Objective: The objective of this study was to evaluate the effectiveness of an Internet-based 12-Week Healthyfor Life Program in supporting weight loss and improvements in metabolic and cardiovascular health among subjects with metabolic syndrome. Research methods and procedures: Sixty subjects with metabolic syndrome were studied before, during, and after a 12-week online lifestyle intervention program that prescribed a low-glycemic diet, nutritional supplementation, and moderate exercise. Results: The intervention produced an average weight loss of 5.5 kg (5.4%). Measures of glycemic control improved significantly during the study. Fasting insulin was reduced by 32.3% and 120-minute insulin during an oral glucose tolerance test was reduced by 43.6%. Insulin sensitivity was increased as evidenced by a reduction in the homeostatic model assessment (HOMA) index (by 31.6%) and an increase in the insulin sensitivity index. There were also significant improvements in triglycerides, total cholesterol, and blood pressure. At the end of the study, 58.5% of the study completers met criteria for the metabolic syndrome compared to 84.9% at baseline (p = 0.002). Summary : This study demonstrates than an online lifestyle change program that prescribes a low-glycemic diet, nutritional supplements, and moderate exercise can successfully produce meaningful weight loss, significant improvements in glycemic control, and significant reductions in risk factors for heart disease in individuals with metabolic syndrome. Copyright 2009, Mary Ann Liebert, Inc.