Unsaturated fatty acids enhance metabolic flexibility by accelerating time-based RQ dynamics

The quality of dietary fatty acids may influence metabolic flexibility and metabolic health.

To determine whether dietary fatty acid quality, independent of total fat content, differentially affects postprandial metabolic flexibility assessed using time-based respiratory quotient (RQ) dynamics and acylcarnitine profiles.

Fourteen healthy young men completed three randomized, single-blind crossover trials with isoenergetic high-fat meals enriched in palmitic acid (PA), oleic acid (OA), or α-linolenic acid (ALA), each providing 45% of total energy from fat. Whole-body energy metabolism was assessed using indirect calorimetry over 13 hours, and blood and urine samples were collected for acylcarnitine analysis.

Time to peak RQ was shorter in the OA trial than in the PA trial (68 ± 53 vs. 166 ± 101 min; P = 0.023). Time to food quotient (FQ) was shorter in both the OA and ALA trials than in the PA trial (239 ± 40 and 237 ± 86 vs. 271 ± 27 min; P = 0.030 and 0.007, respectively). The serum C2-acylcarnitine-to-free carnitine ratio was higher in the OA trial than in the PA trial in both postprandial (P = 0.004) and next-morning fasting states (P = 0.009). Urinary C2-acylcarnitine concentrations were higher in the OA (P = 0.006) and ALA (P = 0.041) trials than in the PA trial. Serum and urinary acylcarnitine indices were significantly associated with time to FQ but not with time to peak RQ.

Despite being isoenergetic and containing the same proportion of energy from fat, meals enriched in unsaturated fatty acids promoted faster time-based RQ dynamics and more efficient postprandial substrate switching than PA-rich meals, accompanied by distinct acylcarnitine responses. These findings suggest that dietary fatty acid quality influences metabolic flexibility and support the integration of time-based RQ dynamics and acylcarnitine profiling to characterize its functional and metabolic components.

This trial was registered at https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000057763 as UMIN000050707.