Body fluid retention and body weight change in anorexia nervosa patients during refeeding.

Background & Aims: Body weight gain is an important goal in anorexia nervosa (AN) patients, but inflation in body fluids could artificially increase body weight during refeeding.

Methods: 42 malnourished adult AN patients were refed using a normal-sodium diet, then 176 other malnourished adult AN patients received a refeeding low-sodium diet (BMI of the 218 patients: 13.4 ± 1.9 kg/m(2)). Sodium balance, body composition by a 2-electrode impedance method (BIA, for assessment of total and extracellular water, fat-free mass, FFM), resting energy expenditure and energy intake were calculated.

Results: In the patients on normal-sodium diet, body weight, and total and extracellular water gains were higher than those of the low-sodium diet patients (P<0.01). Edema occurred more often in the former group (21% vs 6%; P<0.05). In almost all patients, BMI reached a plateau around 15-16 kg/m(2), then increased again. During this plateau, an increase in intracellular water and in "active FFM" was observed with BIA, together with a similar decrease in extracellular water.

Conclusion: In AN patients, who are always afraid of gaining too much weight, in regard to their food intake, it will be useful to give a low-sodium diet until a 15-16 kg/m(2) BMI. This should be integrated into the cognitive behavioral therapy.