Exploring the effect of prolonged fasting on kynurenine pathway metabolites and stress markers in healthy male individuals

Abstract

Background/objectives: Prolonged fasting triggers a stress response within the human body. Our objective was to investigate the impact of prolonged fasting, in conjunction with stress, on kynurenine pathway metabolites.

Subjects/methods: Healthy males were divided into fasting group (zero-calorie-restriction) for 6 days (FAST, n = 14), and control group (CON, n = 10). Blood and saliva samples were collected at baseline, Day 2, Day 4, Day 6 during fasting period, and 1 week after resuming regular diet. Plasma levels of kynurenine pathway metabolites were measured using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Plasma and salivary samples were analyzed for stress markers.

Results: A pronounced activation of the kynurenine pathway in individuals on FAST trial was revealed. Concentrations of picolinic acid (PIC), kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK) were significantly increased, with peak levels observed on Day 6 (P < 0.0001). Conversely, concentrations of tryptophan (TRP) and quinolinic acid (QUIN) decreased (P < 0.0001), while kynurenine (KYN) and nicotinamide (NAM) levels remained stable. Cortisol and noradrenaline concentrations remained unchanged. However, adrenaline levels significantly increased on Day 4 within FAST compared to CON (P = 0.005). Notably, all deviations in kynurenine pathway metabolite levels returned to baseline values upon resuming regular diet following the 6-day fasting regimen, even when weight and BMI parameters were not restored.

Conclusions: Extended fasting over 6 days induces the kynurenine pathway and has minimal effects on stress markers. Restoration of metabolite concentrations upon regular feeding implies rapid adaptation of the kynurenine pathway synthetic enzymes to maintain homeostasis when faced with perturbations.

Fig. 1. Schematic representation of the experimental protocol for the FAST trial and CON trial.

Blood and saliva samples taken at baseline, Day 2, Day 4, Day 6 and Day 13. FAST; fasting (0 kcal/day), CON; usual diet. Created with BioRender.com.

Fig. 2. Weight data for FAST and CON groups.

Weight was recorded every day during fasting and subsequently 1 week of recovery. Data are shown in mean ± SEM. ****P < 0.0001, compared with FAST group baseline values, ⁺⁺⁺⁺P < 0.0001, for Day 6 -Recovery comparisons within FAST group. FAST; fasting (0 kcal/day), CON usual diet.

Fig. 3. Effects of FAST and CON on kynurenine pathway metabolite concentrations.

Data are shown in mean ± SEM. *P < 0.05, **P < 0.01, ****P < 0.0001, compared with FAST baseline values. ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, ^####P < 0.0001 for between group comparisons, ⁺⁺P < 0.01, ⁺⁺⁺⁺P < 0.0001, for Day 6 - Recovery comparisons within FAST group. FAST; fasting (0 kcal/day), CON usual diet.

Fig. 4. Effects of FAST and CON on stress marker concentrations: salivary and plasma cortisol, noradrenaline, and adrenaline.

Data are shown in mean ± SEM. **P < 0.01, compared with FAST baseline values. FAST fasting (0 kcal/day), CON usual diet.