Estimation of protein intake: comparison of dietary assessment and urinary excretion

Estimates of dietary intake of nutrients have many problems, and confirmation of these estimates by chemical measurements of excretory products helps to establish their validity. The correlation between urinary amino acid excretion and dietary history of protein intake are reported herein. Diet diaries were kept by and 24-h urine collected from participants in the Trial of Antihypertensive Therapy and Management, a multicenter cooperative trial comparing the effects of drugs and diet on blood pressure control, side effects, and quality of life. The nutritional information was coded and the data stored by the nutritional analyses facility at Albert Einstein College of Medicine. The chemical determinations were done in the laboratories of the Department of Pathology, Izumo, Japan. The correlation between total protein and 3-methylhistidine was r = 0.42 (n = 96). The correlation was similar for animal protein (r = 0.4). These correlations are of the same order of magnitude as those between dietary sodium and urine sodium, and dietary potassium and urine potassium. We conclude that measurement of urinary protein excretion products may be a useful way to estimate dietary protein intake.