Apparently, this is a messy topic.
Honestly, I use ALOT of sweeteners, primarily aspartame. And I just researched this to confirm my assumption that this was all hogwash, I mean, no calories=no calories. A sweetener is not sugar.
Yet, the media got ahold of this topic and paraded around the flashy headline, "Sweeteners linked to Weight gain, Not weight loss."
However, the operative word here is "linked." The msm seems to have, as they fucking always do, distorted the actual findings to present a flashier news report.
The title suggests that the studies found that sweeteners were CAUSALLY linked to weight gain, whereas the studies only demonstrated that the two were CORRELATED. They suggested that sweeteners make people desire sweeter foods or that people who use sweeteners believe that by using sweeteners, this allows them to gorge on other sweets (recall that one Family Guy clip of an obese girl taking a sip of a Diet Dr.Pepper then declaring, "Now I can eat anything!"
As for the blood sugar, there seems to be evidence that sweeteners raise blood sugar levels. (
Could Artificial Sweeteners Raise Your Blood Sugar?). Though I don't know what other physiological effects this would entail.
All in all, it doesn't seem likely that one sugar-free monster a day–in my opinion, after just reviewing the literature–would have any noticeable effect on your physiology.
I myself use aspartame quite heavily, so it's possible my conclusion may be a product of motivated reasoning. Nevertheless, there are plenty of articles on this that you can review for yourself.
Hope this helps,
Cheers