In order for man to succeed in life, God provided him with two means, education and physical activity. Not separately, one for the soul and the other for the body, but for the two together. With these means, man can attain perfection.
-Plato

As the quote implies, physical health and mental acuteness are in no way separate, but depend on each other symbiotically. This may appear puzzling at first, for those unfamiliar with the true, physically-derived nature of the mind. It is easily observed, however, that bodily exertion plays a vital role in the prevention of depression, retention of energy, stability of emotions, and clarity of though. Conversely, this relationship is clearly explained through the realization that the mind depends, in its entirety, on the body for sustenance. In truth, what is commonly called mind is an internal projection of the state of condition of the body.

The fascinating correlation between body and mind becomes less abstract when viewed from the point of everyday experience. The hormaonal effects on mind which come with exercise can be experienced first-hand, for instance. The hormonal changes which physical activity induces can have drug-like effects on the mind (adrenaline rushes and runner's highs are well-known), as well as long-term stabalizing effects on mood. Drug use itself is a useful illustration. Consider the material nature of a drug, whether in pill, shot, or other form: simple chemicals. A pill is such a harmless, inert object when held in the hand. When ingested, however, its power over the mind is easily seen. The connection between physical objects, chemicals, and the mind is easily understood once it is realized that the mind it a physical, chemical system in itself.

It is doubtful that Plato was referring to opiates and amphetamines when he referred to physical activity, though. The Greeks were well aware of the mental benefits of exercise, as well as the mind's condition's influence on the body. Also, your doctor is not lying to you when he says a change in diet will improve your mental health (if particular chemicals alter your mind as drugs, why woulodn't food chemicals do the same?). Remember, your body/mind is made up only of the molecules you ingest, so choose wisely. your body produces its own, natural drugs, level of excercise and type of diet determining which ones.

While the practical benefits of understanding body/mind interaction are numerous, philosophical considerations are also present. What change in brain chemistry is brought about by prayer or meditation? Does belief in God make people happier or more productive? What are long-term effects of physical and mental stress on a person, and shouldn't our society evolve with these effects in mind? And, perhaps most importantly, how do your physical and verbal actions toward another person affect their self-esteem and personal happiness? Love, compassion, and understanding might be the most powerful mind-altering drugs of all (Jesus and Buddha would say so, I think).