05/15/2011 08:41 pm ET Updated Jul 16, 2011

What Do We Really Know About Health?

Knowledge is not power. Where there's a will, there may or may not be a way. And fitness must be made to fit. Some truths are, indeed, self-evident -- others require a bit of cultivation.

In the world of 21st century health promotion, among the more salient and self-evident of truths are these: avoiding tobacco is a good idea; as is eating well; as is being physically active. A repetitive drumbeat of biomedical research has rapped this message for decades, impressing upon anyone paying attention a respect for the hegemony of feet, forks and fingers over our health. We may hold it to be self-evident that feet, forks, and fingers are master levers of medical destiny.

There is a potential tyranny, however, in such self-evident truth. For one thing, we may tend to forget that today's established fact might have been yesterday's raging debate. We did not always know the perils of tobacco. The follies of history suggest that tomorrow's common sense may be incubating in today's heated controversies.

And for another and even greater threat, we tend to believe that any truth widely embraced should portend behavior widely adopted. Would that it were so!

In the world of health promotion, and doubtless many parallel worlds as well, knowledge clearly isn't power. Knowledge may be necessary for power; it may be prerequisite. But a bounty of epidemiologic evidence reveals that it is not sufficient.

We have known for decades about the leverage of feet, forks and fingers -- yet a quarter of us still smoke; three quarters of us are too sedentary; and almost too few of us to bother counting practice any variation on the theme of optimal eating.

This divergence of what we know from what we do is the basis for one of today's more volatile public health debates: to what extent is the pursuit of health a matter of personal responsibility? Since we know it, shouldn't everyone ... just do it? My hope is that a truth we will hold as self-evident tomorrow is germinating in this hot brew today.

That truth? Before we ask people to take responsibility, we must ensure they are empowered. We need both will, and way.

There is, undeniably, a role for personal responsibility in the pursuit of health. No one else can eat well for us; no one else can be physically active on our behalf. At the end of the day, how each of us uses our feet and forks is up to us.

But what is not truly up to us is the environment we encounter each day. It was not up to us to be born into the modern world, rather than the medieval world, or the Stone Age world. The need to work long hours at a desk or in a cubicle; the need to live in a place ill-suited to routine outdoor activity; the need to manage a hectic daily routine, or earn minimum wage may be less matters of choice, more exigencies of modern survival.

Throughout most of human history, calories were relatively scarce and hard to get; food came exclusively from nature; and physical activity was unavoidable. We have devised a modern world in which physical activity is scarce and hard to get; food comes overwhelmingly in bags, boxes, bottles jars, and cans, and calories are all but unavoidable.

Arguments that personal responsibility should simply overcome all of this are in equal measure blind, arrogant and unsubstantiated. They are blind to the realities of epidemiology: an overwhelming majority of Americans, and a fast rising percentage of the global population, eats too much of the wrong foods, is less active than recommended and is prone to obesity and chronic disease as a result.

They are arrogant because they ignore the fact that Homo sapiens are ... creatures, bound by a native habitat, constrained by native traits and tendencies and natural defenses. Homo sapiens have no native defenses against caloric excess or the lure of the couch, because we never needed those in a native habitat devoid of suburban sprawl, and all-you-can-eat buffets.

They are unsubstantiated because there is no evidence of any kind that the current generation of adults, or children, is less endowed with personal responsibility than any prior. We have little cause to think our ancestors had will power we lack, and abundant cause to know they lacked the vending machines and video games we have.

All of which leads us to that germinating truth. Knowledge is not the same as power. Will is not the same as way. We need both. There can be a need for both personal responsibility, and public policy. Health is best pursued along a middle path we have barely begun to pave.

We can, and I believe must, both cultivate a will for health, and pave that more passable way. We can call on ourselves and one another to put our feet and forks to good use, and collectively create better opportunities for doing so.

Some years ago, my colleagues and I developed a physical activity program designed to fit into the nooks and crannies of the school day. ABC for Fitness™ has proven to be a very successful "way" for kids to get the recommended daily dose of recess, without interfering with reading, writing or 'rithmetic.

We now offer the same opportunity for adults. The new A-B-E (Activity Bursts Everywhere) for Fitness® program is freely available to anyone with internet access, and allows you to build a sequence of brief, expertly guided activity bursts into your daily routine in any setting. The evidence is strong that the benefits of routine physical activity are comparable whether the activity is acquired all at once, or throughout the day.

So, here, then, is a new way to get there from here. The will to try it is up to you.

I hope to meet you soon -- walking briskly -- along the middle path where truth prevails, fitness fits and personal responsibility and will for health are empowered by the dedicated efforts of the body pave the way.

Dr. David L. Katz;