Hitherto, little attention has been paid to the possible influence of diet upon this faculty. It has always been assumed that endurance, like physical strength, is augmented by a rich proteid diet, but it has never been considered that diet by itself was a factor of any great moment as compared with training or persistent exercise. It is true that claims have been advanced from time to time concerning the beneficial effects on endurance of a vegetable diet, and vegetarians have frequently presented glowing reports of the great increase in endurance they have experienced, but little attention has been given to such statements, and the matter has remained more or less in obscurity.

Recently, Professor Irving Fisher,[63] of Yale, has conducted an interesting experiment on the influence of a change in diet on endurance, having the co-operation of nine healthy students as subjects. The experiment extended through five months, with endurance tests at the beginning, middle, and end of the period. At the outset, the men consumed daily an average of 2830 calories, of which 210 were in the form of flesh foods, such as meats, poultry, fish and shell-fish; 2.6 calories of proteid being ingested for each pound of body-weight. At the close of the experiment, the per capita calories had fallen to 2220, of which only 30 were in flesh foods, and the proteid had fallen to 1.4 calories per pound of body-weight. In other words, the total calories of the daily ration had dropped off about 25 per cent, the proteid about 40 per cent, and the flesh foods over 80 per cent, or to about one-sixth of their original amount.

To determine the endurance of the subjects, six simple gymnastic tests were employed, and one of mental endurance. The physical tests consisted of (1) in rising on the toes as often as possible; (2) deep knee-bending, or stooping as far as possible and rising to the standing posture, repeating as often as possible; (3) while lying on the back, raising the legs from the floor to a vertical position and lowering them again, repeating to the point of physical exhaustion; (4) raising a 5-lb. dumb-bell (with the triceps) in each hand from the shoulder up to the highest point above the head, repeating to the point of physical exhaustion; (5) holding the arms from the sides horizontally for as long a time as possible; (6) raising a dumb-bell (with the biceps) in one hand from a position in which the arm hangs free, to the shoulder and back, repeating to the point of physical exhaustion. This test was taken with four successive dumb-bells of decreasing weight, viz., 50, 25, 10, and 5 pounds respectively. The mental test consisted in adding specified columns of figures as rapidly as possible, the object being to find out whether the rapidity of performing such work tended to improve during the experiment.

The following table shows the results of the three sets of physical tests made in January, March, and June:

TESTS OF PHYSICAL ENDURANCE WITH THE NINE SUBJECTS

Time.B.E.Lq.Lw.M.P.R.T.W.
1. Rising onJan.30010073336912714827029001263
toesMar.40012652620654008311500
June500106130008515001800126318003350
2. Deep knee-Jan.821427048132208374129404
bendingMar.19147
June2008120258155230453250508
3. LegJan.25529223027502330
raisingMar.333440
June3338203531371031953
4. 5lb.Jan.751387838514410083185
Dumb-bellMar.106
(triceps)June1275980517556104101501
m. s.m. s.m. s.m. s.m. s.m. s.m. s.m. s.m. s.
5. HoldingJan.5–01–334–73–373–305–392–53–2211–0
arms hori-Mar.5–4915–35
zontalJune9–362–563–503–06–510–13–163–2423–45
6. 25lb.Jan.50181662011102554
Dumb-bellJune10510263330292775108
(biceps)

The data presented show a marked improvement in March and June over the record made at the beginning of the experiment in January, except in the case of one subject, E. As Fisher states, the increased endurance observed can be ascribed only to dietetic causes, since no other factors of known significance could have aided in the result. The dietetic changes, as we have seen, consisted in a slight reduction of the total amount of food consumed daily, but with a large reduction of the proteid element, especially from flesh foods. It is significant, says Fisher, that the only man whose strength and endurance showed any decrease was E, “whose case was exceptional in almost all respects. His reduction in quantity of food, except for a spurt at the end, was less than of most of the men; his reduction in proteid, with the same exception, was the least of all; his reduction in quantity of flesh foods was the least of all.” He stands out conspicuously as the one man whose endurance failed to improve. The mental test carried out with the subjects pointed to “a slight increase in mental quickness,” but the adding test was too short to be of great value.

