nearly disappeared from processed food, but they have recently returned as food manufacturers look for trans fat replacements. Patients should be encouraged to read food labels, which are required to list saturated fat and trans fat content. Additionally, most fast food restaurant Web sites provide nutrition information, including saturated fat and trans fat content. Patients can use this information when choosing a restaurant or ordering a meal.
Heart-healthy eating involves more than limiting consumption of saturated fats and trans fats. Although there have been conflicting reviews about the benefits of omega-3 fatty acids, some trials of omega-3 fatty acids and omega-3 fatty acid supplements in healthy diets have demonstrated improved clinical outcomes.3–5,9 The Lyon Heart Study found that patients with CVD who consumed diets moderate in total fat; lower in saturated fats and trans fats; higher in omega-3 fatty acids; and higher in vegetables, fruits, whole grains, nuts, and legumes had a significant reduction of CVD events and mortality.5
The challenge in clinical practice is to routinely provide nutrition assessment and education to help patients make lifestyle changes. Physicians should learn effective counseling techniques to improve patient adherence and outcomes.10