Nutritional Deficiency and Stomach Contraction

Results from various lines of experimental work indicate conclusively that the physiological basis of the hunger excitant is found in the contractions of the smooth muscles of the stomach wall.

There is considerable reason to believe that the typical hunger contractions are not initiated spontaneously by an empty or partially empty stomach but are due to some chemical stimulus acting directly upon the stomach walls. When food is present, a variety of digestive fluids and ferments is secreted by small glands lying within the stomach wall. It is possible that in the absence of absorbent food substances these fluids act directly upon the stomach walls to cause contraction; at least, similar fluids, such as weak hydrochloric acid, will cause contraction when introduced into the stomach by way of the mouth. It is possible also that chemical stimuli carried by the blood act as excitants to contraction. The chemical disequilibrium of the body may be upset by a nutritive deficiency in the bodily tissues, and that the deficiency products in the blood act directly on the stomach walls. In favor of this assertion is the fact that hunger contractions can be made to subside by rectal feeding.

The eating of indigestible matter temporarily abolishes the contractions. Furthermore, the hunger excitant is more or less periodic and sudden, while changes in the composition of the blood from starvation are more likely to be gradual and continuous. Chemical changes in the blood due to starvation are not very marked; hence it is difficult to make any statement about what they are and what their probable effect is. Nevertheless, this is an interesting notion and one capable of experimental test as soon as knowledge of blood chemistry and physiology of the digestive tract is more advanced.

The fact that stomach contractions have a powerful effect upon the activity of the skeletal muscles has long been recognized. In studies of animal learning, hunger is used to increase overt exploratory activity. The genuinely hungry animal will keep persistently at this activity until its needs are supplied.

Although the stomach contractions excite the organism to activity which may bring it to the source of food, the hunger mechanism is by no means an adequate defense against starvation. These contractions are greatest when an inadequate amount of food is provided, rather than after a long period of fasting. Experiments have shown that the influence subsides after three to five days. Many cases of malnutrition due to intestinal disorders have been reported to exhibit starvation symptoms but to show no accompanying hunger contractions. Certain non-nutritive materials, if taken in sufficient amount, will equilibrate or absorb the majority of chemicals which are acting on the stomach wall. Hence the exciting effect must be the result of a nutritional state which is transitional between starvation and satiety.

As to the acquisition of definite "purposeful" feeding responses we can say little at this time. It may be helpful to point out, however, that in the case of human infants certain types of random movement, having once been successful in bringing about a stomach condition which equilibrates and satisfies the original chemical excitants, may become a fixed and focal part of any ensuing pattern of movement to the same excitants. The sucking and swallowing reflexes probably develop in this way, to say nothing of all later adult elaborations which take place in the task of getting food.