344 - Mulficelluiar Animals, Especially Man 



weight decreases; and (3) it die energy of the 

 absorbed food is more than that expended, 

 the body weight increases. 



In recent times, metabolism tests involv- 

 ing a direct measurement of the heat output 

 have been supplanted by indirect calorim- 

 etry. When this method is employed, the 

 patient's consumption of oxygen and produc- 

 tion of carbon dioxide are accurately tallied 

 for a given length of time. These figures pro- 

 vide a basis for calculating not only how 

 much total food has been oxidized, but also 

 the proportions of the carbohydrates, fats, 

 and proteins that have been utilized. How- 

 ever, in addition to the oxygen and carbon 

 dioxide data, the output of urea and other 

 nitrogenous end products must be considered 

 if an accurate diagnosis of the patient's me- 

 tabolism is to be obtained. 



The Basal Metabolic Rate. The daily energy 

 expenditure varies widely, depending on the 

 general activity of a person, as well as upon 

 a variety of other factors. To obtain the 

 basal metabolism it is necessary to standard- 

 ize conditions very strictly. The subject must 

 fast overnight before the test, and must re- 

 cline in a completely relaxed condition dur- 

 ing the test. Also the age, weight, and bodily 

 proportions must be considered in establish- 

 ing the normal standards. 



For a man of average weight and propor- 

 tions (150 pounds, 5 feet. 8 inches, the nor- 

 mal basal metabolism is about 1600 Calories 

 daily. More than hall of this energy goes 

 toward maintaining the body temperature, 

 which is considerably above the usual en- 

 vironmental level. The main loss of heat is 

 from the body surface, and consequently the 

 bodily proportions are very important in 

 determining the proper standard. For short 

 stout individuals, the proportion of surface 

 to weight is at a minimum. Consequently 

 such a person has a normal basal metabolism 

 somewhat lower than 1600 Calories. 



The remainder of the basal energy ex- 

 penditure represents the work done by the 

 vital organs in the maintenance of life. The 

 heart must work ceaselessly, and this is also 



true of the muscles of breathing. Under basal 

 conditions not much work is done by the 

 musculature of the digestive tract, or of the 

 body wall, since the subject has been fasting 

 and is not maintaining an upright posture. 



In recent years measurements of the basal 

 metabolism are frequently used in medical 

 diagnosis. Abnormally high basal metabo- 

 lisms are encountered in patients with an 

 overactive thyroid gland (hyperthyroidism) 

 and in fevers. A low metabolism, on the other 

 hand, may indicate hypothyroidism; a defi- 

 ciency of the adrenal or pituitary glands; or 

 just plain undernutrition. 



Metabolic Rates under Other Conditions. If 

 the subject is allowed to eat, but remains in 

 bed, the metabolism rises to 1800 Calories. 

 The extra energy (200 Calories) goes mainly 

 into the secretory work of the digestive 

 glands, and to the muscular movements of 

 the digestive tract. However, the taking of 

 food, especially proteins, has a stimulating 

 effect upon general metabolism. When seden- 

 tary work as well as food is allowed, the 

 metabolism will average about 2400 Calories. 

 This additional energy (600 Calories) goes 

 mainly to the work of the both' muscles in 

 maintaining posture and in performing 

 daily routine movements. Under these cir- 

 cumstances, however, the work of the heart 

 is also greater, since a more active circulation 

 through the brain, muscles, and digestive tract 

 is required. A manual laborer will usually 

 expend from 3000 to 5000 Calories, depending 

 on the intensity and duration ot the work. 



Availability of Energy from Different Foods. 

 Disregarding the structural needs of the body 

 and reckoning only in terms of energy re- 

 quirements, one type of food may substitute 

 quite equally for another. A very high pro- 

 tein diet increases the daily output of nitro- 

 genous wastes and puts extra work upon the 

 kidneys; but the kidneys can safely handle 

 the extra load if they are in good condition. 

 Too high a proportion of fat (more than -10 

 percent of all the Caloric expenditure) is to 

 be avoided, however. Fatty substances do 

 not "burn" very completely when the tis- 



