Title: Air displacement plethysmography for estimating body composition changes with weight loss in middle-aged Japanese men Short running head: Body composition change by air displacement method

Aim: To examine the degree to which air displacement plethysmography (ADP) can track body composition changes in response to weight loss in obese Japanese men. Method: Fifty men, aged 30–65 yr, with a mean body mass index of 30 kg/m, received a 3-month weight-loss program. Percentage of fat mass (%FM) was determined by dual energy X-ray absorptiometry (DXA) and ADP at baseline and month 3. Results: With 6.2 ± 4.3 kg of weight loss, %FM, as determined by DXA and ADP, significantly decreased by 3.9 ± 2.9% and 3.9 ± 3.3%, respectively. There was no mean difference for change (Δ) in %FM between the two methods. DXA-derived Δ%FM significantly correlated with Δ%FM determined by ADP (R = 0.48, P < 0.01). Furthermore, the Bland-Altman plots demonstrated no systematic bias for Δ%FM (r = -0.20, P = 0.17). However, %FM by ADP at baseline and Δ%FM by ADP were significantly correlated to the differences between Δ%FM by DXA and ADP (r = 0.42, -0.54, respectively). Conclusion: These results suggest that ADP is comparably accurate for evaluating Δ%FM determined by DXA, although there were proportional biases.