Moderate coffee intake does not significantly affect short-term bioelectrical impedance measurements in healthy women

Bioelectrical impedance analysis (BIA) is a widely used, noninvasive method for assessing body composition. However, its sensitivity to acute changes in water consumption and coffee intake raises concerns about measurement reliability. This study hypothesized that the short-term consumption of 200 mL caffeinated or decaffeinated coffee would result in measurable changes in BIA-derived body composition parameters compared to water intake. Twenty-seven healthy female participants (aged 18-35 years; body mass index 18.5-29.9 kg/m²) were randomly assigned to one of three groups: caffeinated coffee, decaffeinated coffee, or water (n = 9 per group). After all groups consumed 200 mL of the assigned beverage, BIA measurements were performed at baseline, 30, 60, 90, and 120 minutes using the InBody 270 analyzer. Nonparametric tests (Kruskal-Wallis, Friedman) and Quade ANCOVA were applied to assess between- and within-group differences, adjusting for baseline values. Significant within-group changes were observed in body weight and body mass index across all groups (P < .05). Between-group differences emerged in fat mass, fat percentage, and body mass index at multiple time points (P < .05); however, none remained significant after adjusting for baseline using Quade ANCOVA (all P > .05). Notably, several parameters showed medium to large effect sizes, despite nonsignificant P values. Under controlled conditions, moderate caffeine intake (∼95 to 100 mg) or 200 mL fluid volume does not induce significant short-term alterations in BIA-derived body composition in healthy women. Visual trends suggest transient fluctuations within the first 60 minutes, though these were not clinically meaningful.