ENERGY 505 



For starch ihe ralii) ol (aihoii dioxide prodiut'd to oxygen taken up 

 is 6X : GX (1.0), while the ratio lor the lat is 51 : 72.5 (0.70). Thus 

 these ratios are characteristic of the type of metabolite and suggest the 

 nature of material being utilized. They are called respiratory quo- 

 tients and are calculated from balanced reactions or from actual meas- 

 urements of the gases. 



Although the respiratory quotients differ somewhat for the different 

 members of each class of nutrient, the range is rather small. Ordinary 

 carbohydrates are all rather close to 1.0, fats to 0.7, and proteins to 

 0.8. Since standard diets are mixtures of all three, the respiratory 

 quotients observed with normal animals are averages weighted for 

 dietary composition. Special conditions lead to characteristic respira- 

 tory quotients. 



Fasting animals (juickly mobilize ami use up their carbohydrate 

 reserves. Thereafter the resj)iratory quotient is approximately 0.7. If 

 starvation is sufficiently prolonged, the depot fat will be depleted. 

 Use of body protein increases and the respiratory quotient rises somc- 

 Avhat. On the other hand, heavy intakes of carbohydrate lead to high 

 respiratory quotients as carbohydrate is converted to fat and stored. 

 This procedure diminishes oxygen uptake and increases the relative 

 production of carbon dioxide as some carbon atoms are reduced by 

 oxidation of others. The formation of palmitic acid illustrates the 

 point when written as follows: 



SCeHisOe + 702 -^ C16H32O2 + HCOa + UHoO 



glucose palmitic acid 



with a respiratory quotient of 2.0. Values of this sort have been ob- 

 served in hogs fed a mixture of starch and glucose. 



Low respiratory quotients occur in diabetes. This disease causes 

 extensive excretion of glucose and ketones, and formation of the lat- 

 ter represents incomplete degradation of fats to carbon dioxide. The 

 effect may be illustrated with palmitic acid. The carbon dioxide to 



C16H32O2 + I9O2 ^ CH3COCH2COOH + I2CO2 + I3H2O 



palmitic acid acctoacctic acid 



oxygen ratio in this case is 0.G3, a value below that normally obseived. 

 Thus it appears that respiratory quotients can reflect the dietary or 

 metabolic state of an animal. However, exact statements cannot be 

 made because diets are complex mixtures and because the relative 

 activities of the various pathways of the metabolic network are un- 

 known. As a result, representative balanced reactions cannot be chosen 

 to summarize the results of metabolism. 



Oxygen consumption may be correlated in another way with metab- 



