When patients ask me for a diet plan, I respond with a quiz: “Which is better for you, broccoli or cheeseburgers? How about strawberries or chocolate cake?” It doesn't take a genius to get the point. We all know what healthy food is. The problem isn't our knowledge base; the problem is that bad food tastes better than good food, and we don't have the will power to choose what we know is good for us. A diet plan is typically a waste of paper.

It's the same with exercise. Everybody knows that when they use a riding lawn mower they are making a bad choice. Ditto the leaf blower, the golf cart, the escalator and the moving sidewalk. But the situation with exercise is not quite so bleak as with eating. Exercise, for most people, in one form or another, can be fun. Broccoli is never fun. What our patients need from us is motivation, inspiration, nagging and a clear goal. We've made a difference with smoking; we can probably make a difference with exercise.

The problem is that patients expect a physician to talk to them about numbers. We've created that expectation, and we should be proud of ourselves. Numbers drive research; numbers guide therapy; numbers shock, or reassure; numbers keep score; numbers motivate. When your patients ask for a weight goal, you can provide one. Same with blood pressure, cholesterol, glucose and many others.

But when a patient asks, “Doc, am I getting enough exercise?” what do you say? You can take an exercise history if you have the time to waste, but that's about as reliable as a diet history. We all have an astounding propensity to fool ourselves. With weight you have a number; what do you have for exercise?

We have had an answer to that question for a long time, but no one has yet translated it into the practice of medicine. If you can exercise at the 10 MET level (1 metabolic equivalent of task equals 1 ml/kg/minute of oxygen uptake and corresponds to sitting quietly on the couch with a beer in one hand and the television remote in the other), your risk of death from all causes is much less than the risk for someone who can't. It's like blood pressure. Lower is better, higher is worse, but 140/90 has served us well. With exercise, 13 METs is a little better than 10, and 6 METs is a whole lot worse. But 10 METs is good enough.

Unfortunately, we can't get MET scores easily. You can do it in an exercise laboratory, but that doesn't help us. Fortunately, there is a well-studied test that will produce a useful number: the timed one-mile walk. A few years ago, the Governor's Fitness Council of Kansas established the one-mile walk as the fitness test for Kansas adults. Since then, the Kansas Medical Society and the Kansas Academy of Family Physicians have made it a new “vital sign” for primary care physicians.

You want a number? Fourteen minutes. Anyone who can walk a mile in 14 minutes is getting enough exercise. This doesn't correspond exactly to 10 METs, because that is a more complicated calculation involving weight, sex and pulse rate in addition to the mile walk time. But it's close enough. If you want to be more precise, go to http://healthykansas.org/whats_your_mile.aspx, take the test and see where you rank. See also http://www.iliffbasictraining.com/pdf/METs_and_Me.pdf.

The medical profession has known for years that fitness is correlated with health. Now we know that it is more closely correlated than any other single factor. It is a wonder, and a shame, that we have not figured out a way to track a simple fitness vital sign before now. Better late than never.