Aspartame by itself does not move your blood sugar
Two reviews, one of 12 randomised trials and one of 100 controlled experiments, found no meaningful difference in glucose or insulin against a dummy drink.
What the study found
Blood sugar and insulin barely register aspartame
This is the sweetener on its own, not a whole diet drink. Two independent reviews, one pooling 12 randomised trials and one pooling 100 controlled experiments, found no meaningful difference in glucose or insulin against a dummy drink, and a smaller rise than sugar produces.
The caveat · 2025 review: certainty very low
The 2025 review rated its own certainty very low on every outcome, because the experiments differed widely and most carried design weaknesses that could tilt a result either way. The older review's ranges were wide enough to hide a real effect: on body weight it ran from a 1.6kg loss to an 11.6kg gain. Not finding an effect is not the same as ruling one out.