The principal objective of the DPP is to prevent or delay the development of NIDDM in those persons who are at high risk for its development by virtue of having impaired glucose tolerance. Impaired glucose tolerance represents a less severe stage of blood glucose abnormalities that often precedes NIDDDM. The primary outcome is the development of diabetes according to American Diabetes Association criteria (fasting plasma glucose level > 126 mg/dL [7.0 mmol/L] or 2-hour plasma glucose > 200 mg/dL [11.1 mmol/L]), after a 75 gram OGTT, and confirmed with a repeat test). Secondary outcomes will focus on cardiovascular disease and its risk factors and changes in glycemia, insulin secretion and sensitivity, obesity, physical activity and nutrient intake, and the occurrence of adverse events. For the primary outcome time to development of diabetes, product-limit life-table distributions of each intervention group and the control group will be compared using the log-rank test statistic. The primary analyses will include all participants in their randomly assigned treatment group, regardless of adherence to the assigned treatment (intention-to-treat principle).