The purpose of this study was to investigate whether the genetic polymorphisms of the uncoupling protein 1 (UCP1) and beta 3 adrenergic receptor (beta3-AR) were associated with differences in weight loss and lipid profiles in obese premenopausal women exposed to low-calorie meal replacements over a period of six weeks. Forty women between the ages of 20 and 35 were randomly divided into two groups, each of which consumed one of two low-calorie meal replacements containing either white rice or mixed rice. Although body weight, body mass index (BMI), blood glucose concentration, triglycerides, total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C) were not significantly different by the UCP1 genotype in the white rice group, there were significant differences in body weight (p = 0.041), BMI (p = 0.027), and blood glucose concentration (p = 0.047) between carriers and non-carriers of the G allele in the mixed rice group after the six-week meal replacement intervention. The beta3-AR polymorphism showed no apparent affect on these parameters. Dietary fiber affects weight gain since it is closely related with absorption of nutrients. As a result, the AA type UCP1 genotype produced significant weight loss in the mixed rice group, but not in the white rice group.