Protein Nutrition in Aged Individuals on Self-Selected Diets

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Abstract
The purpose of this study was to estimate the habitual protein intake of subjects aged 75-85 and to relate this intake to indices of body protein content and of well-being. In 15 subjects, daily nitrogen intake was measured (M) in duplicate diets and estimated (E) from the mean nitrogen content of three 24-hr urine collections plus average daily stool nitrogen. The relationship was M = 2.23 + 0.77E, seEst = 1.59, r = 0.71, P < 0.01. Correlations of the measured dietary nitrogen with estimates by diet observation (r = 0.59, P < 0.02), diet history (r = 0.51, P > 0.05), and casual urine N-Cr ratios (r = 0.34, P > 0.2) were lower. Estimates of daily protein intake by means of 24-hr urine collections were made in 28 more subjects (total subjects: 28 men, 15 women). Data were adjusted to a reference height. Protein intakeREF HTranged from 41 to 80 g in men and 33 to 60 g in women and formed from 8 to 24% of total calories. Significant correlations were not found between protein intake and serum albumin, total plasma amino acids, lean body mass (whole body K40), metacarpal bone cortical thickness, or dorsal hand skin-fold thickness. In women (r = 0.95, P < 0.01) but not in men (r = 0.29, P > 0.3) protein intake correlated with activity and well-being as measured by questionnaire scores. The data do not suggest an adverse effect in the aged, of low protein intakes on body protein content. Protein intake may relate to other aspects of health, but whether it is cause or effect is not presently clear.