The [1-¹³C]acetate recovery factor to correct tracer-derived dietary fat oxidation is lower in overweight insulin-resistant subjects

Background&aims: An acetate recovery factor (ARF) is utilized to correct tracer-derived fat oxidation when ¹³C is used. We showed that when ¹³C labelled fatty acid are given orally, dietary fat oxidation can be accurately corrected by using an averaged dietary ARF (dARF) derived from 56 lean healthy subjects, instead of individual dARF. The extent to which this factor is valid in overweight insulin resistant subjects is unknown. Methods: [1-¹³C]dARF and [1-¹³C]fatty acid recoveries were assessed before and after physical activity/inactivity interventions in overweight insulin-resistant (n = 11) and lean subjects (n = 70) in five studies herein compiled. Results: Overweight dARF was lower compared to lean subjects (45.3 ± 1.5% vs. 50.6 ± 0.6%; P = 0.002). Physical activity intervention did not impact dARF. dARF correlated negatively with %body fat (r² = 0.10; P = 0.005) and fasting insulin to glucose ratio (r² = 0.08; P = 0.02). Applying the lean average [1-¹³C]dARF induced an 11.5% (P = 0.006) average error in fatty acid oxidation rate. Conclusions: Overweight insulin resistant subjects have lower dARF than lean individuals. An average dARF derived from lean subjects cannot be applied in overweight subjects to calculate dietary fat oxidation. We recommend that individual dARF are measured in subjects with metabolic disorders.