The answer, from The Code of Jewish Law (chpt 32, law 3), may surprise you: "Most disease suffered by man comes from, and from none other than, bad foods, or from filling his belly even with good foods." Note the strong tenor of the assertion. The basis for this ruling comes from Maimonides who stated (De'ot 4, 15), "Most illnesses that afflict man are caused by harmful foods or by overeating, even of healthful foods."
In other words, illness comes from what a person puts into his mouth.
As simple as this sounds, if you think Western culture believes it, think again:
Most people, including most doctors, believe germs cause sickness. This is in direct contradiction to what the Code of Jewish Law asserts, namely that food is the main problem, yet medicine prefers germ theory. This has exceptionally significant ramifications, for if intake of food is the real problem, it follows that a proper dietary regimen could cure or reverse the problem, whereas the germ theory of disease suggests an entirely different approach, in fact one that leaves the bad food habits in place!
In fact, medicine today totally denies the Jewish Law or its implications regarding the healing of illness or seeking cures.
People who are sick, who then visit a doctor who prescribes a pill or a shot, who then put that medicine into their bodies - do so without realizing this "food" they take into them is unnatural and cannot be considered "good", yet the doctor pushes the drug, or the patient swallows the pill, without thinking twice. Depending on the diagnosis, this "treatment" could be an occasional one, or, with degenerative disease, more likely a lifelong "diet".
People who are sick, who then visit a doctor who prescribes a pill or a shot, who then put that medicine into their bodies - do so without realizing this "food" they take into them is unnatural and cannot be considered "good", yet the doctor pushes the drug, or the patient swallows the pill, without thinking twice. Depending on the diagnosis, this "treatment" could be an occasional one, or, with degenerative disease, more likely a lifelong "diet".
For the last 100 years, or so, conventional medicine rejected the wisdom of Maimonides. There were doctors in America before that who, in fact, did follow the wisdom of Maimonides, even if they never knew of this sage. To their credit, they derived the knowledge on their own.
Dr. J.H. Tilden, a doctor who practiced medicine for more than 70 years, and lived until the age of 91, wrote in 1921, "The commonest cause of disease is, first, last, and all the time, overindulgence of appetites and passions". Notice how forcefully he states what the Jewish Code of Law also emphatically asserts.
In the late 1800's Louis Pasteur promoted the germ theory of disease. In contrast, Antoine Beauchamp, his contemporary, said, "The primary cause of disease is in us, always in us". In other words, the primary problem was the milieu, the biological terrain. That germs take advantage of this situation is a secondary aspect of the disease.
Whatever the historical reasons, Pasteur's viewpoint overshadowed Beauchamp's and became the holy grail of medical perspective in the West. It prevails until today. Medical education never even broaches a view other than what the establishment prescribes. In fact, the medical curriculum in a U.S. medical school never includes a course in nutrition! Moreover, any attempt to move away from the prevalent viewpoin, to provide therapy based on other premises, immediately draws intense retribution by the powers that be, thus discouraging "unconventional" or alternative medical practice.
Contrast the approach of today's doctor with that of Dr. Tilden, who says:
"As a refutation of the necessity for all the so-called remedies carried into the sick-room - surgery, drugs, prescriptions, vaccination, serum injections; faith, suggestion, and mind cures; the laying on of hands, and every other device known and used as remedial - I offer my simple methods; namely, that of taking nothing into the sick-room, and of doing nothing that can be likened to the modern conception of healing. My methods are devoid of any suggestion of mysticism or supernaturalism, and are not above the understanding of the most commonplace mind, unless its simplicity appears uncanny to distorted understandings.
"I go into the sick-room without a so-called remedy, and, what is best of all, without the need of one. There is no faith cure offered; there is no hocuspocus, legerdemain, nor play on the superstition or credulity of the patient. There is nothing resorted to which may give the impression that unusual or supernatural power is to be used.
"After getting the history of the case, I explain how the patient happened to get sick, how his life differs from nature's requirements, and how he may get well. No drugs, no manipulations - nothing but keep still and don't build disease by foolish acts of mind or body!
"When cause is known, the remedy will be self-suggested to the most commonplace mind. This being as fundamental as truth always is … ." [From his book: Impaired Health: Its Cause and Cure.]
As I said, Dr. Tilden arrived at his understanding of medical disease from pure, rational thought. Let's listen in on some of his wisdom:
"There is no question about the necessary and beneficial action of the bacteria that are in us and about us all the time. The germs that infest our bodies, our food, our atmosphere, our soil, are necessary to our existence. If they were not, they would not be there. Nature never stultifies herself; there is a reason for everything, and that reason is backed by the logic of the Absolute.
"The weakest point in modern medical science is its teachings on bacteriology. It teaches that germs cause disease. If that could be proved, it would establish demonology [as if Hashem acts as a demon], and chaos would reign supreme."
Why germs are necessary we can answer another time. But for now, it should be apparent that germ theory of disease survives not because it's the correct view, but in spite of it.