Kenneth Gardner
OUR BODY synthesises cholesterol naturally because it is essential in the formation of bile acids which we use in fat digestion. Cholesterol is also an essential component of cell membranes, and is found in large amounts in the brain and nerve tissue. Cholesterol is found in all animal foods, especially egg yolk and organ meats such as liver and kidney which have very high levels of it. It is also found in every cell of the body, has very important physiological functions and is transported, along with other fat material, in blood.
To transport the cholesterol and fat material, the body utilises different protein packets. The fat protein particle that results is called a lipoprotein. Lipoproteins vary in their ability to transport cholesterol; the low-density lipoproteins are the major carriers of cholesterol. The protein part of the lipoprotein is called apoprotein and carries the lipids in the blood. Apoproteins are very important in activating or inhibiting certain enzymes involved in the metabolism of fats. The apoprotein in high-density lipoprotein (HDL) (sometimes called the good cholesterol) act as a type of shuttle as it takes up cholesterol from the blood and body cells, and then transfers it to the liver where it is used to form bile acids. Some of the bile acids that are involved in the digestion process are passed out with the stool, thus providing the body with its major way of eliminating cholesterol. HDL is sometimes referred to as the 'garbage truck' of the blood system as it collects cholesterol and dumps it in the liver.
BUILD-UP OF ATHEROSCLEROSIS
High amounts of HDL cholesterol have been found to be associated with low heart disease risk. Low-density lipoprotein (LDL, the bad cholesterol) have very high levels of cholesterol that are involved in cell functions that contribute to the build-up of atherosclerosis. Investigations have shown that persons who participate in vigorous endurance-type exercise generally have plasma lipid and lipoprotein profiles consistent with lower risks of coronary heart disease. Endurance exercise that uses about 1,000 kilocalories for the week at a moderate intensity is about all it takes to produce the plasma lipid or lipoprotein changes. Higher levels of energy expenditure up to 4,500 kilocalories per week have produced excellent results.
Decreases in total cholesterol and LDL cholesterol with exercise are greater when persons also lose weight. The effects of weight loss and increased aerobic exercise are additive in improving the levels of HDL to LDL. High-density lipoprotein is assembled in the plasma from precursors from the small intestine, liver and other circulating lipoproteins. The protein, lipoprotein lipase, an enzyme in the capillary walls of muscle and fat tissue, breaks down the materials in the circulating lipoproteins and allows the body cells to take in the fatty acids to increase energy production.
EXERCISE LINKED TO ELEVATED LEVELS OF HDL
Physically-active persons who do regular aerobic exercises can have up to double the normal lipoprotein lipase activity in their muscle and adipose tissue, so the muscles can use more fatty acids for fuel. Enzymes in the liver of active persons also utilise more of the cholesterol from the tissues and other circulating lipoproteins to form bigger HDLs. Similarly, enzymes in the cells surrounding liver capillaries irreversibly remove HDL particles from the blood.
Numerous studies have found that exercise is linked to persons having elevated levels of HDL. This prevents the narrowing of the arteries that leads to heart disease. The famous Farmingham Heart Study referred to persons with very high levels of HDL as having the 'longevity syndrome' because they tended to live into their 80s and 90s without heart disease. So exercise regularly and reduce your cholesterol.
Kenneth Gardner is an exercise physiologist at the G.C. Foster College of Physical Education; email: yourhealth@gleanerjm.com.
