Exercise and Blood Lipid Levels
A person's total cholesterol has a direct correlation with the presence of very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL). These lipid-carrying substances are responsible for transporting cholesterol and triglycerides, which are fatty acids, throughout the body. A healthy cholesterol level is one consisting of a lower presence of VLDLs and LDLs and a higher presence of HDLs. Because VLDLs and LDLs transport and deposit excess cholesterol around the walls of arteries, they are known as the "bad" cholesterol. Conversely, HDLs, which pick up and transport excess cholesterol back to the liver, are known as the "good" cholesterol. Exercise is known to increase the number of HDLs, thus improving cholesterol levels.
Exercise for the "Good"
In men, endurance exercise intensity around 75 percent of maximum output appears to be the ideal level needed to increase the levels of HDLs in the body. In women, both pre- and postmenopausal, it has been established that lower intensity, longer bouts of endurance training produces more HDLs. The intensity of exercising is important because it dictates what fuel substrate the body opts for in energy utilization. If intensity is too high, the presence of oxygen will be low, forcing the body to turn towards carbohydrates in the form of glucose for energy. This point is evident when breathing during a bout of exercise becomes labored. Carbohydrates are the only fuel source that can be metabolized without the presence of oxygen. Therefore, maintaining an exercise intensity below maximal output encourages lipid metabolism, which occurs in the liver. This facilitates the need for the production of HDL to return cholesterol and fat to the liver.
Maintaining a Healthy Heart
Exercise enhances the production of enzymes that facilitate HDL transportation of cholesterol back into the liver to be broken down. Although the precise volume and frequency necessary to enhance HDL presence and performance have not been quantified, it is best to incorporate endurance exercise consistently on most days of the week. Regular exercise in excess of 30 minutes is generally recommended for a healthy heart. Resistance or weight training has shown to have a minimal impact on blood cholesterol levels.
References
- Durstine, J.L. and W.L. Haskell. 1994. Effects of exercise training on plasma lipids and lipoproteins. Exercise and Sports Science Reviews. 22:477-522.
- Sports and Fitness Nutrition. Wildman, Robert and Miller, Barry. 2004
