Protein can cause a spike in Insulin, but not aspartame. Furthermore, consuming aspartame with or without carbohydrates resulted in aspartame not contributing to an insulin spike.
Diabetics were found to have no spike in insulin after ingesting nonnutritive sweeteners. Swishing a solution in the mouth had no effect
About the only study suggesting sweeteners could spike insulin was found in vitro rat pancreatic cells when coupled with glucose and done with direction transfusion (instead of ingested orally)
the data from extensive in vivo studies in human subjects show that low-energy sweeteners do not have any of the adverse effects predicted by in vitro, in situ or knockout studies in animals. 
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"Do artificial sweeteners spike insulin?," Examine.com, published on 10 February 2012, last updated on
10 February 2012,