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

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

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.

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.

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.