Influence of physical activity on hydration state in children with obesity before and after a weight loss program.

Objective: Evaluate the effect of a 1-year standardized residential slimming program on exercise-induced dehydration in children with obesity. Method: At the start (T1) and end (T2) of the program, urine samples, weight, blood pressure and pulse were collected before (TR) and after a Cooper test (TE). Urinary samples were analyzed for volume, Na (UNa), Cl, K (UK), urea, creatinine (Ucreat), protein and osmolality (Uosm). Results: All 66 children (15 ± 1 years) starting the program were included after informed consent (28 stopped prematurely). The Cooper test induced a significant weight loss at each test moment (p < 0.01). The resting UK/(UNa + UK) % increased significantly from 40 (±11) at T1 to 50% (±11) at T2. Only in normal weight patients, exercise induced a significant increase in UK/(UNa + UK) % (T2R: 49 ± 11; T2E: 56 ± 12) (p < 0.01) as well as an increase in UNa/Ucreat mmol/mg (T2R: 0.12 ± 0.07; T2E: 0.1 ± 0.05) (p < 0.05). Conclusion: The significant weight loss after exercise indicated significant dehydration. In patients with obesity, no aldosterone effect measured by UK/(UNa + UK)% was observed in contrast to the normal body mass index patients after the program.