Obesity as an influencing factor for the occurrence of caffeine-induced effects in women.

Beckground and aims: Individuals with a higher body fat percentage may have higher serum levels of caffeine and its metabolites and process caffeine more slowly than individuals with a lower body fat percentage, so the aim of this study is to compare the occurrence of positive and negative effects of caffeine in nonobese and obese women.

Methods and results: One hundred and sixty women were included in the study. Body fat was determined using the mBCA 515 SECA analyzer. Participants were divided into 4 groups: nonobese caffeine, nonobese placebo, obese caffeine and obese placebo. Caffeine groups received 6 mg/kg body weight caffeine. Placebo groups received identical starch-filled capsules. One hour after ingestion and within 24 h, participants completed a caffeine-induced effect questionnaire. Caffeine intake showed statistically significant differences compared to placebo for neutral (p ≤ 0.014; Cramér's V = 0.27; 27 % increase), negative (p ≤ 0.002; Cramér's V = 0.34; 34 % increase), and positive effects (p ≤ 0.015; Cramér's V = 0.27; 27 % increase). Further analysis revealed significant associations with increased urine output (p ≤ 0.014; Cramér's V = 0.27; 27 % increase), vigor/activeness (p ≤ 0.009; Cramér's V = 0.29; 29 % increase), and headache (p ≤ 0.033; Cramér's V = 0.24; 24 % increase) 1 h post-ingestion. No significant effects were observed in the placebo group. There was no statistically significant placebo effect.

Conclusions: Obese and nonobese women show different responses to caffeine 60 min after ingesting 6 mg/kg body weight. Obese women are more likely to report adverse effects, including increased urine output, heightened vigor/activeness, and headaches, compared to nonobese women.

Trial registration: ANZCTR12622000823774; June 10, 2022.