GoKawiilEthical approval
This protocol is a basic experimental study involving humans since it is a systematic study directed toward greater understanding on how coffee intake in healthy individuals influences the microbiome and behaviour with no intention to change the health status of the participants.
The study protocol was approved by the Clinical Research Ethic Committee of the Cork Teaching Hospitals (Study Identification Number APC115) and was registered in the Clinical Trials portal with the ClinicalTrials.gov ID NCT05927038, “Coffee Consumption, the Gut Microbiome, and the Microbiota-Gut-Brain Axis” and NCT05927103 “Differences Between Coffee and Non-coffee Drinkers in the Gut Microbiome and Microbiota-Gut-Brain Axis”. Informed consent was obtained from every participant enrolled in the study.
Study design
Sixty-two healthy adults between 30 and 50 years of age living in Ireland were recruited for the study between September 2021 and January 2023. Thirty-one participants were non-coffee drinkers (NCD, i.e., people that never consume coffee) and thirty-one participants were moderate coffee-drinkers (CD, i.e., people that usually consume between 3 to 5 cups of coffee per day). NCD and CD participants were compared cross-sectionally at baseline. CD participants only proceeded further with the study and were asked to abstain from any kind of coffee for 2 weeks. After the coffee washout period, CDs were block randomized (block of five, stratified by gender) into either caffeinated or decaffeinated coffee consumption group using a double-blinded, parallel design by the first author. Figure S17 details information relative to participants enrolment and allocation.
Study visits and coffee intervention
A scheme of the experimental design is displayed in Fig. 1A. During the screening visit at University College Cork the eligibility of the participants was verified. Demographics, medical and family history information were collected. MINI-international Neuropsychiatric Interview (M.I.N.I, version 7.0.2), Childhood Trauma Questionnaire (CTQ) and Rome IV Diagnostic Questionnaire for Functional Gastrointestinal Disorders in Adults (ROME-IV) were administered to assess the overall mental and gastrointestinal health of the participants63,64. Habitual caffeine consumption was assessed by a 7-day caffeine consumption diary and a brief measure of verbal IQ was completed using National Adult Reading Test (NART)65 (Supplementary Data 1). Both NCD and CD participants were asked to abstain from any other kind of caffeinated drink and dark chocolate during the week before the baseline visit, except their habitual coffee for CDs only.
During the baseline visit, the participants underwent a brief physical examination, and their samples were collected. Subsequently, the participants completed self-reported mood and behaviour questionnaires (see below), cognitive tasks and the Socially Evaluated Cold Pressor Test (SECPT). At the end of the baseline visit, NCDs participant concluded the study and received thirty euros compensation for any travel expenses incurred in taking part in the study. CDs participants were instructed to refrain from any caffeinated drink, any kind of coffee or dark chocolate for 2 weeks. After coffee/caffeine washout, CDs attended the pre-intervention visit in which they underwent a physical examination, samples collection and completed self-reported questionnaires as well as Paced Auditory Serial Additional Test (PASAT) cognitive test. During this visit, CDs were instructed to drink four sachets per day of the provided coffee (Nescafé Classic caffeinated or decaffeinated, 1.8 g instant coffee per sachet) for 3 weeks, beginning on that day.
No other coffee or caffeinated drinks were allowed during the intervention. The coffee provided was consumed with a quantity of hot water, milk, sugar chosen by the participant. CDs completed the study with the post-intervention visit (Visit 4), in which they completed the same measures as for V2 and received sixty euros compensation. Extra stool samples from CDs were collected 2 (day 2) and 4 (day 4) days after the start of coffee withdrawal and 2 (day 16), 4 (day 18) and 14 (day 28) days after the start of coffee intervention. Together with the samples, CDs completed mood, fatigue, and cravings questionnaires.
Exclusion criteria
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