Associations Among Dietary Fat Oxidation Responses to Overfeeding and Weight Gain in Obesity-Prone and Resistant Adults

Objective: This study tested the hypothesis that 3 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 and 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/m² ) and OR (n = 30; BMI: 20.5 ± 2.2 kg/m² ) completed 3 days of eucaloric (EU) feeding and 3 days of OF. On day 3, the 24-hour total and dietary fat oxidation was measured using room calorimetry and an oral ¹⁴ C tracer. Plasma glucose, insulin, triglycerides, and nonesterified fatty acid (NEFA) concentrations were frequently sampled over 24 hours. Body composition was measured annually for 4.0 ± 1.4 years in a subsample (n = 19 OP and 23 OR).

Results: Dietary fat oxidation over 24 hours 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 hours (metabolic inflexibility, wake respiratory quotient-sleep respiratory quotient) (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.