Two-day fasting affects kynurenine pathway with additional modulation of short-term whole-body cooling: a quasi-randomised crossover trial

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

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.

Fasting diets: what are the impacts on eating behaviors, sleep, mood, and well-being?

Fasting diets (FDs) have drawn great attention concerning their contribution to health and disease over the last decade. Despite considerable interest in FDs, the effect of fasting diets on eating behaviors, sleep, and mood-essential components of diet satisfaction and mental health- has not been addressed comprehensively. Understanding the critical role that fasting plays in these elements will open up potential treatment avenues that have not yet been explored. The aim of the present paper was to conduct a comprehensive critical review exploring the effects of fasting on eating behaviors, sleep, and mood. There is currently a lack of clarity regarding which fasting option yields the most advantageous effects, and there is also a scarcity of consistent trials that assess the effects of FDs in a comparable manner. Similarly, the effects and/or treatment options for utilizing FDs to modify eating and sleep behaviors and enhance mood are still poorly understood. Further researches aiming at understanding the impacts of various fasting regimes, providing new insights into the gut-brain axis and offering new treatment avenues for those with resistant anxiety and depression, are warranted. Alteration of eating behaviors can have lasting effects on various physiological parameters. The use of fasting cures can underpin ancient knowledge with scientific evidence to form a new approach to the prevention and treatment of problems associated with co-morbidities or challenges pertaining to eating behaviors. Therefore, a thorough examination of the various fasting regimens and how they impact disease patterns is also warranted.

Stability Studies of Kynurenine Pathway Metabolites in Blood Components Define Optimal Blood Processing Conditions

The kynurenine pathway (KP) is the main pathway of tryptophan (TRP) metabolism that generates energy for multiple cellular processes. The activity of this pathway has been shown to be dysregulated in multiple human diseases. The resultant modulation of metabolites has been suggested to comprise biomarkers to track disease progression or could identify new therapeutic targets. While metabolite changes can be measured readily in blood, there is limited knowledge on the effect of blood matrices and sample processing time may have on the stability of KP metabolites. Understanding the stability of KP metabolites in blood is integral to obtaining accurate KP data to correlate with clinical pathology. Hence, the aim of this study was to assess the concentration of KP metabolites in matched whole blood, plasma and serum. The impact of pre-analytical sample processing time in the various blood matrices was also analysed. Serum and plasma had the higher concentration of KP metabolites compared to whole blood. Furthermore, concentrations of KP metabolites declined when the collected blood was processed after 24 hours storage at 4°C. Our study shows that that type of blood matrix and the time to processing have an impact on the stability of the KP metabolites. Serum or plasma are the preferred choice of matrix and the isolation of these matrices from whole blood is best performed immediately after collection for optimal analytical KP data.

Short-duration cold exposure decreases fasting-induced glucose intolerance but has no effect on resting energy expenditure

The aim of the present study was to investigate whether brief cold exposure can reverse fasting-induced glucose intolerance and insulin resistance, and improve resting energy expenditure (REE). Twelve young non-obese women were randomly assigned to undergo the following conditions: 2 days of fasting with two 10-min whole-body cold-water immersions on separate days (FAST-COLD), 2 days of fasting without cold-water immersions (FAST), 2 days of usual diet with two 10-min whole-body cold-water immersions on separate days (COLD), or 2 days of usual diet without cold-water immersions (CON) in a randomised crossover fashion. Changes in REE and substrate utilisation, and glucose tolerance and insulin sensitivity from the oral glucose tolerance test were examined. The results showed that FAST-COLD and FAST trials increased (P < 0.05) REE and decreased (P < 0.05) respiratory quotient, but these variables did not differ significantly between the FAST-COLD and FAST trials. The glucose and insulin area under the curves (AUCs) were higher (P < 0.05) in the FAST-COLD and FAST trials than in the CON and COLD trials, and these AUCs were lower (P < 0.05) in the FAST-COLD than in the FAST trial. Matsuda index was lower in the FAST trial than in the CON trial (P < 0.05), and tended to be greater after the FAST-COLD trial than after the FAST trial (P = 0.060). In conclusion, cold exposure had no effect on REE but decreased fasting-induced glucose intolerance which was accompanied by a maintained insulin sensitivity.