At the suggestion of Voit, who believed that the sudden withdrawal of carbohydrate from the food would increase protein metabolism and would explain the high tissue waste in diabetes, Lusk4 established himself in nitrogen equilibrium at two different levels. Withdrawal of 350 grams of carbohydrate from the diet increased the protein metabolism as appears below. The losses of body nitrogen are greater for the second day of change in the diet than for the first, since the metabolism at first remains under the influence of an ample glycogen supply which is available as a source of carbohydrate (see p. 72).

1 Consult Neuberg: "Oppenheimer's Handbuch der Biochemie," Ergan-zungsband, 1913, p. 569; Neuberg: "Biochemische Zeitschrift," 1915, lxxi, 1; v. Euler: "Neure Forschung uber alkoholische Gahrung, Fortschritte der Natur-wissenschaftlichen Forschung," 1914, x, 63.

2 Schwarz and Pulay: "Zeitschrift fur exp. Path, und Ther.," 1915, xvii, 383.

3 Masing: "Pfluger's Archiv," 1914, clvi, 401.

4 Lusk: "Zeitschrift fur Biologie," 1890, xxvii, 459.

Influence Of Carbohydrate Withdrawal On Protein Metabolism

These results may be compared with the later results of Thomas (see p. 155), who showed that protein containing 18.4 grams of nitrogen when given to a man did not maintain the body in nitrogen equilibrium when no carbohydrate was administered.

Tallqvist1 found that partial replacement of carbohydrate by fat in the diet may have no influence or only a transitory one upon the amount of protein metabolized. Thus, after establishing nitrogen equilibrium in man with a diet containing about 16 grams of nitrogen, 10 per cent, of the calories being in protein and 90 per cent, in carbohydrate, he replaced one-third of the carbohydrate calories with an isodynamic quantity of fat and obtained nitrogen equilibrium on the third day of the diet. This is of value in practical dietetics.

Zeller2 gave to a man a daily diet which contained very little protein and between 2700 and 3300 calories divided into different percentages of carbohydrate and fat. The protein metabolism of the body was not significantly altered until less than 10 per cent, of the total calories were given in the form of carbohydrate, i. e., butter, 360 grams; sugar, 70 grams; sauerkraut, 300 grams; tomatoes, 100 grams, containing 3300 calories. At this juncture, when, as Zeller notes, one molecule of monosaccharid is present for two of fat in the diet, aceton appeared in the urine in traces. When 5 per cent, of the calories were given in carbohydrate, aceton appeared abundantly in the urine, and when the whole of the diet consisted of fat calories there was a still higher aceton excretion, with an increasing ammonia production to neutralize the acid formed and the patient complained of weakness and discomfort.

1 Tallqvist: "Archiv fur Hygiene," 1902, xli, 177. 2 Zeller: "Archiv fur Physiologie," 1914, p. 213.

The following table epitomizes the results obtained:

If two molecules of fat are oxidized in the presence of one molecule of glucose (which assumes that the 3300 calories contained in the diet were liberated in metabolism), then one molecule of fat would be oxidized in the presence of one dissociated triose molecule. Each molecule of fat is made up of one molecule of gylcerin and three of fatty acid. Since glycerin is convertible into a triose, it is apparent that from glycerin and ingested sugar two molecules of triose are available for simultaneous oxidation when three of fatty acid are burned. Besides this, a small number of triose molecules may be derived from protein metabolized and another quota from stored glycogen. It appears from this analysis possible that the normal combustion of fat each molecule of -oxy-butyric acid, which is the end-product of the oxidation of each fatty acid, requires the presence of a triose molecule. Under these conditions the oxidation of fat would take place without acidosis and without increasing the metabolism of protein.

It is too early as yet to give a satisfactory explanation of the chemical reactions which might accompany this phenomenon. It may be noted that when protein is given in large quantity with fat the acidosis does not appear. This is understandable in view of the production of glucose from protein. One may also marvel at the fact that the "bread cards" issued in Vienna during the great war for 50 grams of bread daily per inhabitant can yield scarcely sufficient carbohydrate to prevent the occurrence of acidosis were bread the only food.

Zeller's experiments verify the conclusion that when the protein metabolism is reduced to a minimum, the elimination of creatinin nitrogen constitutes about 20 per cent, of the total quantity of urinary nitrogen (see p. 209).