Fat Intake

The role of dietary fat and its effect on human adiposity has been controversial for some time. Low-fat and very-low-fat diets were thought to reduce the percentage of body fat in the past. More recently, popular high-fat diets were found to have a similar effect. The growing obesity epidemic along with confusing information regarding fat intake recommendations for weight loss and weight maintenance has led to a renewed interest into the role that dietary fat plays. Recent research suggests that a low fat (about 20 percent of calories from fat) to a moderate-fat diet (about 35 percent of calories from fat), has little to no effect on the percentage of body fat as has been observed long term.

Dietary fat supplies about nine calories per gram, which is more than twice the amount of energy that is found in carbohydrates and proteins. Low-fat diets have been recommended, because of fat's higher energy density, as a preferred way to reduce the amount of total calories consumed. However, many foods containing moderate to high amounts of fat may lead to greater satiety, and consequently reduced food consumption.

Dietary fats are essential to many biological functions and are an integral part of cell membranes. In addition, essential fatty acids from dietary fats are needed in the absorption of the fat-soluble vitamins A, D, E, and K as well as in the absorption of carotenoids. Dietary fats occur naturally as saturated, monounsaturated, and polyunsaturated fatty acids. Trans fatty acids are unsaturated fatty acids, which have been chemically altered to become partially hydrogenated. Cholesterol, even though not a fatty acid, is a fatty substance essential in many biological pathways. Cholesterol is synthesized in the liver as well as obtained through animal sources in the diet.

While fat is important to a balanced diet, ingesting too much fat can have dramatic and serious health effects.

Saturated fat, which is predominantly found in animal products, and trans fats, which are frequently used in vegetable shortenings, cookies, and snack foods, has been linked to an increase in LDL-cholesterol levels. Elevated LDL cholesterol is frequently associated with obesity, and may increase the potential for coronary heart disease. As a general guideline, the fat intake from saturated fat should be less than 10 percent of the total caloric intake, with energy from trans fats reduced to a minimum and a dietary cholesterol intake of less than 300 milligrams/day. Some [Page 266]research suggests even lower intakes of saturated fat and cholesterol to treat adults with elevated LDL cholesterol levels. Foods high in saturated fats are usually solid at room temperature and include, for example, cheese, whole-milk products, beef, as well as fried foods, butter, ice cream, and desserts.

The main source of calories from fat should come from polyunsaturated and monounsaturated fatty acids, which are generally liquid at room temperature. Good sources of monounsaturated fatty acids include vegetable oils, such as olive and canola oil, as well as nuts. Evidence exists that a Mediterranean-style diet, which is high in monounsaturated fatty acids, may be effective in reducing the prevalence of the metabolic syndrome and its associated cardiovascular risk.

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