A low-fat diet is one that restricts fat and often saturated fat and cholesterol as well. Low-fat diets are intended to reduce diseases such as heart disease and obesity. Reducing fat in the diet can make it easier to cut calories. Fat provides nine calories per gram while carbohydrates and protein each provide four calories per gram, so choosing low-fat foods makes it possible to eat a larger volume of food for the same number of calories. The Institute of Medicine recommends limiting fat intake to 35% of total calories to help prevent obesity and to help control saturated fat intake.
Studies on the benefits of a low-fat diet have given mixed results. Many studies show that reducing fat intake leads to reductions in caloric intake, resulting in weight loss or less weight gain. Low-fat diets have been promoted for the prevention of heart disease. Lowering fat intake from 35-40% of total calories to 15-20% of total calories has been shown to decrease total and LDL cholesterol by 10 to 20%; however, most of this decrease is due to a reduction in saturate fat intake. Saturated fat has been shown to raise total and LDL cholesterol in a large number of studies and has also been correlated with a higher risk of heart disease. Furthermore, a high-fat diet can contain "unacceptably high" amounts of saturated fat, even if saturated fats from animal products and tropical oils are avoided. This is because all fats contain some saturated fatty acids. For example, if a person chose fats with only 20% saturated fatty acids, setting fat intake at 35% of total calories would mean that 7% of calories would come from saturated fat. For this reason, the Institute of Medicine recommends consuming no more than 35% of calories from fat.
While low-fat diets lower total and LDL cholesterol, a sudden increase in carbohydrate has been "consistently" shown to raise triglycerides. Increasing the carbohydrate content of the diet gradually has been shown to prevent hypertriglyceridemia.
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