The purpose of the MENU Study is to examine whether there is a differential weight loss response to different dietary macronutrient composition (higher carbohydrate and lower fat versus lower carbohydrate and higher monounsaturated fat [MUFA] or lower carbohydrate and walnut-rich higher fat diets) in a weight loss intervention in healthy obese women, depending on insulin resistance status. Blood samples will be collected to enable analysis of potential mechanisms and differential response across subgroups.

Inclusion Criteria:

• Aged 21 years and older
• Have BMI >30.0 kg/m2 and <40 kg/m2
• Willing and able to participate in clinic visits, group sessions, and telephone and Internet communications at specified intervals
• Able to provide data through questionnaires and by telephone
• Willing to maintain contact with the investigators for 12 months
• Willing to allow blood collections
• No known allergy to tree nuts
• Able to be physically active

Exclusion Criteria:

• Diabetic
• Inability to be moderately physically active
• A history or presence of a comorbid diseases for which diet modification and increased physical activity may be contraindicated
• Currently pregnant/breastfeeding
• Planning to become pregnant within the next year
• Currently enrolled in a weight loss program or diet intervention study
• Current use of weight loss medication or supplements
• Planned surgical procedure that can impact the conduct of the study
• Have plans to relocate from area within the next year
• 6+ months use of meds likely to cause weight gain or prevent weight loss
• Any condition which in the opinion of the investigator makes the subject unsuitable for inclusion in this study