Artificial sweeteners may be nonnutritive, but they can still affect metabolism. At the Experimental Biology meeting held last week in San Diego, Brian R. Hoffmann, a biochemist at the Medical College of Wisconsin, reported that acesulfame potassium changes the metabolome of rats whose normal diet is supplemented with the artificial sweetener, which is widely used in diet soft drinks. Rats received plain water or water sweetened with glucose, acesulfame, or aspartame, another artificial sweetener. After three weeks, Hoffmann and his team took a broad look at metabolites in the rats’ blood plasma using high-throughput mass spectrometry. Then Hoffmann’s team compared the diversity of metabolomes resulting from each sweetener. Acesulfame led to more distinct changes in the rats’ metabolomes than did the other sweeteners. By the end of the three-week study, acesulfame had accumulated in the rats’ blood, which suggests it overwhelmed the animals’ ability to clear it following chronic consumption. Hoffmann plans to perform longer studies and to include a wider variety of artificial sweeteners to further understand the implications of the metabolome alterations.