The ingredient Truvia mixes it's Stevia with it Erythritol. You might check to see if your Pure Stevia is truly 100% Stevia or mixed with another -ol rather than Erythritol. One benefit of erythritol is that, because most of it is absorbed by the small intestine it does not typically cause some of the unfortunate laxative effects that are associated with other sugar alcohols.
Erythritol is also considered a natural ingredient as it is found naturally in some fruits and other foods.