Calories for maintenance of body weight 



BHE eats. — Although many of the animals 

 tended to gain weight throughout most of their 

 lifespan regardless of diet, there were often 50- 

 to 100-day intervals when weight remained rela- 

 tively constant. The caloric intake during these 

 intervals served as a basis for calculating calories 

 required for maintenance. The results available 

 are recorded in table 10. The values were ob- 

 tained for rats varying considerably in weight, 

 but in general included data for rats on each diet 

 with a similar weight range. On the basis of the 

 more extensive data obtained for rats fed SP 8 

 HVO diet, the calories required for maintenance 

 appeared to decrease with increasing age and/or 

 body weight. With rats fed SPE diet, however, 

 no such relationship appeared to exist. The 

 tendency for heavy rats on those diets with the 

 lowest maintenance requirement suggests that 

 there may be a real difference in the way that 

 these diets are utilized. The differences observed 

 in the average calorie requirements with diet, 

 however, were relatively small considering the 

 wide range of values observed for individual rats. 

 More data under controlled conditions of intake 

 and activity are needed to establish the significance 

 of these trends. 



Table 10. — Calories per gram of body weight per 

 weekjor maintenance of adult rats fed various diets 



Strain and diet 



Rats 



Calories per gram of 

 body weight 





Average 



Range 



BHE rats 

 SP 8 HVO_. 



Number 

 26 

 24 

 8 

 4 

 6 

 8 

 8 

 6 

 8 

 8 



7 

 5 



0. 98 

 . 95 

 . 90 

 . 96 

 . 90 

 . 95 

 .92 

 .89 

 .92 

 . 91 



.87 

 . 79 



0. 82-1. OS 



SPE 



. 73-1. 14 



SPM 



. 76- . 99 



SPB 



. 93- . 98 



SPPB 



SP 16 HVO- 



. 84- . 95 

 . 85-1. 13 



SP 8 lard . 



. 80-1. 05 



SP 16 lard 



. 79- . 95 



SP 8 butter . . . 



. 89- . 99 



SP 16 butter 



. 79-1. 04 



Wistar rats 

 SP 8 HVO 



. 83- . 96 



SPE 



. 73- . 85 







Wistar rats. — The lower calorie requirement 

 for maintenance of the Wistar rats fed SP 8 HVO 

 or SPE diets when compared with BHE rats 

 parallels the greater efficiency in their use of these 

 diets during early growth. In the young rats, 

 the differences were due in part at least to the 

 somewhat smaller body weight that was being 

 maintained during this period by Wistar rats. 

 A comparison of the weight and intake of the two 

 strains of rats fed SPE diet (appendix table 80) 

 shows a lower intake even by older Wistar rats 



during periods when the weight was as great as or 

 greater than that of BHE rats. 



Discussion. — Little information is available 

 on the energy requirements for maintenance of 

 the adult rat. Fixsen and Jackson (62) estimated 

 the requirement of the rat at 12.0 metabolizable 

 Calories per 100 grams per day for animals weigh- 

 ing 375 grams or less, and 11.5 metabolizable 

 Calories per 100 grams for those weighing more 

 than 375 grams. With two strains of rats, Palmer, 

 Kennedy, Calverley, and others (151) demon- 

 strated a difference in the utilization of foods for 

 growth and in the energy requirement for mainte- 

 nance. The high-efficiency strain of animals 

 stored a larger proportion of their food energy and 

 lost less energy as heat than did the low-efficiency 

 strain. These authors, using 4.1 Calories per gram 

 for protein and carbohydrate and 9.3 for fat, ob- 

 tained a value of 13.2 Calories per gram per day 

 for maintenance of the high-efficiency rats and 

 14.6 for the low-efficiency animals. Application 

 of these factors to the data reported in this 

 publication for BHE rats fed SP 8 HVO diet re- 

 sulted in a value of 12.7, similar to that of the 

 high-efficiency strain. Wistar rats appeared to be 

 still more efficient in their utilization of this same 

 diet for maintenance. 



Maximum body weight and diet 



Average weight curves provide little informa- 

 tion with regard to the variation in the rate of 

 gain or in the maximum weight attained by indi- 

 vidual rats. In table 11 are summarized data on 

 the average maximum weight and the range of 

 values observed for rats sacrificed between 300 

 and 500 days of age and for those that were older 

 than 500 days. These values include data for 

 rats scheduled for sacrifice in the age groups indi- 

 cated, as well as those from longevity studies, and 

 thus represent a relatively larger group of animals 

 for some of the diets than are included in table 9. 

 Data are also summarized for rats fed the various 

 supplemented SPE diets and for a small group of 

 rats fed SP 8 HVO and SPE diets from parents 

 raised on the Wistar stock diet. 



Although the average maximum weights ob- 

 served were generally higher, particularly for the 

 younger group of rats, than were apparent from 

 the average weight-age relationships seen in table 

 9, the results show the same general trend that 

 has already been discussed. Rats fed SPE diet 

 with the various supplements were similar in size 

 to those fed the unsupplemented diet. When 

 BHE rats were fed the stock diet on which the 

 Wistar rats had been fed, weanling rats tended to 

 be small and generally reached a maximum weight 

 on SP 8 HVO or SPE diet that was less than 

 that observed with these same diets when the 

 young were from parents raised on the usual stock 

 ration. 



Diet and obesity. — -Large rats were observed 

 with all of the experimental diets, particularly 

 with SPM or SPPB diet. The largest rat was a 



20 



