476 ANIMAL BIOCHEMISTRY 



desirable responses termed allergies in individuals absorbing such 

 protein materials from particular foods. Since food allergies appar- 

 ently follow the absorption of proteins, it is possible that the absorp- 

 tion of peptides is qiute common and that some of these are used 

 directly in protein syntheses, reducing the number of steps required. 



Protein Allowances 



Since proteins serve as the major sources of nitrogen, they must be 

 ingested regularly. This continuing need is perhaps more acute than 

 for either fats or carbohydrates, for as outlined on page 480 animals 

 are incapable of large-scale storage of proteins. Moreover, fats and 

 carbohydrates obviously cannot be converted to amino acids and 

 proteins without a supply of nitrogen. Therefore, it is probably more 

 important that proteins be eaten regularly than carbohydrates or 

 fats since the last two are more readily stored and interconverted. A 

 consumption of protein beyond the minimum requirement does not 

 seem at all harmful for the extra amino acids are metabolized by the 

 several routes to ammonium ion, urea, carbon dioxide, water, and 

 useful energy. As expected, the needs depend on the species, in- 

 dividual size, and physiological activity. 



Daily allowances for adult human beings have been set at 1 g. of 

 protein per kg. of body weight. This level amounts to about 70 g./day 

 for men near the average weight of 155 lb. and provides an excess 

 of perhaps 50 per cent above the minimum requirement. Some excess 

 is important to allow for differences in physical activity and especially 

 for differences in the effectiveness of different proteins. The ration 

 of about 60 g. of protein daily (dry-weight basis) for women should 

 be increased to 85 and 100 g. daily during pregnancy and lactation to 

 meet the elevated rates of protein synthesis. 



Children have relatively higher requirements because of their bodily 

 growth. Although not based on extensive experiments, the recom- 

 mended levels have been set at 3.5 g./kg. of body weight for children 

 up to 1 year old. Then the food should contain 40 g. daily to 3 years 

 of age with increments of 10 g./day added for each 3-year increase in 

 age, bringing the level to 70 g. daily at the age of 12. Girls of 12 to 20 

 and active boys of the same age have allowances set, respectively, at 

 75 to 80 and 85 to 100 g. of protein daily. 



Recommended protein levels for cattle range from 0.30 lb. /day for 

 50-lb. calves to 1.2 lb. for pregnant dairy cows and 1.4 lb. daily for 

 rapidly gaining beef cattle with weights of 800 lb. or more. The 

 detailed allowances are listed in the Appendix. 



Allowances for swine are exceptionally high because this species 



