Within the last generation,the following beliefs, for example ,have been widely held:since acne is associated with
oily skin,avoiding oily foods like chocolate and potato chips result in improvement.Since bones my
become brittle in old age through  loss of calcium ( a condition called osteoporosis),a dict high
in calcium prevents brittleness.Since uclers are exacerbated by "strong" substances such as coffee
and alcohol,a bland diet hastens recovery.

    Such beliefs are arrived at through analogy rather than through investigation.Oily food
does not necessarily bear any relation to oily skin. Calcium in the diet is not neccessarily used for
reminralizing bone.Foods that look bland,feel bland,and taste bland are not neccessarily bland
in physiological action.In fact,diet is no longer considered a crucial factor in one or ulcers

    Trial an error has,on the other hand,produced popular remindies that really do work,although
it has taken science to elucidate the reasons.Butter milk and yokurt were used to treat thrush (
now call oral candidiasis), a fungus infection of the mouth,before the invention of fungicides.

Fresh limes were used to treat scurry in sailers,as cod liver oil was used to treat rickets in
children,before science has stumbled upon vitamins or understood deficiency disease.Generations of
people sipped warm milk at bedtime to make them sleepy without having an accurate idea of how the
remedy worked.