Disclosure of Genotype Information to Reduce Caffeine Intake in Slow Metabolizers: Findings from a Randomized Controlled Trial on Personalized Dietary Interventions

<b>Background/Objectives:</b> This study evaluated whether personalized nutrition (PN) advice combined with disclosure of genetic information leads to a greater reduction in caffeine consumption than PN advice alone in slow caffeine metabolizers in the short and long terms. Additionally, Ecological Momentary Assessment (EMA) was considered for its potential to improve dietary intake assessment. <b>Methods</b>: In 2019-2021, 94 adults (aged 18-60 years, C allele carriers of rs762551 <i>CYP1A2</i>, consuming ≥ 200 mg/day caffeine), 63% of whom were women, participated in a twenty-week intervention. Participants were randomized to receive PN with genotype information (the intervention group, n = 55) or without it (the control group, n = 39). All participants were advised to limit caffeine intake to 100 mg/day. Caffeine intake was assessed using a food frequency questionnaire and a smartphones application. After three years caffeine intake was reassessed. <b>Results</b>: After the intervention, caffeine consumption decreased (intervention group: 380.69 ± 217.58 to 153.73 ± 98.19 mg/day; control group: 394.44 ± 256.29 to 169.87 ± 85.70 mg/day; <i>p</i> < 0.01), with no group differences (<i>p</i> = 0.41). Three years later, a reduction (<i>p</i> < 0.01) was still observed in the intervention group, but the effect of time x group was insignificant. In total, 63% of the intervention group and 51% of the control group responded to at least three EMA prompts per day for at least three days. <b>Conclusions</b>: PN seems to affect caffeine intake in the long term. However, including genotype information in PN is no more effective than receiving PN recommendations without genetic information. EMA's effectiveness in large-scale nutritional research may be limited due to the relatively low response rate.