Objective verification of dietary intake by measurement of urine osmolality.

A new method for assessing the accuracy of dietary nutrient intakes in metabolic studies is described. The theoretical basis of the method is the comparison of measurements of the urine osmole excretion rate (OER, the product of urine osmolality and urine weight) with values for OER predicted from dietary nitrogen, sodium, and potassium. The method was tested in 34 healthy male and female volunteers aged 18-78 y who made complete 24-h urine collections and consumed a diet over 6 d in metabolic-balance studies involving either overfeeding, weight maintenance, or weight loss. The coefficients of variation for equations relating measured OER to dietary nitrogen, sodium, and potassium intakes ranged from 14.1% for 1-d measurements to 6.94% for 6-d means. These results indicate that it should be possible to use measurements of the urine OER to identify dietary noncompliance in metabolic studies.