Objective: To assess whether shortening of the corrected QT (QTc) interval is most closely associated with changes in weight, insulin resistance, or free fatty acids (FFAs) (or some combination of these factors).
Methods: We randomized 75 severely obese subjects without diabetes to either a low-carbohydrate or a conventional low-fat weight-loss diet for 6 months. We measured QTc, insulin sensitivity, body mass index, and FFAs at baseline and at 6 months. Analysis was performed to determine whether improvement in weight, in insulin resistance, or in FFAs has the greatest effect on reducing the QTc interval.
Results: "Completers" of both the low-carbohydrate diet (N = 25) and the low-fat diet (N = 22) had a decrease in weight, but the weight loss was greater in the low-carbohydrate group. A statistically significant decrease in QTc from baseline was observed only in the low-carbohydrate group. QTc in the low-carbohydrate group correlated with improvement in insulin resistance, but this finding was not significant after correction for the greater weight loss. FFAs or weight loss was not correlated with QTc in either dietary group.
Conclusion: Low-carbohydrate dieting is associated with a greater decrease in the QTc interval in comparison with low-fat dieting. Improvements in insulin resistance seem to have a relatively weak mechanistic role, and a decrease in FFAs has no apparent role in the reduction of the QTc interval.