2.3. Procedure
COLD
The experimental procedure comprised two separate testing visits (visit 2: baseline; visit 3: post-intervention) performed at baseline and after 6 weeks starting at 1:00 p.m. following a 24 h abstention from alcohol, coffee (caffeinated or decaffeinated), other caffeinated products, or any other stimulant. Prior to the test visits, participants collected a fecal sample at home and awakening saliva samples as previously described [Subsequently, participants performed the Maastricht Acute Stress Test (MAST) according to procedure described in Smeets et al. (2012). In brief, the MAST consisted in a first 5 min period of instruction (stress anticipation), followed by a 10 min period of physical (hand immersion in cold water), with cognitive (mental arithmetic trials) and social (videotaping) stressors alternately administered by a trained experimenter [