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Minimum Protein Requirement of the Adult Rat for 28-Day Periods of Maintenance of Body Weight¹

Department of Biochemistry and Nutrition, School of Medicine, School of Tropical Medicine, University of Puerto Rico, San Juan

The minimum protein requirement in the adult rat for maintenance of body weight during 28-day periods was determined with a rice-beans-casein diet that had been employed to measure the minimum requirement for growth, reproduction and lactation. The following results were obtained:

1. The rat is in positive nitrogen balance during periods of maintenance of body weight.

2. The daily minimum protein requirement for maintenance of body weight is approximately 53 mg N per 100 gm body weight, regardless of sex or the fat content of isocaloric diets.

3. A 300-gm rat maintains body weight with a diet containing about one-half as much protein per calorie as that needed for growth, reproduction and lactation.

4. Since the "true" digestibility and biological value, determined under the conditions of the present experiment, were respectively 87.0 and 72.9, the daily net N requirement of these rats was 34 mg N per 100 gm body weight.

5. The minimum net protein requirement for maintenance of body weight appears to be 1.6 times that for maintenance of nitrogen equilibrium, and the ratio between these requirements is similar to the ratio between ingested calories during periods of body weight maintenance and those expended for basal metabolism.

Manuscript received 22 June 1951.