The Specific Dynamic Action of Butter Fat, and of Superimposed Sugar

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Abstract
The specific dynamic action of butter fat, eaten as heavy cream, was studied in nine human subjects by means of the new semi-automatic respiration calorimeter, supplemented by the Tissot-Haldane method. Amounts of fat contained in the test meal varied from 80 to 171 gm. S.D.A. experiments occurred on the fourth or fifth day of an all-cream diet. For non-protein respiratory quotients less than 0.707, heat values for oxygen below the Zuntz-Shumburg table were found by the formula . The method assumes that all of the non-protein CO2 under these conditions comes from combustion of fat and that all of the extra oxygen is used for some other purpose than immediate combustion. Direct and indirect calorimetry agreed remarkably well, thus tending to confirm the assumption. Plausible S.D.A. curves showing the entire course of extra heat production over basal were possible for all subjects but one. The average S.D.A. expressed as a percentage of the fat calories fed was 4.74. Not more than 6% of the calory content was from other foodstuffs. The figures agree fairly well with those of Murlin and Lusk ('15) on the dog. There is no relation of S.D.A. to age, for lowest effects were obtained from the youngest and oldest subjects. It is, however, related to tolerance for fat, meaning not only capacity to digest but also capacity to metabolize completely. With six subjects sugar (sucrose or glucose C.P.7) was superimposed on the high fat at an ‘early’ interval (3 to 5 hours) after the fat meal was taken and the same amount again at a ‘late’ interval (11 to 15 hours), for the purpose of testing its combustibility. The dynamic response to the sugar was of two types, a) complete summation to the fat metabolism, and b) an increase greater than that due to the same amount of sugar fed alone; the difference is reckoned as fat metabolism. The extra heat may come in part from oxidation of ketone bodies induced by the sugar (see following paper). With three subjects the sugar, glucose, fructose and sucrose, respectively, was given twice at equal intervals after last fat and the combustibility and dynamic effects compared. There is no doubt from these experiments that a strong dynamic effect from sugar may be obtained without any evidence of its own combustion; where such evidence (higher R.Q.) was obtained there was no proportionality to the dynamic effect. The S.D.A. of fat does not appear to be due entirely to plethora in the sense of Lusk, for a) it does not run parallel to blood fat, and b) sugar superimposed causes increased combustion of fat.