Our weight, of course, is substantially influenced by our behaviors and choices. I have argued for years, against a backdrop of exotic theories, genetic discoveries, and snake-oil hucksterism, that weight represents energy balance, and is thus overwhelmingly influenced by calories in and calories out. I have made the case along the way that yes, a calorie is a calorie.
But I immediately append something I know abundantly from my clinical experience: Two people can eat about the same, and exercise about the same, and one gets fat and the other stays thin. This absolutely does happen; it is the truth. It's not fair, but who ever told us life would be? Bad stuff does at times happen to thin people, too, and that isn't necessarily fair either.
We don't know all the reasons for accelerated weight gain, or weight loss resistance, but we do know some, and they are the usual suspects. There are important gene variants, to some extent associated with ethnic variation, that influence metabolic rate. There are marked differences in resting energy expenditure, with some individuals, and some whole populations such as the Pima Indians, and the Samoans, noteworthy for extreme "fuel efficiency." Fuel efficiency fostered survival when calories were scarce and physical activity unavoidable; in modern context, it fosters obesity and its sequelae.
We are also learning more, almost every day it seems, about the important influence of our resident bacteria on our weight, as well as our overall health. Variations in gut microbes can substantially alter the fate of the calories we take in, and our propensity for weight gain.
Note that none of this, nor any other exotic theory such as the potential for viruses to cause obesity, alters the fundamental importance of energy balance. If person A has a lower resting energy expenditure than person B, it means that, all things being equal, person A will gain weight more readily and from fewer calories. But that simply indicates that all things shouldn't be equal; person A needs fewer calories. There is inter-individual variation in the equilibrium point for energy balance, where calories in match calories out; but there is such an equilibrium point for us all, and when we find it and honor it, our weight is stable. We need to accept this and deal with it, just as we deal with all other inter-individual variation. Variation in the size of our feet requires corresponding variation in our selection of shoes.
Weight is powerfully influenced, but not directly determined, by our behavioral choices. Some people, making all the right choices, will be heavier than others making the same -- or even less good --choices. And people making good lifestyle choices, including routine exercise, are apt to be fit even if they remain somewhat fat, and will be far better off than those who are either fat or thin, but unfit.
As we foray ever further into an age of incentives and disincentives to nudge people toward better health and lower disease-care costs, it becomes urgently timely to acknowledge that weight is not a behavior. Body mass index is often included among the metrics considered for the application of such nudges in health promotion programming. I think that's wrong. What if two people commit just the same efforts to improving their diets and physical activity, but one loses weight more readily than the other -- is there any rationale for a different application of rewards or penalties? In my view, if someone is relatively resistant to weight loss and is then penalized financially for this "handicap," it is the literal addition of insult to injury (or vice versa).
The causes of epidemic obesity are all around us. We don't want to get carried away with invoking genes or resting metabolic rate to explain obesity at the population level. A half century ago, human beings were the same as they are now; our genes, and metabolisms, were all but identical then as now. Yet rates of obesity are staggeringly different. You can't account for a change in Y with an X that has been constant; if X explains a change in Y, it must be because X has also changed. The changes that account for obesity in the modern world reside in the modern world, not in the relative constancy of human physiology.
But human physiology absolutely does account for variations among us. All members of a common species, we Homo sapiens are more alike than different; but we can be pretty different just the same. Some of us, for instance, are white and some are black. Mostly that is a trivial difference, skin deep. But skin pigment is just the veneer over a compelling tale of survival.
Once, we were all black. But then the great human diaspora expanded our habitat into areas where sunlight was a less abundant resource. Black skin made ample vitamin D in the tropics, but not so in the northern reaches of the temperate zone. So a mutation resulting in fair skin that also happened to confer an ability to make more vitamin D with less sunlight provided a survival advantage -- and all of us here today without our native skin pigment are progeny of that original mutation.
In just the same way, different experiences in different parts of the world favored genetic mutations selectively, resulting in greater or lesser energy efficiency, and other variations in metabolism influencing the propensity to gain, retain, or lose weight. Clearly almost all of us are vulnerable to the obesigenic influences of the modern world, but some of us are far more vulnerable than others. All of us can lose weight when calories in are less than calories out, but it takes very differing efforts for some of us than for others to get there from here.
A half century ago, more or less, obesity was rare. That's not because people had different genes then. It's not because there were better people, with more self-discipline, back in those good old days. It's because a vast array of obesigenic changes have populated the world around us in the past five decades.
Ideally, this would change, and we would devise a modern world that cultivates our health and weight control, rather than conspiring against them. Collectively, we can make that happen -- and I believe we will -- eventually. But it's a slow process; don't hold your breath.
In the interim, it takes skills to be lean and healthy. Those skills can be acquired, and they can do the job.
But even with the consistent application of the same skill set, weights will vary. Weight is only partially determined by factors under our control. As we look around and size one another up, we have to stop thinking that variation in size means variation in effort. Belts and bathroom scales do not measure effort, resolve or determination, let alone anything remotely like human worth.
This is an exciting week for me, with the release of my new book, Disease-Proof. Honestly, I think it's a very good book; and I also think it's very important that it is a totally honest book. It's honest about the incredible power of lifestyle choices to reshape our bodies and our health. It's honest about what it takes to get there from here. I hope, and believe, that we have all had enough of false promises and magical thinking, and are ready to apply the practical magic of skill-power to ourselves and our families. Disease-Proof is a delivery vehicle for just that skill-power.
But since Disease-Proof emphasizes the transformational power of our behavioral choices over health and weight, it seems an important time to note -- as I do from every podium I visit -- that weight is neither a behavior, nor a choice. Nobody wakes up and decides what to weigh.
We do indeed have stunning potential control over our health, and should make better use of it. Our feet and forks are, or should be, the master levers of medical destiny. But even the best application of skill-power will not turn weight into a behavior. Weight is not a choice, and we should all choose to recognize that.
Disease-Proof is available at bookstores nationwide as of 9/26/13, and at:
Dr. David L. Katz; http://www.davidkatzmd.com/
Follow David Katz, M.D. on Twitter: www.twitter.com/DrDavidKatz