178 II. DIGESTION AND ABSORPTION OF FATS 



that it is related to the amount of fat present in the intestine. As the quan- 

 tity of fat decreases, the rate of absorption decreases in a parallel manner. 

 While there is some indication that an increased rate may obtain when 

 excessively large amounts of fat are fed to rats, 614 this probably is not a valid 

 explanation for the differences noted when fat is fed at the level of 300 mg. 

 per 100 sq. cm. of body surface. Another fact which argues against this 

 second explanation is that, in a number of fats, the rate of absorption is 

 relatively constant over a long time interval. 



The results obtained when the fat absorption is determined on the per- 

 centage basis 611 would seem to be in the same range as when it is calculated 

 on the surface area basis. 612 ' 614 However, the figures calculated in Table 22 

 for absorption in mg. per 100 sq. cm. per hour are mere assumptions. 

 Since the weights of the rats are not given, it is impossible to calculate 

 surface area. However, Irwin et al. 6U state that rats weighing from 200 to 

 400 g. can be used. Our calculations are based upon rats weighing approxi- 

 mately 300 g. If the average weight of the rats was 200 g., then the calcu- 

 lated values are about 33% too low; if, on the other hand, the body weights 

 averaged 400 g., the calculated values in Table 22 are 25% too high. 



It is a moot question as to what relationship exists between the rate of 

 absorption and the nutritional value of fat. In the first place, when a fat 

 is absorbed at a rapid rate, large amounts can be tolerated without produc- 

 ing diarrhea. On the other hand, this rapid absorption of fats might more 

 readily bring about an alimentary lipemia. 



In the case of fats which are more slowly absorbed, one can argue that 

 the presence of the fat in the gastrointestinal tract for a longer period has a 

 beneficial effect in that it may extend the period of absorption and thus 

 entail less of a burden on the organism. It is only when the rate of absorp- 

 tion of the fat is so slow that this process cannot be completed before the fat 

 reaches the lower gut (and hence is lost in the feces) that the rate of absorp- 

 tion of fat can be considered a function of its nutritional value. 



9. Factors Affecting the Rate of Absorption of Fats 



(./) Age and Sex 



Irwin et al. 611 report that, within the limits of their experiments, covering 

 four to seven months, age was not found to be a factor in fat absorption in 

 rats. However, due to the technic employed by these workers, namely the 

 administration of 1.5 ml. of fat irrespective of the size of the animal, a 

 marked discrepancy in the percentage of fat absorbed in a given time is 



