Non-caloric sweeteners may interfere with normal glucose absorption.
A small study (published as an abstract) of healthy individuals received the equivalent non-caloric sweetener contained in 1.5 liters of "diet" soda for 14 days along with a with a control group receiving a placebo. The results suggest that glucose absorption is negatively affected in healthy people by artificial sweeteners. This early research may help explain why a population shift in the consumption of artificial sweeteners has not lowered type 2 diabetes risk.
PositiveTip: Limit both sugar-sweetened beverages and the "diet" drinks-- choose water instead!