Metabolism of substrates: diet, lipoprotein metabolism, and exercise.

The major classes of serum lipoproteins have been shown to be differentially affected not only by dietary factors but also by levels of physical activity. Individuals engaging in relatively higher amounts of physical activity tend to have lower levels of low-density lipoprotein cholesterol (LDL-C) and very-low-density lipoprotein cholesterol (VLDL-C) and higher levels of high-density lipoprotein cholesterol (HDL-C) than their sedentary counterparts. However, higher levels of physical activity are also associated with lower adiposity and elevated caloric intake, two factors that themselves have independent roles in the regulation of lipoprotein levels. Changes in adiposity appear to be responsible for some, but not all, of the lipoprotein change associated with exercise. A study in which 14 sedentary, middle-aged men engaged in a progressive running program over 2 years showed increased HDL-C and decreased LDL-C, both considered antiatherogenic. Adiposity, expressed as percent body fat, decreased during the study whereas caloric intake, notably in the form of carbohydrates, increased. Elevated physical activity levels alter the relationships among adiposity, dietary intake, and lipoproteins that prevail in the sedentary state.