LDLs, HDLs, and TC: Cholesterol is a waxy, fatlike substance found in all animal products (meats, dairy products, and eggs). The body can make cholesterol in the liver and absorb it from the diet. Cholesterol is essential to the body, and it is used to build cell membranes, to produce sex hormones, and to form bile acids necessary for fat digestion. Lipoproteins are an essential part of the complex transport system that exchanges lipids among the liver, intestine, and peripheral tissues. Lipoproteins are classified by the thickness of the protein shell that surrounds the cholesterol. The four main classes of lipoproteins are chylomicron, derived from the intestinal absorption of triglycerides (TG); very low-density lipoprotein (VLDL), made in the liver for the transport of triglycerides; low-density lipoprotein (LDL), a product of VLDL metabolism that serves as the primary transporter of cholesterol; and high-density lipoprotein (HDL), involved in the reverse transport of cholesterol to the liver. The molecules of LDL are larger than those of HDL and therefore precipitate in the plasma and are actively transported into the vascular walls. Excess LDL-cholesterol (LDL-C) stimulates the formation of plaque on the intima of the coronary arteries. Plaque formation reduces the cross-sectional area and obstructs blood flow in these arteries, eventually producing a myocardial infarction. Therefore, LDL-C values less than 100 mg.dl-1 are considered optimal for reducing CVD and CHD risk. The smaller HDL molecules are suspended in the plasma and protect the body by picking up excess cholesterol from the arterial walls and delivering it to the liver where it is metabolized. Individuals with low HDL-C or high TC levels (dyslipidemia) have a greater risk of heart attack. Those with lower HDL-C (<37 mg.dl-1 ) are at higher risk regardless of their TC level. This fact emphasizes the importance of screening for both TC and HDL-C in adults. Physical Activity and Lipid Profiles: Regular physical activity, especially habitual aerobic exercise, positively affects lipid metabolism and lipid profiles. Cross-sectional comparisons of lipid profiles in physically active and sedentary women and men suggest that physical fitness is inversely related to TC and the TC/HDL-C ratio (Shoenhair and Wells 1995). The research on the effect of resistance training on cholesterol levels continues to remain inconclusive.
- Protestant Mezmur