The link between fluid intake and weight gain in psychosis.

Diurnal weight gain was found to be abnormal among 44 of 77 institutionalized chronically psychotic patients. All patients were weighed and urine samples obtained weekly for 3 weeks at 7 A.M. and 4 P.M. Diurnal weight gain was normalized as a percentage by subtracting the 7 A.M. weight from the 4 P.M. weight, multiplying the difference by 100, and then dividing the result by the 7 A.M. weight. Normalized diurnal weight gain (NDWG) was 2.504 +/- 1.266% for the 44 study patients with abnormal findings, .631 +/- .405% for the 16 acutely psychotic controls, and .511 +/- .351% for 29 normals. Urine excretion was related (r = .476, p = .001) to NDWG in the subgroup of study patients with abnormal NDWG, consistent with the observation that their fluid intake exceeded fluid excretion in the afternoon.