Examining the Effects of Diet on Health in Prediabetes With an Online Program

* Inclusion criteria 1. Self-reported clinical diagnosis of prediabetes occurring within the past year. 2. Aged 18 years old and older 3. Per the Centers for Disease Control and Prevention Diabetes Prevention Recognition Program have a self-reported body mass index (BMI) of ≥ 24 kg/m2 (≥ 22 kg/m2 if Asian). 4. Willing and able to participate in the intervention such as having sufficient control over their food intake. Must have the ability to make choices about the food they eat; cannot have a lifestyle in which they eat out most of their meals.) * Exclusion criteria 1. Unable to provide informed consent. 2. Non English speaker. The intervention groups are conducted in English. 3. No current use of insulin, no immediate plans to start or increase diabetic mediations, and no use of diabetes medications besides metformin. Insulin and other diabetes medications other than metformin can alter the safety of the diets, so to ensure greater safety, we will exclude diabetics using insulin or medications besides metformin. 4. A substance abuse, mental health, or medical condition that, in the opinion of investigators, will make it difficult for the potential participant to participate in the intervention. Such conditions may include: cancer, liver failure, unstable coronary artery disease, severe emphysema, binge eating disorder or history of binge eating disorder, bulimia or strong history of bulimia. 5. Previous use or recent changes in medications that can interfere with the measures used in the study: current use of insulin; use of systemic (oral or IV) corticosteroids in the 1 month prior to enrollment or severe autoimmune disorders or other conditions (e.g. rheumatoid arthritis, lupus), that are likely to require these medications; and initiation of new class of psychiatric medications in past 2 months. Such medications can alter measures used in our research, such as assessments of markers of inflammation, or negatively influence the safety of the diets. 6. Pregnant or planning to get pregnant in the next 12 months, breastfeeding or less than 6 months post-partum. The intervention is not designed for the particular diet considerations during pregnancy and breast-feeding. 7. Current use of weight loss medications or supplements such as Alli or amphetamine-based drugs that are believed to have some effect on weight. Use of weight loss aids by potential participants will be reviewed by a core study team to determine whether participant would be eligible if they stop using the substance. 8. History of or planned weight loss surgery. The intervention is not designed to address either the often substantial food intake limits that often result from weight loss surgery or the significantly disordered eating that people who fail this extreme intervention may have. 9. Vegan or vegetarian. The intervention diets are more challenging for vegan and vegetarian participants. 10. No or very limited internet access at a computer. Must be able to complete the online assessments and access the online class materials.