• Weight; measured at each study visit
• Percent body fat; measured at each study visit

• Weight
• Percent body fat

• Blood lipids (cholesterol, triglycerides); measured at each study visit
• Fasting insulin and glucose; measured at each study visit
• Behavioral variables; measured at each study visit

• Blood lipids (cholesterol, triglycerides)
• Fasting insulin and glucose
• Behavioral variables

This study will compare the safety and effectiveness of three popular weight loss plans. These plans will be compared with the USDA Dietary Guidelines.

Obesity is the single most significant, nutrition-related health issue of the new millennium. Several “medical experts” have designed and promoted weight loss diets that dramatically differ from one another and from the USDA Dietary Guidelines. These diets have gained surprisingly widespread and persistent popularity among Americans despite the lack of evidence supporting their claims. This clinical trial will provide preliminary feasibility data for a full-scale study that will examine health outcomes (e.g., benefits, risks, success) of three popular weight loss diets. The study will investigate behavioral and physiological factors that influence adherence and retention to these diet plans.

Overweight women will be randomly assigned to one of four diets for 1 year: Atkins (extremely low carbohydrate), Zone (low carbohydrate, high protein), Ornish (very low fat), or USDA/Food Pyramid (high carbohydrate/moderate-low fat). Behavioral and physiological data will be collected. Participants attend study visits at baseline, 8 weeks, 6 months, and 1 year. At these visits, measurements will include that will include weight and blood pressure measurements and blood tests. Participants will be asked to complete ten questionnaires over the course of the study to assess behavior and appetite. Participants will also undergo a DEXA scan to assess body composition.

• Behavioral: Atkins diet (extremely low carbohydrate)
• Behavioral: Zone diet (low carbohydrate, high protein)
• Behavioral: Ornish diet (very low fat)

Inclusion Criteria

• Body mass index (BMI) between 27 and 40 kg/m2
• Weight stable for last 2 months
• Not actively on a weight loss plan
• No plans to move from the area over the next 2 years
• Willing to accept random assignment

Exclusion Criteria

• Pregnant or breastfeeding
• Within 6 months of giving birth or planning to become pregnant in the next 2 years
• Diabetes (type 1 or 2) or history of gestational diabetes
• Renal or liver disease, active neoplasms, or recent myocardial infarction
• Hyper- or hypothyroidism
• Lipid lowering medications or medications known to affect weight/energy expenditure
• Excessive alcohol intake (self-reported, > 3 drinks/day)
• Postmenopausal, including surgical menopause
• Currently under psychiatric care or severely clinically depressed (> 17 on Beck Inventory)