The AACC International Board of Directors appointed an ad hoc Glycemic (Net) Carbohydrate Definition Committee in September 2004, which, after much discussion, recommended definitions for “available carbohydrate,” “glycemic response,” “glycemic carbohydrate,” and “glycemic impact.” The committee also developed a definition for “glycemic impact” to quantify the expected relative effect that a food would have on postprandial glycemic response. Currently, the only measurement is by an in vivo method. The committee recommended that an effort be made to develop validated in vitro methodology that accurately mimics in vivo behavior.