Speaking of filler, it seems the experiment in question didn’t control for that? Since there’s so little artificial sweetener is it possible the gut flora are reacting to the filler?
The experiment in the article explicitly does control for this
> The participants (20 per group) were given sweetener packets of aspartame, sucralose, saccharin, or stevia, each bulked out with glucose to an equivalent size, with another group that got just glucose and another group that took no sweeteners at all.
In this experiment, the artificial sweeteners used glucose as the filler. They also account for the effects of the glucose filler on the insulin response in all groups by measuring the difference in the response.