Evaluation of Dietary Protein Quality in Adult Rats

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Abstract
The usefulness of the slope-ratio technique for the evaluation of the nutritional quality of proteins for maintenance rather than growth has been examined using adult rats. Of the four proteins examined, lactalbumin, casein, soy protein, and gluten, the first three produce the responses expected. Gluten, low in lysine, is much more efficiently utilized for maintenance than for growth. Apparently there are mechanisms which permit a relative conservation of body protein when proteins low in lysine (and perhaps other amino acids) are fed at or below maintenance levels. The inadequacies of the slope-ratio method for the evaluation of such proteins are shared by the measurement of biological value, net protein ratio, and net protein utilization. The general applicability of amino acid scores is also questioned since the patterns of amino acids required for growth and maintenance are apparently different. Estimates of the amount of different proteins required for maintenance may be derived from the dose-response regression lines.