This study examined the effect of the antioxidant N-acetylcysteine (NAC) on acute insulin sensitivity after exercise in seven young, healthy participants. Moderate intensity aerobic exercise increases acute insulin sensitivity (Hawley & Lessard, 2008; Howlett et al., 2008) and recent evidence has suggested that regular antioxidant supplementation ablates the increase in insulin sensitivity seen through a structured exercise program (Ristow et al., 2009). This study thus seeks to test if an antioxidant can alter insulin sensitivity after a single bout of exercise. Seven untrained, healthy participants (22.1 ± 3.2 years of age, BMI: 24.8 ± 3 kg.m−2, VO2 peak, 50.6 ± 4 ml/kg/min) underwent a blind crossover study design, consisting of two identical trials separated by ∼14 days. In each trial NAC or saline was intravenously infused before and during sub-maximal exercise for a total of 95 minutes (62.5 ml/kg/min for 15 min, followed by 25 ml/kg/min for 80 min). During this infusion time, the participant underwent 35 minutes of passive rest, followed 60 minutes of sub-maximal exercise (55 min at 68% VO2 peak followed by 85% VO2 peak for five min) on an electronically braked cycle ergometer. After three hours rest, a hyperinsulinemic euglycemic insulin clamp was used to determine insulin sensitivity via a modified M-value (glucose infusion rate/ mean insulin concentration). NAC infusion during exercise resulted in ∼5.8% decrease in insulin sensitivity post-exercise (Figure, p = 0.041).
This research demonstrates that NAC alters insulin sensitivity after a single bout of intensified exercise. These data also suggest that reactive oxygen species produced during exercise have a role increasing post-exercise insulin sensitivity.
Hawley, J. & Lessard, S. (2008) Exercise training-induced improvements in insulin action. Acta Physiologica 192, 127-135.
Howlett, K., Mathews, A., Garnham, A. & Sakamoto, K. (2008) The effect of exercise and insulin on AS160 phosphorylation and 14-3-3 binding capacity in human skeletal muscle. American Journal of Physiology. Endocrinology and Metabolism 294, E401-7.
Ristow, M., Zarse, K., Oberbach, A., Klöting, N., Birringer, M., Kiehntopf, M., Stumvoll, M., Kahn, C. & Blüher, M. (2009) Antioxidants prevent health-promoting effects of physical exercise in humans. Proceedings of the National Academy of Sciences of the USA 106, 8665-70.