Exploring the individual response to medium-chain triglycerides in long-distance runners using N-of-1 trials

The potential of medium-chain triglyceride (MCT) to enhance athletic performance remains controversial. This study aims to explore how long-term MCT supplementation may enhance endurance and predict individual responders compared to carbohydrates (CHO), while also validating the feasibility of applying the N-of-1 trial design in the field of personalized nutrition. It consists of a series of completed 6-week, single-center, randomized, double-blind, controlled N-of-1 trials, involving a total of 9 long-distance running enthusiasts from Wuhan University (Wuhan, China). The study was divided into 3 cycles, each lasting 2 weeks. During each cycle, participants randomly consumed 400 mL of MCT as the intervention or 400 mL of CHO as the control. The 5-kilometer time trial (5KTT) results were used to assess participants’ endurance, and a Bayesian model was employed to assess individual and aggregated results. Results showed substantial variability in the intervention effect between participants, with improvements in the 5KTT on MCT relative to CHO ranging from –37.54 s (95% credible interval (CrI), –164.25 to 100.35) to 69.37 s (95% CrI, –81.14 to 215.45). The trial observed 1 CHO responder, with a posterior probability of 0.50; 2 MCT responders, with posterior probabilities of 0.57 and 0.64; and 5 non-responders, respectively. The aggregate Bayesian analysis indicated that the posterior probability of achieving a clinically meaningful intervention effect for MCT compared to CHO was only 0.37. Based on these findings, MCT did not improve participants’ running performance compared to CHO at the overall level. However, our study supports that using the N-of-1 trial design can provide more precise personalized recommendations for each participant.