The objective of this study was to assess the effects of weight history status and ethnicity on the ability of the Harris-Benedict (HB) formula to (1) predict measured resting energy expenditure (REE) and (2) accurately estimate energy needs over a 2-week test period. Subjects were never-overweight (body mass index [BMI] ≤25 kg/m2, n = 47), overweight (BMI 27-30 kg/m2, n = 170), and weight-reduced (BMI ≤25 kg/m2, n = 51) healthy, adult African American and white women. Food was provided for 2 weeks at an energy level calculated using the HB formula multiplied by a 1.35 activity factor. After 2 weeks, weight, REE (by indirect calorimetry), and body composition (by dual-energy x-ray absorptiometry) were assessed. Data were analyzed using 2-way analysis of variance at P < .05 significance. The HB formula overestimated REE (1) in each weight history group (by 669 ± 523 kJ among never overweight, 1234 ± 791 kJ among overweight, and 439 ± 565 kJ among weight reduced) such that there was a group effect on overestimation (P < .001) and (2) between ethnicities, with a greater overestimation in African American versus white subjects (P < .001). There was a significant effect of weight history group on weight change (P < .001) over 2 weeks, such that weight-reduced women gained more weight than the other 2 groups (P < .05). In conclusion, the ability of the HB formula to estimate REE differed with weight history status and ethnicity. The accuracy of the HB formula to predict dietary energy needs was affected by weight history status. These results suggest that formulas used to calculate energy needs should take into account weight history and ethnicity. © 2007 Elsevier Inc. All rights reserved.