Heretofore, it has not been possible to measure the heat production of individuals leading their usual lives, due to the unavoidable restrictions necessary to carry out either direct or indirect calorimetry. It is quite obvious that the movements of a subject in a calorimeter are sharply restricted by the capacity of the apparatus and, hence, prevent normal activity. On the other hand, the value of determinations based on indirect calorimetry depends on sampling in such a way that the expired air thus collected is really representative of the period, and there is no way of knowing whether this is the case. Further, the sampling necessarily requires the individual to be at rest for frequent ten minute periods and so disturbs his usual routine. The method which we are proposing is not hampered by either of these two restrictions.In an earlier paper (1) it was pointed out that the insensible loss of weight is roughly proportional to the heat production of the period, provided two sources of error are excluded; namely, first, there must be a proper relationship between the rate of heat production and the environmental conditions, and, secondly, the subject must be transforming a minimal amount of energy to mechanical work. In the previous paper it was also shown that the insensible loss of weight is the resultant of the weight of water lost by evaporation, the weight of exhaled carbon dioxide and the weight of absorbed oxygen. The relationship can be conveniently expressed as an equation:Insensible loss of weight = H20 + CO2 -02.
In 1911, and several times thereafter, Grafe and his associates (1) stated that the fasting, resting metabolism of an individual is not proportional to the surface area, but is significantly affected by the calorific value of the food previously ingested. They also postulated that the total metabolism is influenced in the same way by the total intake of energy. According to them, normal animals, including man, maintain a constant weight, almost without regard to the energy intake, and obesity is often nothing more than the failure of this alleged mechanism to respond normally to the stimulus of food. Finally, leanness is an over-response to a normal stimulus.They supported these views by the following type of experiments: A dog was starved for a long time, and its resting, fasting metabolism was then determined. This value was used as the basis for comparison. The dog was now offered an abundance of food, and gained weight rapidly. The metabolism was repeatedly determined in the fasting, resting state. The metabolic rate thus determined showed a progressive increase out of proportion to the increase in body surface. Table I sets forth their data in detail, rearranged by us.This increase in metabolic rate of the overfed animal beyond that of the starved animal was accepted by them as proof that the resting, fasting metabolism of the normal animal is increased by previous overfeeding. But the metabolic rate obtained after prolonged starvation should not have been accepted as a proper basis for comparison, since Schondorff (2) had previously shown that starvation caused a decrease I The expenses of this investigation were defrayed in part by a fund for the study of nutrition, created by
An earlier publication from this laboratory (1) dealt with the measurement of total water exchange. In the interval, the application of this method has given rise to a number of modifications which increase the accuracy of the results obtained, so that it appears advisable to discuss the subject again.In a recent article (2), we have shown that the method of Benedict and Root (3) for the estimation of basal heat production from the insensible loss of weight, is subject to rather large errors. On the other hand, we have pointed out (4) that the determination of the amount of water vaporized in twenty-four hours gives an accurate method for estimating the total energy exchange in individuals under conditions of normal activity. This paper will deal with the water balance in one of these individuals on two different diets, since this data is well suited for the discussion of the principles involved. A portion of the data of this experiment is being reported in another publication (5).The estimation of water balance necessitates the direct determination, or the calculation of, four sources of water to the organism, and of three means of excretion of water from it. The factors involved in water balance may be advantageously listed as follows: Excretory waterSources of water
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