Wednesday, August 3, 2011

Exercise Power: what just one workout can do by Jerry Brainum

The Metabolic Syndrome is a cluster of medical symptoms estimated to affect 50 million Americans. The syndrome consists of elevated blood lipids, high blood pressure, a proinflammatory state, and a higher level of fat around the waist. These symptoms, in turn, are harbingers of cardiovascular disease and diabetes. Two of the earliest signs of the metabolic syndrome are insulin resistance and increased fat deposition in the liver, known as non-alcoholic fatty liver disease. The two conditions are related, and NAFLD is thought to be a primary cause of insulin resistance. NAFLD is now said to be epidemic, and if not treated, can lead to liver failure or even liver cancer. The question is: how can NAFLD and associated insulin resistance be effectively treated?
    One hint comes from a just published study that involved 12 young, lean men, average age, 23, who all had insulin resistance.While insulin resistance is usually associated with excess body fat, these men had average levels of body fat. Their insulin resistance was caused by defects in insulin-stimulated muscle glycogen synthesis caused by a lack of sufficient activity of glucose transporter proteins in muscle. What's interesting about these men is that they show the earliest sign of the metabolic syndrome--insulin resistance--without having any of the other symptoms of the disorder. As such, they are ideal subjects in which to study interventions that may prevent the onset of the metabolic syndrome and its associated diseases of cardiovascular disease and type-2 diabetes.
      The aim of this study was based on a hypothesis that skeletal muscle insulin resistance precedes liver insulin resistance. So the idea was to test the effects of a single session of 45 minutes on an elliptical machine, which would reverse skeletal insulin resistance. The men were studied at rest and after exercise. Before both, however, they ingested a carbohydrate meal (55% carbs) to follow the fate of the carbs. Would the carbs promote increased liver fat production, or be instead diverted to use for muscle glycogen synthesis?
    The results showed that after just one exercise session of 45 minutes, muscle glycogen increased three-fold over baseline. Along with this came a 45% reduction in the synthesis of liver fat following the high carb meal. The study clearly shows that if you correct skeletal muscle insulin resistance with exercise, it will reverse the insulin resistance that occurs in the liver, and leads to increased fat deposition in the liver.Since increased fat build-up in the liver is an early sign of the metabolic syndrome, this implies that you can prevent the onset of the metabolic syndrome by exercise. It also shows that carbs consumed prior to exercise, and immediately following exercise, are primarily used to replenish muscle glycogen stores, and are not used for purposes of  fat synthesis.
Rabel R, et al. Reversal of muscle insulin resistance with exercise reduces postprandial hepatic de novo lipogenesis in insulin resistant individuals.PNAS  2011: in press.

©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.

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