Now, researchers from the Massachusetts General Hospital (MGH) have found a lead. "We found that aspartame blocks a gut enzyme called intestinal alkaline phosphatase (IAP)". IAP is produced in the small intestine. "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."
The researchers confirmed their suspicions via a variety of tests on mice. In one case, they fed IAP directly to mice, who were also on a high-fat diet. It turned out that the IAP could effectively prevent the emergence of the metabolic syndrome. It also helped relieve symptoms in animals that were already suffering from the obesity-related illness.