Diurnal weight gain among patients with mental retardation. 
We compared the diurnal weight gain of 46 patients with mental retardation to that of 21 patients with organic mental syndromes.  They were weighed at 7 a.m. and 4 p.m. weekly for 3 weeks.  We normalized the diurnal weight gain as a percentage by subtracting the 7 a.m. weight from the 4 p.m. weight, multiplying the difference by 100, and dividing the result by the 7 a.m. weight.  Normalized diurnal weight gain was abnormal among one fourth of patients with mental retardation and two thirds of those with organic mental syndromes.  Differences in age, sex, baseline weight, antipsychotic drugs, lithium, carbamazepine, blood pressure, and pulse did not explain our results.  We believe that our findings provide additional evidence to separate patients with mental retardation from those with psychosis.