We see in these results another confirmation of the view that the welfare of the body is not impaired by a marked reduction in the amount of proteid food; on the contrary, benefit results in the increased efficiency which manifests itself in various directions. Physical endurance is an asset not to be ignored, and like the strength of an individual, it may well be fostered by the recognition and practice of a principle which seemingly has a firm physiological basis. Whether the fatigue poisons come from the excessive exogenous katabolism of proteids in general, or whether they are derived directly in a measure from flesh foods, need not be considered here; the main point is that by lowering the rate of proteid katabolism, which necessarily compels a reduction in the amount of flesh foods, there is a diminished quantity of nitrogenous waste floating about in the body. Further, we need not criticise too closely the method by which the reduction of food is accomplished; whether it be by encouraging mastication, with a view to better tasting and fuller enjoyment of the food, to the point of involuntary swallowing; or whether we follow natural taste and appetite, reinforced by the use of reason, with a full appreciation of the principle that the welfare of the body is best subserved by a quantity of food commensurate with true physiological needs.

In making this presentation of the true food requirements of the body as based on the results of physiological experimentation and observation, I am by no means unmindful of the dangers of underfeeding; but this is a condition comparatively rare. When occurring, as stated by Dr. Curtis, “it is either because of dyspepsia, in which case it really is involuntary, or comes from some silly notion born of a combination of innate mental crookedness and that ‘little knowledge’ that is a dangerous thing.” Overfeeding is the predominant dietetic sin, and with the prevailing dietary standards, as fixed by common usage, there is good ground for believing that it will continue for many years to come. Reason tells us, however, in the practice of our personal nutrition, to steer a middle course between physiological excess on the one side, and the minimal food requirement on the other. To quote again from Dr. Curtis,[64] who has expressed the matter very forcibly, “The physiological chemist can easily draw a line on the Scylla (starvation) side of the channel. A dietary whereby the system gets less than it pays out is, obviously, a dangerous veer toward starvation rock. But on the Charybdis (stuffing) side, just as the whirlpool itself has no well-defined border, the channel boundary is not so easily marked. The case is exactly analogous to the stoking of a furnace. The proportion of ash to live coals is a telltale as to underfeeding, but not as to overfeeding. With undersupply of fuel the ashes overbalance the live coals, and the fire is thus foretold to be going out. But with an oversupply the fire simply burns the faster: all the fuel continues to be consumed; the more coal simply makes the more ash, so that equilibrium is not disturbed, although maintained at a higher level. To argue, therefore, that a given dietary is none too large, because the balance between the material receipts and expenditures of the economy is not upset, would be like saying that a given furnace-fire is certainly none too hot, since the ashes raked out of the fire-box just correspond to the amount of coal shovelled in. The same would be equally true of a slower fire consuming much less fuel. The philosophy of the matter is, then, to find the minimum of steam that will run the engine, and then maintain a fire somewhat hotter than the exact requirement, in order to run no risk of failure; or, to return to the metaphor already employed, the would-be careful liver must simply note how close to Scylla other voyagers have sailed with safety, and then steer his own bark accordingly.”

As one looks through the many careful dietary studies that have been made in recent years, it is easy to find striking illustrations of people, and communities of people, who have lived for long periods of time on dietaries so strikingly simple and meagre that it seems difficult at first glance to believe their daily needs could have been entirely satisfied. Yet, such observations are quite in accord with the facts we have been presenting, and they afford additional evidence that the artificial dietary standards that have been set up are widely at variance with the real requirements of the body for food. It may be quite true that many of the people referred to have been and are faddists, with peculiar notions regarding food, based on religious or other scruples, but that has no bearing on the main contention that they have lived for many years on amounts of food ridiculously small as compared with the ordinary customs of mankind. Thus, in Professor Jaffa’s report[65] of investigations made among fruitarians and Chinese of California is an interesting account of a dietary study of a family of fruitarians, consisting of two women and three children. They had all been fruitarians from five to seven years, their diet being limited to nuts and fruit, except for the addition of celery, honey, olive oil, and occasionally a small amount of prepared cereal food. This family was in the habit of taking only two meals a day; at 10.30 in the morning and at 5 o’clock in the afternoon. The first meal always consisted of nuts and fruit, the nuts being eaten first. At the second meal, nuts were usually replaced by olive oil and honey. The nuts made use of were almonds, Brazil nuts, pine nuts, pignolias (a variety of pine nuts), and walnuts. Fruits, both fresh and dried, were used, the former including apples, apricots, bananas, figs, grapes, olives (pickled), oranges, peaches, pears, plums, and tomatoes. The dried fruits were dates and raisins.