The article hints at this [1], but I haven't researched the issue very deeply. I'd be curious if other HNers know something about this.
[1] "We previously showed [this enzyme] can prevent obesity, diabetes and metabolic syndrome [a disease characterized by a combination of obesity, high blood pressure, a metabolic disorder and insulin resistence]. So, we think that aspartame might not work because, even as it is substituting for sugar, it blocks the beneficial aspects of IAP."