In obesity, a situation is created in which energy intake exceeds energy expenditure. The three components of energy expenditure are resting metabolism, physical activity, and thermogenesis. Increasing attention is being paid to the role of impaired energy expenditure in obesity. Evidence indicates that impairment in activity of the sympathetic nervous system, which stimulates thermogenic processes, contributes to the etiology of obesity. In addition, insulin resistance, a well-recognized metabolic consequence of obesity, appears to interfere with feeding-related, insulin-mediated increases in thermogenesis in brown adipose tissue. This thermogenic defect results in reduced energy buffering by brown adipose tissue leading to deficient energy expenditure and an increased efficiency in weight gain. A unique weight loss program, The Princeton Metabolic Diet Program, is presented. The Program stimulates metabolism by stimulating the sympathetic nervous system and correcting insulin resistance, thereby enhancing thermogenesis in brown adipose tissue. Methods include: 1) alternating diet composition and caloric intake and, 2) the use of nutritional metabolic stimulants. This type of non-toxic therapy, directed at correcting biochemical defects, will enhance metabolic mechanisms and induce weight loss.