Obesity: Overnutrition Or Disease of Metabolism? A

268 OBESITY: OVERNUTRITION OR DISEASE OF METABOLISM? A. W. PENNINGTON, M. D., Wilmington, Del. LTHOUGH IT IS widely believed that physio- jeered to sul;caloric diets; and in the other, normal- A logical experinaents have proven the absence of weight individuals have first increased their weight by any metabolic defect in the etiology of obesity, a clear- purposeful overfeeding and then lowered their caloric cut analysis of the manner in which they are presumed intake. The effects of caloric restrictitm on metabolically to have done so is difficult to find. Discussions of the normal individuals under these two circumstances subject often emphasize that the energy intake must form a background for evaluating the effects of caloric exceed the expenditure when obesity is developing; restriction on individuals in whom obesity has arisen, but this elementary knowledge, deducible from the as it ordinarily does, spontaneously. Table 1 shows the law of conservation of energy, needs no experiment. effects of caloric restriction on the basal energy ex- The question on which an experimental answer has penditure of individuals of normal weight subjected been sought is whether the positive caloric balance to undernutrition. associated with obesity arises from causes extrinsic to the metabolism or from some intrinsic metabolic defect. TABLE I Many experiments have failed to reveal any naeta- AVERAGE DECLINE IN ENERGY EXPENDITURE OF bolic alteration froni the normal in obesity. Basal me- INDIVIDUALS OF NORMAL WEIGHT, DURING tabolism tests have ruled out disease of the thyroid UNDERNUTRITION gland; and many explorations of the intermediary me- Nol~r('e Decline in basal Decline in tabolism have given negative results. Since, however, calorics B.M.R. these do not rule out the possibility of some still un- Benedict (Squad A) (1) 19 per cent 16.2 per cent discovered defect, studies of the energy exchange have attempted to answer the essential question whether or Be:wdiet (Squad B) (1) 32 per cent 27 per cent not a metabolic aberration can, at all, account for Taylor and Keys (2) 39 per (.ent 31.2 per cent obesity. Studies of the energy exchange might well be ex- It is apparent from the table that a varying but sig- pected to answer this crucial question by showing nificant decline in energy expenditure occurs when whether the excessive energy storage of the obese is people of normal weight are subjected to subcaloric nu- causally dependent on the balance between energy in- trition. This would indicate that the normal energy take and expenditure or if it maintains a significant stores of the body maintain a considerable degree of degree of independence of that balance. In either case, independence of the energy balance. It would seem to the necessities of the energy equation, coincide with evidence from other sources that the normal energy stores of the body are regulated by in- energy intake = energy storage q- energy expenditure, trins;c metabolic mechanisms (3). They are not yielded nmst be fulfilled. In this equation, energy storage may for energy in an amount equivalent to the calorie be positive or negative in sign. Experimental investi- deficit of a subcaloric diet and, as a result, there is seen gation of the matter has been attempted by altering the "specific reduction in metabolism coincident with the energy intake and observing the effect of this on undernutrition" (4). energy storage and expenditure. If the excessive energy Table 2 shows the effects of reduction in the cal- stores of the obese depend passively on the balance oric intake on the basal energy expenditure of two nor- between energy intake and expenditure, caloric re- mal individuals who first increased their weight by striction should be followed by utilization of stored en- purposeful overfeeding. ergy in an amount equivalent to the calorie deficit of the diet, with no more decline in energy expenditure TABLE II than would be anticipated from the reduction in body EFFECTS ON THE BASAL METABOLIC RATE OF weight. If, on the other hand, the excessive energy PURPOSEFUL OVERFEEDING AND SUBSE- QUENT CALORIC RESTRICTION IN NORMAL stores arise from some intrinsic metabolic aberration, INDIVIDUALS they would be expected to show a significant degree of independence of the balance between energy intake and energy expenditure; caloric restriction, in such a .~ "~. ~ % ~ % case, would not be followed by utilization of stored energy in an amount equivalent to the calorie deficit of the diet, and the energy expenditure would show a significant decline CONTROL STUDIES ON NORMAL INDIVIDUALS Gulick(5) 0% 0% 0% 0% 0% Two types of energy balance studies on normal in- Wiley & -10% -4.1% -11.3% 7.2% 1.3% dividuals serve as controls for studies on the obese. In Newburgh (6) one type, individuals of normal weight have been sub- Medical Division, E. I. duPont de Nemours and Co., Wil- 11a Gulick's case, which showed a remarkable steadi- mington, Del. ness of the metabolic rate, there was a weight gain of AMER. JOUU. Din. Din. O~ESITY" OVERNI'TRITION ()R DISEASE OF ~IETABOLISM? 