Waistlines in people, glucose levels in mice hint at sweeteners' effects: Related studies point to the illusion of the artificial

"Diet" soft drink consumption is associated with increased waist circumference in humans, and aspartame raised fasting glucose (blood sugar) in diabetes-prone mice.

The toxic effects of aspartame have been known for decades following John Olney's pioneering work with excitotoxins in 1969:
In 1981, this paper , by Takasaki et al showed that feeding aspartame to thirsty young  mice produced ledions in the arcuate nucleus, the hypothalamic region that controls appetite.

Other work has also linked aspartame to weight gain Yang 2010 and others