THE SIGNIFICANCE OF FATS IN THE DIET
Authors: E. H. Starling
Journal: BMJ (1918)

optimum reqiuirements of the average man for proteins, and the influence of the quality of proteins. Since, how ever, every mixed diet of sufficient energy value contains more than the minimum amount of proteins necessary for the maintenance of lhealth, the question is more academic tllan practical, and does not, tllerefore, present itself in considering the requirements of the individual rrman or of a nation. With regard to carbohydrates, ib has been established that a certain qulantity is essential. Sugar is the form in wbijih carbohydrates are put into currenev in thle system, and a certain amount of this substance appears to be necessary for the normal functioning of the cells of tlle body. In the absence of carbohydrates the proteins are attacked and carbohydrate is split off from the protein molecule, or syntlhetized from the oxy-fatty acids resulting from the primary decomposition of the amino acids. A diet in wlhich fat takes the whole place of carbolhydrates produces acidosis,-the oxidation of the fats being defective in the absence of carbohvdrates. The question as to the requirements of the body for fats and tlle significance of these substances in ordinary nmetabolisn bas, lhowever, been practically neglected, and it has needed the restriction of food supplies througlhout Europe, which is the immediate consequence of the war, to bring into prominence time great practical importance of the fat supply. Indeed, after lhaving provided the neces Pary calories for the maintenance of a population tlle only Tinpo-rfant question remaining is the provision of a proper amount of fat. Is it possible to arrive at a minimum figure for fat, or even a, minimum desirable amount, wlhich science can lay down for the guidance of those responsible for the feeding of the nation ? Scientific evidenc3 for the indispensability of fat in the diet is indeed very scanty. We lhave been accustomed to believe that fat and carbollydrate are convertible iso dynamically. We know that carbollydrate can be easily converted into fat in the body, and is thle main source of fatin the raisina of animlals for food. But in the case of carbolhydrates tllis isodynamy is limited. Some carbo hydrate is necessary for the health of muan unless he is to be reduced to partake of an abnormally large diet of protein for tlle sake of obtaining tlho necessary carbo hiydrate (as, for example, among the Esquimaux). Is there any evidence of a similar limit in the case of f.tt? For th]e adult man we lhave a mass experiment in Germany, whIere the population lhas suffered for th1e last two years or more from a marked shortage of fat, whiCIh has been reduced in the towns to About ZO grams a hiead a day. In thlis case certain diseases have occurred whiCh1 hiave been ascribed to the deficiency in fat and hiave been cured by increasing the fat in the diet. These morbid conditions are marked by a generalized dropsy. It has long been known that a sudden.chIange froIm a mainly fat to a mainly carbohjydrate diet causes an immediate increase iii weighlt, due not to the putting on of fat but to th1e Irtention of water in the body, and the dropsical condition occurring ;i Germany would seem to be due to thle same fLctor in au exaggerated form. Similar cases occurred in s)me asylums in this country during tlhe mild fat shiortage fimom whichl we suffered dutring the early part of thlis yea. h'lhe pathiological effects of' fat slhortage are especially i!iarked wlhen there is a reduction of the total food supply, so tllat tllere is aeneral deprivation of food as well as the special deprivation of fat. According to Hindhede, it is -ossible to maintain health, in the almost entire absence of fat, on a full diet in whlichl potatoes and greenl foods are )redominant features. But a deficiency of fat inl thle diet will almost always be associated with and due to a shlortawge of food supplies genlerally. In babies rickets is associated by some with deficiency of fat in the diet. In this case a more important factor seems, lhowever, to be an absence of some food lhormone or vitamine associated with butter, cod liver oil, and many otlher kinds of fat, and, according to lbellanby, it cannot be cured except by giving a fat containing bhe substances in question. Thle absolute physiological need of the cells of the body for fat supplied as such seems, therefore, to be unproven in view of the capacity of the body for manu facturing fat out of carbohydrates given in excess of the phlysiological requirements for energy. Th'is con clusion, however, does not mean that fat is unnecessary in a normal diet; several other points have to be taken into consideration. In the first place, fat is higlhly assimilable and is almost entirely absorbed from the alimentary canal. Hut it is digested and absorbed more slowly than carbohydrate. Whereas the greater part of the latter is absorbed three hours after food hias been taken, the most intense absorp tion of fat occers between five and six hours after a meal. On this account a meal lacking in fat is deficient in staying power. Man is unaccustomed to working with the ali mentary caual eintirely at rest. When digestion of tlle last meal is finisled hunger recurs and affects the efficiency of work. Thus Major Ewing relates how on a railway job in Canada the Italian workmen were found to become inefficient at about 11 o'clock in the morning. These workmen were only spending 7 to 8 dollars for food at thie canteen as against 15 dollars expended by the Canadian workmen. The chief difforence in the diet conditioned by this economy was in the meat. rhe company then insisted on the Italians spending 15 dollars a monthl. With the extra money they bouglht fat beef, and it was then found that their work was entirely satisfactory. It may be objected that in this case it was the lean of meat, that is, the extra protein rathor than the fat, whlielh was responsible for the difference; but examiination of the dietaries of very heavy workers-for example, lumbermen in Sweden and in Canada, who were consuming food with a calorie value of 4,000 to 8,0(X0 calories a day-shows that this great increase in food related not to the protein but to the fat. The Canadian lumbermen live largely on fat pork and beans. In this country, too, there have been complaints from the Welsh miners during the first lhalf of this year that the food hiad not enabled them to work tlheir normal shifts. They are used to taking witlh tlhem to tteir' work pies made of fat pastry with a little meat, and it was impossible to make the pastry in conse quence of the absence of fat. Premature lhunger was also a universal experience in this country during the first five montlhs of this year. In the second place, the bulk of food must be of con siderable importance, especially when the total food re quired by the energy needs of the body is very large. Weig,ht for weiglht fat lhas more tllan double the calorie value of starch and sugar. But the difference in bulk is still greater, since fat is taken withunt adumixture in a pure formn, whereas the other foods are all mixed witlh a considerable proportion of water, The proteins in meat only form 15 to 20 per ce-nt. of the total bulk. Starch cannot be taken except miixed withl Iarge quantities of saliva. When ordinarily cooked it is swollen up witlh probably five to ten times its amount of water. Even after absorption the same necessity for increasing the bulk of carbohydrates witlh water persists. Even glycogen does not occur to a larger amount in the liver than 12 per cent., a figure which may be larg,ely surpassed by fat, and iii adipose tissue tllere may be as muclh as 80 per cent. of fat. Wlhen carbohydrate goes into the circulation it is clhanged into sugar, and as sugar it needs twenty timnes its weiglht of water to carry it. It acts, therefore, to some extent in the same way as common salt. Just as an extensive diet of salt may produce dropsv, so a diet of carbohydrate increases in thle first place the water content of tlle body, and this factor, when associated with inanition and fat shortage, may itself produce actual dropsy. The question of bulk is probably one of the most im portant factors in determining the need for fat. Thle human alimentary canal has been developed so as to cope withl a diet in whlichs 20 to 25 per cent. of the energy is presented in thle form of fat. In order to get thle samle energy from carbohlydrates thle alimentary canala [3005]