A myriad of diabetes prevention programs are carried out worldwide to fight against the current type 2 diabetes (T2D) pandemic. The lack of a unified criterion for evaluating the efficacy of T2D prevention programs, however, makes the interpretation of prevention program results difficult, and hinders clear and direct comparisons of different prevention programs. Metabolic syndrome is a strong indicator for diabetes and its complications, holding great promise to become the basis of an intervention evaluation method. The Metabolic Syndrome Index (MSI), proposed here, quantifies the metabolic risk for developing T2D and its complications. The MSI is a novel scale for evaluating the efficacy of diabetes prevention programs because it is a systematic, comprehensive, and stable indicator that reflects the metabolic risk reduction for diabetes and its complications at multiple levels and dimensions.