248 CARNEGIE INSTITUTION OF WASHINGTON. 



5. With carbohydrates the basal metaboUsm may be increased to an aver- 

 age maximum of approximately 25 per cent by the ingestion of 100 grams of 

 any one of several sugars, although levulose and sucrose appear to exert a 

 somewhat more powerful influence than the other sugars. This increment 

 occurs inside of 2 hours and the metaboUsm has a tendency to return to the 

 base-Une somewhat rapidly thereafter. 



6. Ingestion of a diet containing a preponderance of fat produces a positive 

 increment in metabolism, although this increment is considerably less than 

 that observed with an equivalent amount of energy in either carbohydrate or 

 protein. 



7. Ingestion of protein in almost any quantity invariably produces an 

 increase over the basal heat-production, which may be 25 per cent for 

 several hours, and for short periods may rise to 45 per cent. No definite 

 mathematical relationship between the amount of protein ingested and the 

 increment in the total metabolism could be established in these experiments. 

 No clearly defined difference between the animal and vegetable proteins was 

 found in their influence upon the metabolism. 



8. Experiments with mixed diets, especially those with excessive amounts 

 of food, showed that by the ingestion of a large meal it was possible to stimu- 

 late metaboUsm to 40 per cent above the basal value for a number of hours, 

 and to 20 per cent for at least 8 hours; indeed, there was every reason to beUeve 

 that the stimulus to metabolism would have been found to continue consider- 

 ably longer than the experimental period of 8 hours if the observations had 

 been prolonged. 



The "cost of digestion," or the mathematical relationship between the fuel 

 value of the intake and the increase in heat-production due to the ingestion 

 of food, is estimated with carbohydrates to be not far from 6 per cent on the 

 average; with fat the increase is about 2 per cent of the fuel value of the intake, 

 with a protein-rich diet approximately 12 per cent, and with mixed diets 

 6 per cent. 



These experiments give no conclusive evidence regarding the cause of the 

 rise in metaboUsm after food ingestion. Brief mention is made of the three 

 prevailing explanations offered at present for this rise, i. e., the " Verdauungs- 

 arbeit" theory of Zuntz and his associates, the specific-dynamic- action 

 theory of Rubner, and the hypothesis that increase in heat-production is due 

 to a stimulus to the cells as the result of products (probably of acid nature) 

 obtained from the food materials ingested or elaborated from them. The 

 present series of experiments can not be used as experimental evidence for 

 any of the three current theories, although experience in the Nutrition Labo- 

 ratory points rather strongly in favor of the theory of acid-body-stimuli. 

 The report concludes with suggestions as to the best method for studjdng the 

 effect upon the basal metabolism of the ingestion of food or drugs. 



