Insulin resistance causes a number of detrimental metabolic changes to energy and appetite regulatory systems that results in weight gain, particularly in the viscera of the abdomen. The aetiology of insulin resistance in not fully understood, but is thought to result from defects to the insulin receptor substrate-1 (IRS-1) protein, and its downstream signal cascade, perhaps through free radical or lipid induce mechanisms. A number of strategies have been investigated to reverse insulin resistance and of these the use of antioxidants and exercise are two of the most well studied. Animal and human studies show that supplementation with antioxidants, or consumption of diets high in antioxidant nutrients, provides an insulin sensitising effect. Likewise, data from both animal and human studies attest to the effectiveness of exercise at improving insulin sensitivity. However while antioxidant therapy and exercise are effective, combinations of the two may provide superior benefits when compared to either strategy alone.
For example, animal studies have been used to assess the effects of antioxidants and exercise on changes to insulin sensitivity. In one study1, researcher used R-alpha lipoic acid (R-ALA) to reverse insulin resistance in a rat model of obesity. Alpha lipoic acid is an endogenously produced antioxidant which has been shown to reduce oxidative stress in animals and humans when administered as a supplement. The same researchers also were able to reverse insulin resistance in the obese rat model when they forced the animals to run on treadmills. Exercise is likely effective at at reversing insulin resistance because it causes the oxidation of fatty acids in the peripheral tissues and fatty acids may interfere with the insulin signal cascade when they accumulate in skeletal muscle and liver tissue. Antioxidants may reverse insulin resistance through a different mechanism to exercise, perhaps by prevention of free radical interference with intracellular insulin signalling.
When given together it might therefore be expected that antioxidants such as R-ALA and exercise may have synergistic effects. In fact, this is exactly what is observed. Supplementation of obese rats with R-ALA and use of an endurance exercise protocol in combination produced an insulin sensitising effect greater than R-ALA or exercise alone. The ability of exercise to cause weight loss is often ascribed to its potential to cause an energy deficit. However, the insulin sensitising effects of exercise are a more logical and scientifically supported reason for this weight loss effect. That low plasma levels of antioxidants are associated with obesity also supports evidence to show that antioxidants have insulin sensitising effects. While R-ALA was the antioxidant used in this study, other antioxidants may be just as effective. Likewise, endurance exercise might not be the only form of exercise to cause increases in insulin sensitivity, as evidence suggest that resistance training may have superior effects.
RdB
