This section is from the book "Health Without Medicine. A Treatise On The Laws Of The Human System", by Larkin B. Coles. Also available from Amazon: Philosophy Of Health.
Time for exercise has an important connection with digestion, and is indispensable to health. It is important to the healthy state of body and mind. Bodily health cannot be secured without doe attention to exercise. Persons of sedentary habits, especially, should give particular attention to this subject. Persons of active or laborious habits can make their business subserve the purpose of exercise; while those whose daily task requires little physical exertion, need some other exercise. By such, let this part of the subject be particularly heeded. To illustrate what is meant, take the case of the shoemaker: his business chains him to the bench; it gives him insufficient bodily exercise; he is too much confined.
The shoemaker, then, or the man of similar occupation, should endeavor to have a garden to cultivate, if in the country, because this is one of the very best kinds of employment for exercise; it affords physical motion and exertion: it gives amusement to the mind, and it secures healthful influences from the earth. If this means cannot be secured, then resort should be had to cutting wood, or some other useful exertion; if this cannot be obtained, then he must resort to some artificial exercise; at all events, some kind of brisk and smart exercise should be had early in the morning before breakfast. This gives activity and energy to the body, greatly invigorates the appetite, and exhilarates the mind. After breakfast, he can go to his bench if he please; but he should never put himself to hard work short of about one hour after taking his meal. He may do light work, but should never put himself to severe exertion in any way for about one hour. This rule applies, as also the previous one, to all sedentary habits. It also applies to every meal. In every case of a similar kind, where exercise is taken for recreation, it should be immediately before each meal, and not immediately after it. And as dinner is generally the heaviest meal, one full hour at least should be allowed after finishing it, for the first step towards digestion, i.e., the mixing of the food with the gastric juice.
Now for a reason for this rule; let the dinner be taken for an illustration: why should we rest from much exertion after taking our dinner? And this rule applies with equal force to all classes of persons and all kinds of business; the reason is this: when a meal is to be digested, or, more properly, while the food is being broken up by the gastric juice, which process occupies in the case of a dinner full one hour, the nervous energies of the whole system are drawn into sympathy with the stomach, and made tributary to this part of the digestive process; their aid is needed: this is a law which the Author of nature has established, and it should be obeyed; i.e., nothing should be allowed to interrupt this natural arrangement. But if we allow ourselves to make much bodily or mental exertion during the hour mentioned, we distract this arrangement; because when bodily exertion is made, the nervous energies are required and drawn in that direction, in aid of the muscular powers; or if the mind is made to labor, then the nervous energies are called in that direction. Hence, when body or mind is taxed considerably immediately after eating, the process of digestion is much disturbed and interrupted.
Everybody's experience corroborates the truthfulness of this theory. We know that after a full meal, especially a dinner, there is a disinclination to much bodily action or mental effort; so strong is the draft upon the nervous energy, or nervous fluid, or animal electricity, whichever it may be called, that it is with difficulty we can call it in any other direction. Therefore, to make much exertion of body or mind immediately after a meal, is to violate a law of the animal economy. To attempt hard work, or study, within one hour after eating, will induce in any one, except the most vigorous system, with a cast-iron stomach, derangement in the functions of the digestive organs; the food will not digest so well, and the system will not be as well nourished from the same quantity of food. Hence, the whole system is impaired, its vigor and durability are diminished, and life is shortened.
It is in vain that we contend that nature has no rules -- the Maker of these bodies no laws -- violated law no penalty. It is worse than idle to say, here are A, B, and C, -- they have lived to a great age -- have been robust, and have never observed these rules. The general rule is one thing, and the exceptions make another. These instances appear to be the exceptions to a general rule. But are they really and in all respects exceptions? Because some who have kept their bodies and souls in a gradual steeping of alcoholic liquor have been apparently robust, and have lived to old age, is it proved that alcohol has never done them injury? But while one has lived a long life in violation of law with seeming impunity, a hundred and one, especially of those who have followed sedentary habits, literary men in particular, have gradually ruined their constitutions. Whoever has intelligence enough to know that nature has laws, is in duty bound to obey them, and not run the hazard of laying temptations for disease. And whoever will take the safe side of this matter, will always find it for his good. Even the farmer, in the most driving season of the year, will find obedience to law to be for his interest. Let him conform -- and his men with him -- to the old maxim, "after dinner sit awhile," even one hour, or, what might be better, instead of sitting idle, let all hands do some light matter such as tinkering and preparing tools, and he will find, in the long run, more work accomplished, with less expenditure of strength.
After exercising very lightly for one hour after eating, then let them begin to increase their amount of labor, and keep themselves pound down to work until the time of another meal. This light exercise, immediately after eating, if it be something artificial, i.e., got up simply for exercise, should not only be light, so as not to require real muscular exertion, but it should be something that is adapted to amuse and exhilarate the mind. The state of the mind has much to do with the health of the body, and especially the healthy and free action of the digestive organs. Hence, it is exceedingly important, in all efforts at exercise, that the mind be interested in whatever the hands undertake. Anything that is a piece of drudgery to the imagination, would be of little service to the body.
The fact that the nervous energies are attracted in the direction of the digestive process immediately after a meal, which renders any considerable physical or mental exertion at that time particularly burdensome, is proved true in the conduct of dumb animals. When the ox or the horse has grazed a full meal, he immediately becomes indisposed for exertion or activity. And the same rule should be observed in regard to his labor, that has been recommended for human beings; he should never be forced into hard labor short of one hour after he has eaten his meal. The ferocious animals, when they have taken a full meal, lose for a time their fierceness, and are comparatively harmless. And so it is with man; if it be necessary to ask a favor of a morose or tigerish man, seek an interview immediately after dinner; if a charity is to be solicited from a creature who carries a miser's soul within his encasement of flesh, see him immediately after dinner, At any other time than after a full meal, they would resist, and succeed, probably, in warding off every motive; but while the nervous energies are taxed with the digestive effort, they cannot rouse themselves so well to meet the emergency; they will rather grant the favor asked, than annoy themselves with the effort necessary to repel the invader.