Artificial sweeteners may do more than sweeten tells that the sweetener sucralose affects the body more than just taste sweet. (Sucralose is the sweetener in Splenda. Aspartame is a different sweetener.)
In a limited test, researchers studied the effects of the sweetener on severely obese patients who did not have diabetes and also did not consume artificial sweeteners.
Surprisingly, when the test subjects drank products with sucralose prior to a glucose tolerance test, their blood sugar levels peaked at a higher level than with water.
This could mean that when artificial sweeteners are consumed, the body is producing more insulin than required. Too much insulin could result in resistance to insulin, which is the path to type 2 diabetes.
Prior to this study, it was believed that artificial sweeteners do not effect metabolism. Researchers suspect there are other sweetness receptors in the body besides those in the mouth. That would explain why the body produces the extra insulin.
Much of this is speculation - it was a very limited test and additional research is required.