Associations among dietary fat oxidation responses to overfeeding and weight gain in obesity-prone and resistant adults

OBJECTIVE: We tested the hypothesis that three days of overfeeding (OF) decreases dietary fat oxidation and predicts longitudinal weight change in adults classified as obesity-prone (OP) and obesity-resistant (OR) based on self-identification, personal and family weight history. Changes in diurnal profiles of plasma metabolites and hormones were measured to probe mechanisms. METHODS: Adults identified as OP (n=22; BMI: 23.9 ± 2.4 kg/m(2)) and OR (n=30; BMI: 20.5 ± 2.2 kg/m(2)) completed 3 days of eucaloric (EU) feeding and 3 days of OF. On day three, 24-hr total and dietary fat oxidation were measured using room calorimetry and an oral (14)C tracer. Plasma glucose, insulin, triglycerides (TG), and non-esterified fatty acid (NEFA) concentrations were frequently sampled over 24-hr. Body composition was measured annually for 4.0 ± 1.4 years in a sub-sample (n=19 OP and 23 OR). RESULTS: Dietary fat oxidation over 24-hr was not altered by OF versus EU (P=0.54). Weight gain in OP correlated with lower nocturnal NEFA concentrations during OF (r=−0.60, P=0.006) and impaired fuel selection over 24-hr (metabolic inflexibility, wake RQ-sleep RQ) (r=−0.48, P=0.04). CONCLUSIONS: Short-term OF did not alter dietary fat oxidation. Lower nocturnal NEFA availability and metabolic inflexibility to overfeeding may be factors contributing to weight gain.