The effect of passive and exercise-induced dehydration on body composition using dual energy X-ray absorptiometry

To determine the effect of dehydration on changes in body composition using dual energy x-ray absorptiometry (DXA).

Sixty college students completed a non-exercise control (NEC) and an exercise-induced dehydration (EID) session. Both sessions were held on a climatized control laboratory at 30 °C and a relative humidity of 70 %. Exercise was performed on a stationary bicycle for 60-min at an intensity of 65 %-75 % of the reserve heart rate. Body composition was assessed by DXA before and after the sessions and the mean body composition differences were correlated with the degree of dehydration achieved by the participants.

The experimental sessions elicited dehydration in all the participants (NEC = 0.50 ± 0.51 % vs. EID = 1.11 ± 0.45 %; p ≤ 0.0001; CI95%_diff = -0.75, -0.47 %). In the NEC condition, dehydration (β = 0.51, p ≤ 0.0001) and age (β = 0.22, p = 0.046) predicted the difference in trunk tissue (R² = 0.32). Dehydration (β = 0.93, p ≤ 0.0001) and gender (β = -0.11, p = 0.013) predicted the difference in total tissue (R² = 0.90). Dehydration predicted differences in trunk lean mass (β = 0.37, p = 0.004, R² = 0.14), total lean mass (β = 0.36, p = 0.004, R² = 0.13), and total trunk mass (β = 0.52, p ≤ 0.0001, R² = 0.27). Dehydration (β = 0.95, p ≤ 0.0001) and gender (β = -0.09, p = 0.015) predicted the difference in total mass (R² = 0.94). For the EID condition, dehydration and gender predicted the difference in total tissue (β_dehydration = 0.72, p ≤ 0.0001, β_gender = -0.27, p = 0.001, R² = 0.71) and total mass (β_dehydration = 0.75, p ≤ 0.0001, β_gender = -0.27, p ≤ 0.0001, R² = 0.77). Dehydration (β = 0. 32, p = 0.012) predicted differences in total lean mass (R² = 0.10).

Age, gender and dehydration predicted differences in body composition scores. Technicians and researchers must control hydration status before DXA scan sessions.