LONG-TERM EFFECTS OF A HIGH-CARBOHYDRATE DIET AND EXERCISE ON INSULINACTION IN OLDER SUBJECTS WITH IMPAIRED GLUCOSE-TOLERANCE

Carbohydrate metabolism was assessed in 20 glucose-intolerant subjects before and after 12 wk on a high-carbohydrate diet (HC) or the diet c ombined with exercise training (HC-EX). The diet provided 60% of energ y as carbohydrate and 20% as fat. Neither treatment altered fasting gl ucose or insulin concentrations or their response to a meal. During a glucose clamp (216 pmol insulin/L) glucose disposal increased from 13. 2 +/- 0.83 to 14.6 +/- 0.83 mu mol . kg fat-free mass(-1) . min(-1) (P < 0.05) in both groups. During more pronounced hyperinsulinemia (654 pmol/L) glucose disposal did not change significantly (49.9 +/- 3.8 to 50.7 +/- 3.8 mu mol . kg fat-free mass(-1) . min(-1). Muscle glycogen increased in the HC-EX group (78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glu cose/kg muscle), with no changes in the HC group. These results do not support the recommendation to increase the dietary carbohydrate conte nt for improving postprandial glucose metabolism or insulin action in glucose-intolerant adults unless combined with exercise training, whic h promotes muscle glycogen storage.