Has anyone found that the sweeter a protein powder is, the less fat you lose during a diet that relies heavily on protein powder (e.g. the Velocity Diet)? Do the artificial sweeteners in protein powders create havoc with insulin levels?
Sucralose or Aspertame
That has been discussed and rejected many, many and many times already.
The sweet taste during cephalic phase of digestion is unable to generate changes in insulin production.
American Journal of Clinical Nutrition, Vol 65, 737-743,
Cephalic phase responses to sweet taste
L Abdallah, M Chabert and J Louis-Sylvestre
Laboratoire de Neurobiologie de la Nutrition, Ecole Pratique des Hautes Etudes, Paris, France
Beyond that, there are links of some sweeteners to increased hunger but it has been shown that while increase hunger is possible, it has not been liked to any increase in bodyweight gain in humans and was reported to have no impact on food intact and even possible reduction.
So it is probable that what you observe is due to other causes, maybe your less sweetened proteins taste like crap and you drank less of them reducing calories further or maybe they were of low quality and they put real sugar in them.
Considering that we can't easily test for the presence sugar within our protein (which I assume you mean no-carb proteins, like Metabolic Drive), we'd have no way of finding the amount of sugar in them unless you checked your glycemia a couple of times every time you take your shakes with a control situation where you would drink only a known amount of protein (like the one in the protein shake)with various amounts of sugar and check for matching levels. Then again, this is purely hypothetical since we don't have access to just the pure protein anyway.
That is why you rely on ''trusted'' providers of protein like Biotest.