Loewy And Zuntz, 1916

When the research reported by us in this monograph was more than half completed, we were fortunately able to secure a copy of the interesting article by Loewy and Zuntz3 on the influence of war diet upon metabolism. This gives the results of experiments made in the spring of 1916 in which the investigators themselves were the subjects. Inasmuch as both Zuntz and Loewy had had their basal metabolism measured intermittently for a number of years previous, their probable basal values are significant and afford an excellent basis for comparison with the metabolism determined after two years of war diet.

The experiments were made with the Zuntz-Geppert apparatus and represent (in the case of Zuntz) 5 periods on 3 different days in May 1916. In the case of Loewy they represent 4 periods on 2 days, also in May 1916. Although Zuntz had lost considerable body-weight, nevertheless the oxygen consumption and carbon-dioxide production were much lower per kilogram of body-weight than they were under pre-war conditions. The nitrogen excretion per day for Zuntz was relatively small, averaging not far from 6.50 grams. He computes that he was consuming approximately 51 to 52 grams of protein per day. Calculating the calories per square meter on the basis of the Meeh formula, he finds a reduction in heat production per square meter of body-surface corresponding to 7.3 per cent.

1 Morgulis, Biochem. Bulletin, 1914, 3, p. 264.

2 Hari, Biochem. Zeitschr., 1914, 66, p. 20.

3 Loewy and Zuntz, Berl. klin. Wochenachr., 1916, 53, p. 825.

With Loewy the loss in body-weight was not so great as with Zuntz. The oxygen consumption per kilogram of body-weight and per square meter of body-surface was considerably reduced, being 12.2 per cent lower per kilogram of body-weight than formerly. Unlike Zuntz, Loewy lived upon a reasonably liberal nitrogen intake, since the nitrogen in the urine averaged 13.95 grams per day. Taking into consideration the nitrogen in the feces, it is computed that the nitrogen content of the food was the equivalent of 97.6 grams protein, or nearly twice that of Zuntz.

As an explanation of this lowering of metabolism, the authors suggest two possibilities: one, that there was a greatly reduced protein intake; the other, that with the loss of body-weight there was an even greater percentage loss of active cell substance. They conclude that the first of these suppositions is disproved by the results obtained with Loewy, who partook of a fairly liberal nitrogen diet. They finally conclude that the main cause of the reduction is the loss of active cell substance and, further, that even if there is a fairly liberal protein intake in the diet, insufficient calories will cause a great loss of active body substance.

Observations of the pulse-rate with Zuntz indicate a slight falling off in the 1916 series of experiments. During this series hemoglobin determinations were made and showed that the blood of both men indicated 110 per cent of hemoglobin on the Plesch hemoglobinometer.

It is thus clear that these two German scientists have definitely shown in their own cases measurably lowered metabolism as a result of the loss in weight incidental to the restricted diet of war times. In our examination of the earlier literature nowhere do we find such clear-cut statements with experimental evidence of the possibility of lowering the basal metabolism of man as are seen in these experiments of Loewy and Zuntz. The conflicting evidence noted throughout the literature for animals and for pathological cases with man is entirely absent in these two series of experiments.

Jansen, 1917

The details of a second war-diet study, which was made by Jansen1 and confirmed the findings of Loewy and Zuntz, came to our attention only when the report of our research had reached the first galley proof and hence too late for extended analysis. With 13 subjects Jansen studied the influence of a low-calorie diet upon the nitrogen balance. All of the subjects, with the exception of two women in the group, had lost not far from 8 to 10 per cent in body-weight since the beginning of the war. The diet, which corresponded to the Munich ration in March 1917, had an energy value of about 1,600 (gross) calories per day, with a nitrogen content of approximately 9.7 grams (or 60.5 grams of protein) and contained 210 grams of carbohydrates. On this diet there was an average loss of nitrogen for the whole group of about 2 grams per day and an average loss in body-weight of 0.28 kilogram per day.

1 Jansen, Deutsch. Arch. f. klin. Med., 1917, 124, p. 1.

Respiration experiments were also made by the Zuntz-Geppert method with two subjects 23 and 26 years old, and of the same height and weight, i. e., 174 centimeters and 56.1 kilograms. The basal heat production per 24 hours found in these experiments was 1,338 calories and 1,456 calories, respectively, while on the basis of per kilogram of body-weight it was 23.8 and 25.0 calories, respectively. Jansen points out that these values are low as compared with Magnus-Levy's values for normal subjects of like weight1 and refers to the explanation of Loewy and Zuntz that this lowering in metabolism is due to the loss in active cell substance.

The basal metabolism of these subjects after a 3-day walking trip was again measured 12 hours after the last meal and after work and was found to be very greatly increased. The post-absorptive respiratory quotients for both subjects varied considerably, i. e., from 1.29 to 0.78 and from 1.10 to 0.86, respectively, whereas in the previous series of experiments the quotient had averaged about 0.87. The oxygen consumption likewise varied considerably with one subject, and the lung ventilation was greatly increased. Jansen concludes that this amount of exercise, which would not be considered at all strenuous with a well-nourished man, produced with these subjects on restricted diet an extraordinary exhaustion and affected the respiratory exchange even after 12 hours of repose, this being shown by abnormally high values for oxygen consumption and the respiratory quotient. Unfortunately the respiratory data, judged in the light of our own observations, seem to be of uncertain value. Such astonishing alterations in the respiratory quotient and, indeed, in the basal oxygen consumption, are outside of our experience. It is to be hoped that the data will be supplemented by publications from other European laboratories where metabolism studies on the influence of a reduced diet have doubtless been made.