Proof And Probability
For many years firm but not conclusive evidence suggested that lowering the amount of cholesterol in the blood would help prevent heart disease. Populations with high blood cholesterol levels experienced more heart attacks than those with low levels. But this neat correlation was not considered absolute "proof," and rightly not, because other differences between the populations might show a similar correlation but have nothing to do with susceptibility to heart attacks.
The population with more attacks might be mostly blue eyed,
and the other one brown eyed, but it wouldn't necessarily mean that to be blue eyed was to carry a time bomb in your chest. Correlation is not the same as causation! It only tells you where to look. Despite population data and other "correlation" evidence, the only way to obtain scientifically acceptable "proof" of the association between blood cholesterol and heart disease would be to take a large number of persons from the same population, put half of them on a cholesterol lowering regimen, and see if that half developed less heart disease than the rest. This critical test was recently performed in a 7 10 year, $1 50 million study conducted by the National Institutes of Health. It formally proved that lowering blood cholesterol will substantially decrease the chance of a heart attack. But for years before this "proof" was in, many very creditable physicians, including professors at major medical schools, recommended measures aimed at lowering blood cholesterol. They did so on the basis of inferential, or "probable," evidence gained from observations in humans and experiments in animals. Other equally prestigious doctors didn't agree that the evidence was enough to act upon. Until formal proof is established, such matters remain legitimate questions of judgment, which varies from one physician to another, and even between panels of experts. In 1980, for example, the Food and Nutrition Board of the National Research Council was unwilling on the basis of available data to recommend much at all in the way of nutritional changes in the American diet, whereas in the same year and on the same body of data a committee of the American Heart Association advised lifelong adoption of a considerably altered diet. This illustrates our situation concerning many aspects of preventive medicine, including ways to slow down the aging process. Should we wait for "conclusive" evidence which may be years away and too late for some of us? Can we in some instances accept "probable" evidence?
Physicians, patients, and bodies of experts alike should realize that not taking a stand, insisting on waiting until all the evidence is in, is itself a position and a recommendation. Not taking a stand is not really the neutral position it is made out to be. We cannot easily run a $150 million 7 10 year conclusive study on every promising assembly of "probable" evidence about preventing disease and retarding aging, so we must either stay neutral and do nothing or take a stand on the basis of imperfect evidence. Physicians like to pretend, and many have kidded themselves into believing, that whatever they espouse has been "scientifically proved." Nonsense. A great deal of what established medicine recommends with good conscience is not formally "proved the health benefits of exercise, for example: the formal proof on that is not yet in, yet practically all physicians recommend it. And they are right to do so, because the "probable" evidence is excellent. Recommendations about disease prevention and life extension are only as good as the ability of the recommending person to analyze and judge a wide assortment of important but inconclusive evidence. In this book I undertake to explain and rate the evidence, analyze it, judge it, and make specific recommendations. My credentials in relation to age retardation are among the best in the world. In the matter of disease prevention, they are less, but they reflect extensive reading on the subject, plus my experience as a teacher and practitioner at the University of California School of Medicine. By "rating the evidence" J mean stating whether any case in point can be considered to display a very high order of probability , a high order of probability, a moderate order, or less. It is almost certain that a diet super high in nutritive quality but low in calories (the "high/low diet" described in this book) will retard your basic rate of aging, greatly extending your period of youth and middle age; postpone the onset of such late-life diseases as heart disease and cancer; and even lower your overall susceptibility to disease at any age.
