In man, after the administration of 210 grams of butter, Magnus-Levy noted a maximal increase of 9 to 14 per cent, above the basal metabolism during the seventh hour. During the eighth hour the increase was only 6 to 8 per cent, above the basal metabolism.

The influence of external temperature on the heat production after ingesting fat above the requirement is similar to that after meat ingestion, only not so pronounced. Rubner1 gives the following table, showing the effect of the ingestion of 171.3 calories in fat per kilogram of dog:

Specific Dynamic Action Of Fat

At 2.70 the excess ingested above the requirement amounted to 12.6 per cent., and the increase in heat production was 2.2 per cent. At 310 the excess of food calories above the requirement was 165 per cent., and the increase in heat production was 23.9 per cent. In this instance 100 per cent, of the requirement may be calculated to raise the metabolism 14.4 per cent, at a temperature of 310. This represents the specific dynamic effect of fat on the metabolism.

Murlin and Lusk2 were not able to find so great a specific dynamic action in the dog as Rubner found. They gave to a dog an emulsion containing 75 grams of fat with 692 calories of energy, or 145 per cent, of the basal energy requirement of the animal. The total increase of heat production was 28.8 calories or 4.1 per cent, of the energy in the fat. The experiments were carried out at an environmental temperature of 260 to 2 70 in a respiration calorimeter, and the results are plotted in the form of a chart, as shown on p. 253. (For the effect of glucose and fat see also p. 300).

1 Rubner: "Energiegesetze," 1902, p. 119.

2 Murlin and Lusk: "Journal of Biological Chemistry," 1915, xxii, 15.

The experiment shows that after the ingestion of fat the heat production gradually rises till the sixth hour to a maximum 30 per cent, above the basal metabolism, and then falls slowly to the basal level, which is reached ten hours after the fat has been taken (Fig. 19). This curve of increasing metabolism accords with the curve of increasing fat content in the blood as shown by Bloor, and indicates that the heat production may be increased by increasing the number of metabolites available for cell nutrition.

Fig. 19. - The effect of fat and of glucose plus fat upon the heat production.

It appears from the respiratory quotients that the increase in heat production is entirely at the expense of ingested fat. The respiratory quotients as determined for the basal metabolism averaged 0.84, and after fat ingestion 0.79. Calculation showed that the amounts of protein and glycogen oxidized during the two series of experiments were identical, so that the extra heat production after giving fat was derived from fat itself.

It has already been demonstrated that less protein is burned in starvation when the body is fat than when it is lean. It would, therefore, seem that if protein and fat were ingested together, a similar reduction in the amount of the protein requirement would be effected (Voit).

It has been shown in a previous chapter that nitrogenous equilibrium can be maintained in a dog only after the ingestion of three and a half times the quantity of protein destroyed in starvation (seep. 154).

E. Voit and Korkunoff,1 continuing these experiments, find that if fat and meat be ingested together, the quantity of the latter necessary to establish nitrogenous equilibrium is reduced to between 1.6 to 2.1 times the starvation minimum. Much less protein food is, therefore, required to maintain the body's protein when it is ingested with fat than when it is given alone.

Thus Thomas2 could not maintain nitrogen equilibrium when twice the amount of the fasting nitrogen elimination was given to a man in the form of meat alone, but was able to accomplish this when meat to the extent of that destroyed in fasting was administered with fat. In consequence of this, protein is more readily added to the body when fat is ingested with it, as is seen in the following experiment of Rubner3 on a man:

1 Voit and Korkunoff: "Zeitschrift fur Biologie," 1895, xxxii, 117.

2 Thomas: "Archiv fur Physiologie," 1910, Supplement, p. 249.

3 Rubner: von Leyden's "Handbuch der Ernahrungstherapie," 1903, i, 43.

Influence Of Fat Ingestion On Nitrogen Retention

With increasing quantities of fat there is an increasing addition of protein to the body.

It has already been shown that protein ingested alone in large quantity establishes nitrogen equilibrium at a higher level, constantly raising the amount of heat produced until nitrogenous equilibrium is reached (the secondary dynamic rise, p. 233).

The same destruction of the easily oxidized protein takes place when it is given with fat, as was shown by Voit1 in the following experiment on a dog:

The "Secondary Rise" In Protein Metabolism On A Meat-Fat Diet

1 Voit: Hermann's Handbuch, "Physiologie des Stoffwechsels," 1881, p. 131.