IV. Combustion Processes - Fasting and Undernutrition

The development of energy is not materially altered in acute inanition; the absolute amount of energy developed, it is true, becomes reduced (external conditions being equal) with the reduction of the weight. Calculated per kilogramme, however, the total energy development expressed in calories is only slightly reduced.

Tigerstedt in a man who fasted for five days found the following:

In investigations of this kind the total caloric de velopment is best calculated from the quantity of oxygen consumed. The technique of this method of investigation has been worked out so thoroughly that now-a-days such determinations can be performed with all necessary precision. If no carbohydrates are consumed, and this is the case in a fasting individual, then the consumption of one liter of oxygen demonstrates that 4.7 calories were developed.

Respiratory metabolism and the total development of heat, therefore, proceed exactly in the same manner in fasting as in complete nutrition. The only difference is this: that in inanition the necessary amount of energy is derived from the combustion of the body tissues proper, whereas under normal conditions the food constituents should be the source of this energy.

In undernutrition in which one part of the caloric demands is supplied by the food, another part by the sacrifice of body tissues, conditions are similar. This may be considered established at least for early periods of undernutrition. There remains to be discussed merely the question whether or not with sinking of the body weight and sinking of the albumin contents of the body, a sort of adaptation occurs; in the sense namely, that the total development of energy becomes correspondingly reduced. This would constitute a conservative process of economy. The existence of such relations becomes apparent when the total number of calories developed is calculated. Assuming that a well-nourished individual undergoes chronic undernutrition until he has lost 30% of his original body weight, then he will require 30% less food intake to maintain this reduced weight than he would have required to maintain his original weight. This relation becomes especially clear in studies performed on individuals undergoing climbing tests. A person weighing 100 kg climbing an elevation of 1000 m performs a labor of 100000 kgm; an individual weighing 50 kg mounting to the same elevation develops 50000 kgm. The amount of energy actually consumed is approxi mately three times this amount (300000 and 150000 kgm), for a human being is capable of transforming only one-third of the developed energy into external labor. In the first instance the rise to the elevation demanded the development of 706 calories, in the second of 353 calories (1 calorie = 425 kgm).

The relative development of energy, i. e., the number of calories developed per kilogramme of body weight, remains approximately the same in adequate and inadequate nutrition, leaving aside certain unimportant exceptions that need not be discussed in this place. One can predict with almost mathematical accuracy what loss of weight will occur from a definite degree of undernutrition. We will assume that an individual weighing 70 kg requires 40 calories per kilo of body weight in order to maintain nutritive equilibrium. Taking into consideration his occupation and method of life, we will now assume that instead of getting these 2800 calories per diem, he is forced for some reason or other to live on a diet containing only 2400 calories. The expenditure per kilo remains the same; and he will therefore be forced to develop the deficit of 400 calories from his own tissue substances, and he will continue to emaciate until his weight has been reduced to about 60 kg. When this point has been reached the balance has been re-established between the calories introduced with his food (2400 calories) and the calories that he must develop according to his body weight to maintain nutritive equilibrium. So long as his diet and the external con ditions of life remain the same, he will not emaciate on this caloric intake.

This form of calculation applies to the great majority of cases. Only in extreme degrees of emaciation do exceptions occur, for here a greater amount of energy must be developed per kilogramme of body weight than in a less reduced state of nutrition. The reasons for this will be discussed in the third lecture.

Generally speaking, the relative development of energy in an emaciating and an emaciated individual must be calculated in the same way as in an individual in a normal state of nutrition.

From 30-35 calories pro kg when resting in bed From 32-35 calories pro kg when remaining quietly in doors From 35-40 calories pro kg when performing a light amount of physical exercise (city dwellers)

From 40-45 calories pro kg when performing a moderate amount of physical exercise From 45-60 calories pro kg when performing very severe labor

A diet that answers these requirements we call a "Maintenance Diet" ("Erhaltungskost"). If the diet remains below the above indicated caloric value, then we have a condition of under nutrition, and the inevitable result will be a more or less pronounced degree of emaciation.