Associations of Anthropometry and Handgrip Strength with Bioelectrical Impedance Parameters in Irritable Bowel Syndrome: A Cross-Sectional Study

Background/Objectives: Simple anthropometry may complement nutritional assessment in irritable bowel syndrome (IBS). We examined the associations of arm anthropometry and handgrip strength (HGS) with bioelectrical impedance analysis (BIA) parameters. Methods: This cross-sectional baseline analysis included 55 adults with IBS-D or IBS-M for valid non-adiposity measurements; 54 contributed valid paired body-fat estimates, and 54 had valid dominant-hand HGS. Results: MUAMC correlated with BIA-derived skeletal muscle mass within men (Spearman’s ρ = 0.748) and women (ρ = 0.673). After adjustment for sex, age, height and body weight, the MUAMC association was attenuated (β = 0.0337 kg/mm, 95% CI 0.0059–0.0616; p = 0.0187). MUAMC was correlated with phase angle in the pooled sample (ρ = 0.806), but sex-related differences were exploratory. In a sensitivity model using the impedance index, the association was not significant after further adjustment for body weight (β = 0.0670, 95% CI −0.0087 to 0.1427; p = 0.0816). HGS correlated with BIA-derived skeletal muscle mass before adjustment (ρ = 0.769; n = 54), whereas an adjusted association was not established. BIA- and skinfold-derived body-fat estimates were correlated but showed proportional bias, limiting interchangeability. Conclusions: MUAMC is associated with BIA-derived muscle-related parameters, but mathematical coupling, body size and the absence of a criterion method limit causal and validation claims. Findings from this exploratory single-centre analysis require independent confirmation.