THERE is a wisdom in this; beyond the rules of physic: a man's own observation, what he finds good of, and what he finds hurt of, is the best physic to preserve health. But it is a safer conclusion to say, This agreeth not well with me, therefore, I will not continue it; than this, I find no offence of this, therefore I may use it. For strength of nature in youth, passeth over many excesses, which are owing a man till his age. Discern of the coming on of years, and think not to do the same things still; for age will not be defied. Beware of sudden change, in any great point of diet, and, if necessity enforce it, fit the rest to it. For it is a secret both in nature and state, that it is safer to change many things, than one. Examine thy customs of diet, sleep, exercise, apparel, and the like; and try, in any thing thou shalt judge hurtful, to discontinue it, by little and little; but so, as if thou dost find any inconvenience by the change, thou come back to it again: for it is hard to distinguish that which is generally held good and wholesome, from that which is good particularly, and fit for thine own body. To be free-minded and cheerfully disposed, at hours of meat, and of sleep, and of exercise, is one of the best precepts of long lasting. As for the passions, and studies of the mind; avoid envy, anxious fears; anger fretting inwards; subtle and knotty inquisitions; joys and exhilarations in excess; sadness not communicated. Entertain hopes; mirth rather than joy; variety of delights, rather than surfeit of them; wonder and admiration, and therefore novelties; studies that fill the mind with splendid and illustrious objects, as histories, fables, and contemplations of nature. If you fly physic in health altogether, it will be too strange for your body, when you shall need it. If you make it too familiar, it will work no extraordinary effect, when sickness cometh. I commend rather some diet for certain seasons, than frequent use of physic, except it be grown into a custom. For those diets alter the body more, and trouble it less. Despise no new accident in your body, but ask opinion of it. In sickness, respect health principally; and in health, action. For those that put their bodies to endure in health, may in most sicknesses, which are not very sharp, be cured only with diet, and tendering. Celsus could never have spoken it as a physician, had he not been a wise man withal, when he giveth it for one of the great precepts of health and lasting, that a man do vary, and interchange contraries, but with an inclination to the more benign extreme: use fasting and full eating, but rather full eating; watching and sleep, but rather sleep; sitting and exercise, but rather exercise; and the like. So shall nature be cherished, and yet taught masteries. Physicians are, some of them, so pleasing and conformable to the humor of the patient, as they press not the true cure of the disease; and some other are so regular, in proceeding according to art for the disease, as they respect not sufficiently the condition of the patient. Take one of a middle temper; or if it may not be found in one man, combine two of either sort; and forget not to call as well, the best acquainted with your body, as the best reputed of for his faculty.
There is a wisdom here that goes beyond the rules of medicine. Your own observations of what helps or harms you are the best medicine for preserving health. But it is safer to say, This does not agree with me, so I will stop it. It is less safe to say, This causes me no harm, so I may keep using it. The strength of youth lets many excesses pass unnoticed, but their cost comes due in old age. Recognize that you are growing older, and do not expect to keep doing the same things. Age will not be defied. Beware of sudden, major changes in your diet. If necessity forces such a change, adjust your other habits to suit it. There is a little-known principle in both nature and government: changing many things is safer than changing just one. Examine your habits of eating, sleeping, exercise, clothing, and the like. If you judge any habit harmful, try giving it up gradually. But if the change causes problems, return to it. It is hard to distinguish what is generally considered healthy from what suits your particular body. A relaxed and cheerful mind at meals, at bedtime, and during exercise is among the best rules for long life. As for your emotions and mental pursuits, avoid envy, anxious fears, and anger that eats away inside. Avoid intricate, tangled investigations, excessive joy and excitement, and sadness you share with no one. Encourage hope. Favor good humor over intense joy, and varied pleasures over too much of any one. Welcome wonder and admiration, and therefore new experiences. Pursue studies that fill the mind with splendid and noble subjects, such as histories, fables, and reflections on nature. If you avoid medicine entirely when healthy, your body will find it too unfamiliar when you need it. If you use it too often, it will have no exceptional effect when illness comes. I recommend special diets at certain times rather than frequent medicine, unless taking medicine has already become a habit. Such diets change the body more and disturb it less. Do not dismiss any new symptom in your body. Seek an opinion about it. In sickness, make health your chief concern. In health, make activity your chief concern. Those who train their bodies to endure hardship while healthy can recover from most illnesses through diet and careful nursing alone. This does not apply to very severe illnesses. Celsus could never have offered the following advice as a physician unless he had also been a wise man. He made it a leading rule for health and long life to vary habits and alternate between opposites. But he advised leaning toward the gentler extreme. Alternate fasting with full meals, but favor full meals. Alternate wakefulness with sleep, but favor sleep. Alternate sitting with exercise, but favor exercise, and follow the same principle in other things. This will nurture the body while also training it to meet challenges. Some physicians are so eager to please patients and accommodate their wishes that they fail to insist on proper treatment. Others follow medical rules so rigidly that they give too little attention to the patient's individual condition. Choose a physician who takes a middle course. If you cannot find one, consult two, one of each kind. Remember to consult the physician who knows your body best, as well as the one most respected for medical skill.