Comparison of Popular Weight Loss Diets

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.

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)

Gardner CD, Kiazand A, Alhassan S, Kim S, Stafford RS, Balise RR, Kraemer HC, King AC. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007 Mar 7;297(9):969-77. doi: 10.1001/jama.297.9.969. Erratum In: JAMA. 2007 Jul 11;298(2):178.