Low-Fat Diets

A typical American diet contains somewhere between 35 to 40 percent of calories from fat. The 2005 U.S. Department of Agriculture (USDA) Dietary Guidelines for Americans recommend that healthy adults keep total dietary fat intake between 20 to 35 percent of calories from fat. They define low fat intake as no more than 20 percent of calories from fat. There are many different types of low-fat diets, each with their own benefits and drawbacks. Studies show that low-fat diets may reduce the risk of coronary heart disease and may help people lose weight.

[Page 437]Dietary fat is an essential macronutrient that supplies energy and essential fatty acids and acts as a carrier for fat-soluble vitamins such as A, D, E, and K. Fat provides 9 calories per gram which is more than twice the caloric density of carbohydrates or protein. In adipose (fat) tissue, it serves as an important energy storage source. When the body has depleted energy from carbohydrates, it begins to burn fat in a process called fatty acid oxidation. This occurs during long fasts and after about 20 minutes of exercise.

Certain segments of the population need to consume a low fat diet due to health concerns. These groups include people with gallbladder disease, fatty liver, fat absorption disorders, and fatty acid oxidation disorders. People with elevated cholesterol, hypertension (high blood pressure), and/or a history of heart disease are advised by the American Heart Association (AHA) to reduce saturated fat and cholesterol intake and keep total fat intake below 30 percent of total calories.

There are several popular low-fat diets, many of which have been around for decades. Vegan, vegetarian, and macrobiotic diets are plant-based diets that are usually low in fat because most animal products are avoided, but they do not intentionally restrict calories from fat. Very low-fat diets (no more than 15 percent calories from fat) have been criticized as being “too restrictive” and depriving the body of essential fatty acids like omega-3 polyunsaturated fatty acid. It is possible that intake of large amounts of fiber from very low-fat diets diet could cause gastrointestinal distress such as diarrhea. Also, very restrictive diets are difficult to maintain for Americans who travel often and frequently eat out at restaurants. However, low-fat diets have documented clinical studies showing reversal of coronary blockage and weight loss. They are one of the few popular diet plans with a strong scientific basis.

The Ornish Diet is a well-known and well-studied very low fat diet. Dean Ornish is a cardiologist who is Clinical Professor of Medicine at the University of California, San Francisco. He created the Ornish Lifestyle Modification Program, based on: (1) a very low fat, high complex carbohydrate diet rich in fruits, vegetables, whole grains, beans, and legumes, (2) regular exercise, (3) stress management, and (4) family/community support systems to maintain desired healthy behaviors. The Ornish Diet restricts fat intake to 10 percent of total calories and promotes consumption of complex carbohydrates. According to Ornish's book Eat More, Weigh Less, the typical American diet contains 40 percent calories from fat, 20 percent from protein, and 40 percent from carbohydrates. Ornish recommends eating beans, fruits, grains, and vegetables whenever you are hungry. Nonfat dairy products, egg whites, and nonfat processed foods are allowed in moderation. Foods to be avoided include simple sugars, alcohol, meats, oils, avocados, olives, nuts, seeds, fat-containing dairy products, and any processed food containing more than 2 grams of fat per serving.

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