Metabolic flexibility is defined as the ability of the body to switch fuel preferences after some form of stimulation. Metabolic inflexibility is associated with metabolic disorders, including obesity and diabetes. Because obesity has been determined to be the result of an interaction between environmental and genetic factors, it is possible that the influence of parental weight status may influence the child’s metabolic tendencies, even in lean children. PURPOSE: This study examined the effect of parental weight status on the child’s metabolic flexibility, expressed via fat oxidation. METHODS: Subjects were separated into groups based on parental BMI: those with two lean parents (LL, n=5, 10.5±1.3 years old, 31.5±4.6 kg, BMI of 16.9±1.0, 17.9±3.1 % body fat) and those with at least one overweight or obese parent (LO, n=7, 10.2±1.6 years old, 35.6±6.7 kg, 16.9±1.7, 17.6±4.3 % body fat). The experimental visit occurred in the morning, preceded by a standardized breakfast. The child performed two 20-minute exercise bouts, separated by a 10-minute rest. The first bout consisted of 10 minutes at 50% VO2max and 10 minutes at 75% VO2max. The second bout consisted of 20 minutes at 50% VO2max. A two-way (group x time) ANOVA was used to compare the relative contribution of fat (fat use %) and fat oxidation rate (FOX) between the 10-minute time point of the first bout and the 5-, 10-, 15-, and 20-minute time points of the second bout. Significance was set at p≤0.05. RESULTS: There were no significant differences in age, body mass, BMI, or body fat percentage between groups. VO2max was 43.5±6.8 and 44.0±8.1 ml/kg/min in the LL and LO groups, respectively (p>0.05). Fat use % across the five time points ranged from 32.8±20.8 to 48.8±14.9% and from 32.1±7.3 to 40.2±8.4% in the LL and LO groups, respectively. FOX across the five time points ranged from 0.11±0.07 to 0.16±0.06 g/min and from 0.12±0.04 to 0.16±0.05 g/min in the LL and LO groups, respectively. Fat use % and FOX were significantly greater at each time point of the second bout versus the 10-minute time point of the first bout. No significant group or interaction effects were noted. CONCLUSION: This study suggests that parental weight status may not have an effect on the metabolic flexibility in fat metabolism of lean children in the early stages of puberty.