According to the USDA, a low-fat diet as the name implies is a diet that consists of little fat, especially saturated fat and cholesterol, which can lead to increased blood cholesterol levels and heart disease risk. It is imperative to know that some dietary fat is needed for good health though: fats supply energy and essential fatty acids, in addition to further enhancing the absorption of some fat-soluble vitamins like A, D, E, and K.

However, in recent years the exact health benefits of a low-fat diet have been debated. A 2006 study published by the Journal of the American Medical Association argued that a low-fat diet did not reduce the incidence of breast cancer. However, this study was criticized by several epidemiologists for its lack of validity (see "Criticisms" in the Women's Health Initiative article). Recently, the Nurses' Health Study from the Harvard School of Public Health reported from a Dietary Approaches to Stop Hypertension (DASH), and found that a diet "with high intake of fruits, vegetables, and whole grains, moderate intake of legumes, nuts, and low-fat dairy products, and low intake of red and processed meats and sodium, was significantly associated with lower risk of coronary heart disease and stroke in women." A 2002 Cochrane Review found low-fat diets to be no more effective than other weight loss diets in achieving lasting weight loss.