This study will compare the safety and effectiveness of a low carbohydrate diet (Atkins Diet) with a high carbohydrate diet (conventional USDA diet).

Despite the considerable mass appeal of popular diet books, such diet approaches lack data to support their efficacy and safety. Despite its widespread use for more than 30 years, the Atkins diet has never been evaluated in a large, randomized, controlled trial. This study will assess the short-term and long-term clinical effects of a low-carbohydrate diet and a high-carbohydrate diet in overweight and obese men and women.

Participants in this study will be randomly assigned to the Atkins diet (low-carbohydrate, unlimited fat and protein) or a conventional USDA diet (high-carbohydrate, low fat). The study will evaluate the effects of each dietary approach on changes in: 1) weight and body composition, 2) metabolic and organ function, 3) exercise tolerance. Each participant will be enrolled in the study for 2 years.

Inclusion Criteria:

• Body mass index between 30 and 40
• Live and work within 1 hour of the study site
• Stable psychological status

Exclusion Criteria:

• History of heart disease, heart attack, or stroke
• Blood pressure > 140/90 mmHG
• Abnormal cholesterol levels
• Significant psychiatric illness
• Any medication that affects weight or metabolic rate
• Presence or history of a chronic disease that is known to affect appettite, food intake, or metabolism (i.e. diabetes, thyroid disease or cancer).
• Currently using antidepressants, steroids, tobacco or illegal drugs
• Pregnant, breastfeeding, or planning pregnancy
• 10 lb change in weight within 6 months of study entry
• History of malignant arrhythmias or cerebrovascular, renal, or hepatic disease
• History of protein wasting diseases or gout
• Severe arthritis
• Osteoperosis
• Certain types of hormone replacement therapy
• Currently following a vegetarian diet