269 26 pounds during the course of 11 months before caloric however, the experiments were not checked by actual restriction. In the case of Wiley and Newburgh there determinations of the energy expenditure after caloric was a weight gain of 9.7 pounds during 2 weeks of restriction, the results would appear to depend entirely very intensive overfeeding before the reduction in on the value assumed for the water content of body fat. caloric intake. The rise and fall in basal metabolism Lauter had determined this to be 10 per cent, but in this ca.se may reasonably be attributed to the tem- Bischoff had found it to be 29 per cent, Bozenraad 7 to porary increase in lnetabolism representing energy uti- 46 per cent, and Bozenraad had quoted others who lized in the metabolic work of adding flesh to the body; found it to vary between 15 and 30 per cent (9). during the rapid fattening of steers the basal metabolism If the water content of body fat is higher than New- may rise as much as 36 per cent (7). The more pro- burgh supposed, a smaller quantity of stored energy longed experiment of Gnlick would seem to have elim- must have been yielded by the fatty det)osits than inated this temporary effect by allowing time for a would be indicated by his calculations from the weight levelling off of the weight at the higher level. The Io:ss. In view of the uncertainty concerning the water evidence from these experiments would seem to indi- content of body fat, it seems that no conclusions con- cate that, in metabolically normal individuals who have cerning the nature of obesity can be drawn from New- increased their weight by purposeful overfeeding, the ex- burgh's studies of the energy exchange. cessive energy stores are passively dependent on the bal- Actual determinations of the energy expenditure of ance between energy intake and expenditure; for these the obese after caloric restriction have shown that stores respond to caloric restriction by yielding their there is a significant decline. Table 3 gives the basic substance for energy in an amount equivalent to the data from sources frequently referred to. calorie deficit of the diet, with the result that no signif]- cant decline in energy expenditure occurs. Although the TABLE ]lI normal energy stores of these subjects were presumably maintained by the same intrinsic mechanisms which AVERAGE DECLINE IN ENERGY EXPENDITURE ()P OBESE ADI'LTS ON LOW CALORIE DIETS operate in other normal individuals, their excess stores were obviously dependent on causes extrinsic to the metabolism. These individnals, when allowing the appetite to regtflate the food intake, lnaintained con- stant weight at a normal level. STUDIES OF THE t?~NERGY EXCtIANGE IN OBESITY Strang and Evans (10) 14 per cent If the excessive energy stores in colnmon obesity, Brown and Ohlson (11) 17 per cent which ordinarily arise spontaneously, show a passive Lyon and Dtl~llop (9) 1.3 per cent dependence on the energy balance, as do the excessive stores of normal individuals in purposeful overfeeding Kecton and Bone (12) 12.2 per cent (calculated from graph) experiments, their maintenance nmst be attributed to causes extrinsic to the metabolism, and the cause of Mollcr (13) 12.5 per cent obesity must he simple overfeeding. If, 'on the other (calculated from graph) hand, the excessive energy stores of the obese show a significant degree of independence of the energy bal- In children, according to tables furnished by Muller ance, as do the normal energy stores of the body, their and Topper (14), the decline in B.M.R. is less, but maintenance must be attributed to an intrinsic mechan- the authors point out that the pelidisi of Pirquet is a ism, and the cause of obesity must 1)e a metal)olic better measure of energy expenditure in children than aberration involving the regulation of fat storage. is the usual surface area rule. The evidence from the basic data of all of the investigators would seeln to Experiments showing the effects of caloric restric- indicate that, in the adult obese individual, caloric re- tion on the obese have been of two types. In one, efforts striction is followed by a significant decline in energy have been made to determine the amount of body expenditure, for the decline is greater than the decline substance oxidized; and in the other, efforts have been in either the weight or the surface area (9) (15). made to determine whether or not there has been a decline in the energy expenditure. Since oxidation of EVALUATION OF TIIE RESULTS body substance offsets a decline in the energy expendi- The decline in energy expenditure of the obese ture, the two quantities are inversely related.

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