C ORRESP ONBENCE. 



697 



CORRESPONDENCE. 



PROPER DIET FOR HOT WEATHER. 



Editor Popular Science Monthly. 

 rriHE article under the above title in your 

 _l_ July number appears to be based on 

 chemical theories of nutrition that find no 

 place in the modern science of physiology. 

 The classification of food constituents into 

 proteids or albuminoids, fats, and carbohy- 

 drates is a convenient one for certain pur- 

 poses, but it is now known that these groups 

 of nutrients have not the specific functions 

 that were formerly attributed to them. 



The assumption of Dr. Davies (page 366) 

 that " the foods that are converted into heat 

 that is, keep up the heat of the body are 

 starches, sugar, and fat, and those that more 

 particularly nourish the nervous and muscu- 

 lar system are the albumen and salts," is a 

 survival of an obsolete theory of respiration ; 

 and tables giving the proximate composition 

 of different articles of food are of little value 

 in formulating diets for special purposes. 



The law of the conservation of energy is 

 now recognized as a significant factor in all 

 physiological processes, and it furnishes the 

 only consistent explanation of the phenom- 

 ena of animal heat. The energy used in 

 the constructive processes is stored up as po- 

 tential energy, as an essential condition or 

 constituent of all organic substances, and on 

 their disintegration in the processes of de- 

 structive metabolism it is liberated in the 

 form of heat as in the digestion of foods, 

 and in the wear and tear of the tissues that 

 are constantly taking place in all vital activi 

 ties. 



Animal heat is no"t produced by a com- 

 bustion of certain food constituents that 

 serve as fuel, but it is the result of the libera- 

 tion of the stored euergy of foods and tissues, 

 iu the disintegrating processes they undergo 

 in the system. Dr. M. Foster, who is recog- 

 nized as one of the best authorities in physi- 

 ology, estimates the potential energy of food 

 constituents as follows : 

 1 gramme proteids = 4,500 calories, 



1 " fat =9,000 " 



1 " carbohydrates = 4,000 " 

 From this it appears that the " starches and 

 sugars," which are included in the group of 

 carbohydrates, contain less potential energy 

 than the proteids, and the heat obtained 

 from them is accordingly less. The infer- 

 ence that starch and sugar should be avoided 

 in hot weather, and largely replaced by lean 

 meat, which consists in the main of proteids 

 or albuminoids, is, therefore, not warranted 

 by the evidence in regard to their constitu- 

 tion. 



Without noticing the numerous fallacies 

 in the article in question, attention is called 



to the widely different conclusions reached 

 by Dr. Foster, in the last edition of his Physi- 

 ology, in discussing the adaptations of diets 

 to climatic conditions, and to the require- 

 ments of the system in brain-work and severe 

 muscular labor. 



He says : " With regard to climate the 

 chief considerations attach to temperature. 

 When the body is exposed to a low tempera- 

 ture, the general metabolism of the body is 

 increased, owing to a regulative action of the 

 nervous system. We might infer from this 

 that more food is necessary in cold climates ; 

 and, since the increase in the metabolism ap- 

 pears to manifest itself chiefly in a greater 

 discharge of carbonic acid, and therefore to 

 be especially a carbon metabolism, we might 

 infer that the carbon elements of food should 

 be especially increased. When the body is 

 exposed to high temperatures the same reflex 

 mechanism tends to lower the metabolism ; 

 but the effects in this direction are much less 

 clear than those of cold, and soon reach their 

 limits ; the bodily temperature is maintained 

 constant under the influence of surrounding 

 warmth not so much by diminished production 

 as by increased loss. We may infer from this 

 that in warm climates not less, but if any- 

 thing, rather more food than in temperate 

 climates is necessary in order to supply the 

 perspiration needed for the greater evapora- 

 tion and discharge of heat by the skin. . . . 

 Indeed, the evidence that the increase of 

 metabolism provoked by cold bears exclu- 

 sively on carbon constituents, is so uncertain 

 that it may be doubted whether any change 

 in the normal diet, beyond some increase in 

 the whole, should be made to meet a cold 

 climate. Similar reasons would lead one to 

 infer that man in the warmer climate would 

 maintain on the whole the same normal diet, 

 the only change perhaps being to increase it 

 slightly, possibly throwing the increase chiefly 

 on the carbohydrates with the special vievj of 

 furthering perspiration. . . . 



" In choosing a diet for muscular labor we 

 must have in view not the muscle itself but the 

 whole organism. And although it is possi- 

 ble that future research may suggest minor 

 changes in the various components of a nor- 

 mal diet, such as would lessen the strain dur- 

 ing labor on this or that part of the body, on 

 the muscles as well as on other organs, our 

 present knowledge would rather lead us to 

 conclude that what is good for the organism 

 in comparative rest is good also for the organ- 

 ism in arduous work ; that the diet, normal 

 for the former condition, would need for the 

 latter a limited total increase, but no striking 

 change in its composition. . . . The princi- 

 ples of such a conclusion with regard to mus- 



