Many of you have doubtless already seen the commentary in the New York Times by my friend and colleague, Dr. David Ludwig (with Mark Friedman, whom I don't know), entitled: "Always Hungry? Here's Why." If you have not read the piece, I commend it to you.
Regarding Dr. Ludwig, he is indeed both colleague and friend -- and I am proud to call him both. He is a prolific, insightful and accomplished researcher -- and one of those rare individuals whose intellect sends out sparks to ignite better thinking by those around him. For whatever my opinion is worth, I consider Dr. Ludwig one of the best in the business of both learning what we need to know about diet and health, and putting it to good use.
Regarding the New York Times piece, and the more scholarly commentary in JAMA on which it is based, I have a number of favorable impressions. The commentary essentially posits that we are not fat because we overeat, but overeat because we are fat -- exploring the inner life of the adipocyte and its interactions with an array of hormones, insulin salient among them -- to make that case. The commentary is thoughtful, well reasoned and provocative. Dr. Ludwig's excellent research, focused on glycemic index and load in particular, is cited for support.
But I am worried that even commentary of this caliber is subject to the law of unintended consequences, which has been the bane of public health nutrition for far too long already. In particular, I searched the text of both the pop culture and scholarly versions of this essay, and in neither case found any of these four words: survival, culture, satiety or synthesis. I think these are crucial considerations, and potentially grave omissions.
On Survival:
Drs. Ludwig and Friedman posit that we overeat because we get fat, but that merely begs the question: Why did we get fat in the first place? They address this to some extent, but fail to emphasize what I think is the essential, and obvious answer: survival. Throughout most of human history, calories were relatively scarce and hard to get, and physical activity was unavoidable. We are adapted to that world. But we have devised a modern world in which physical activity is scarce and hard to get, and calories are unavoidable. Houston, we have a problem.
In a world of relative caloric scarcity and fairly constant demands for physical exertion, appetite for salt, sugar, fat, calories, variety -- all fosters survival. In nature, you eat what you can when you can, and you don't get fat not because you are trying to avoid it, but because survival is challenging and conspires against it. In an unnatural world of constant abundance of tasty calories and labor-saving technology, you behave as you always have -- but wind up with very different results.
You get fat. And then, sure, being fat may propagate the problem in a number of ways -- but the bedrock explanation for overeating is not being fat; that is an obvious chicken-and-egg conundrum. The bedrock explanation for getting fat is: we have made it fun (e.g., tasty food; sedentary recreation) and easy to get fat and hard (e.g., a need for constant restraint; hectic schedules; etc.) to avoid it.
On Culture:
Culture is bigger than any one of us. Cultural variation in behavior and health outcomes tells us rather indelibly, whether we like the message or not, that the basic care and feeding of the human body is highly dependent on actions of the body politic.
The Blue Zones have longer lives, better health and more happiness than the rest of us not because of a preferential focus on calories, or refined carbohydrates -- but rather on living well. When pleasure is derived from strong social connections, there is less need to get it from toaster pastries. When culture normalizes good use of feet, forks and fingers; and encourages attention to sleep, stress mitigation and love -- health and long life result, all around the world.
Our inclination to keep chewing calories into ever smaller bits of academic grist may be the very opposite of what we really need: the big picture. Our culture markets multi-colored marshmallows to our kids, and tells them they are "part of a complete breakfast!" Highly paid advertising executives engineer the angle of gaze on cereal boxes by iconic cartoon characters to influence, maximally and subliminally, the responses of children and adults alike. And we need to ask why are we fat? Come on! Maybe "hypocrisy" should be on my list of missing key words, too. Our culture seems to have no shame of it.
On Satiety:
Satiety refers to a feeling of fullness, and implies something about its duration as well. We have long recognized, all but intuitively, that the satiety attached to diverse foods is highly variable. For instance, we have referred in the vernacular to some foods as "stick to the ribs," meaning they make -- and keep us -- full.
But now, again, welcome our cultural hypocrisy. We invite the likes of Dr. Ludwig to debate the origins of obesity, even as teams of Ph.D.'s work for Big Food companies to engineer foods that maximize the calories it takes to feel full. Michael Moss is only the most recent to tell us this tale; others have before. In a world where functional MRI scans and teams of scientists design foods so that bets that we "can't eat just one" are entirely safe, the relevant question is not why so many of us are fat -- but how on earth any of us manage not to be!
The key issue here is that inattention to satiety invites us to debate the relevance of calories, and carry on as if there is a choice to make between the laws of thermodynamics and the machinations of appetite. Why choose? The quantity of calories figures relevantly into energy balance and the hegemony of thermodynamics, while the quality and character of those calories determine how many it takes to feel full. The prevailing tendency in our culture is to maximize the calories it takes to feel full -- making epidemic obesity little less than a fait accompli. We can reverse engineer this process to astonishingly good effect -- but few in our society have the relevant skills.
On Synthesis:
And finally, the dualistic view advanced here -- calories must be about quantity, or quality; obesity must be cause, or effect -- may obscure a truth that is both more holistic, and more actionable. In other words, what we get in the commentary is another hypothesis, while in my opinion, what we most need is synthesis.
Consider, for instance, the work of another friend and colleague, and another exemplar of the academic method, Dr. Brian Wansink. Dr. Wansink's research has shown that substantial variations in both the quantity and quality of foods consumed can be achieved by influencing such factors as lighting, placement and packaging -- before ever even addressing the composition of the food itself. Instead of a seemingly endless parade of competing hypotheses about what truly matters, why not consider the possibility of a truth that is greater than the sum of its parts: Just about every aspect of modern culture that makes it modern is obesigenic, and if we want to fix the problem, we have to fix it comprehensively.
Calories count, but counting calories is tedious business. And besides, few people are willing to spend their lives hungry when they have the option of fullness and satisfaction. So the answer is to reduce the calories it takes to feel full. That means eating better food, which in turn requires knowing what "better" food is (we do); being able to find, choose and afford it (all possible -- but how much better we could do!); combining better eating with routine physical activity; and shutting down the forces of cultural hypocrisy that invite us to wring our hands about epidemic obesity even while actively propagating it.
Drs. Ludwig and Friedman talk about the research we need. Maybe among it is a study of how a predilection for highlighting our doubts and debates as publicly as possible forestalls any meaningful action based on what we do know. Again, it would be as if your foot catches fire, and you feel compelled to read competing theories about combustion point, flammability, flame retardants, the partial pressure of atmospheric gases, wound care and skin grafting -- before ever you fetch that pail of water. I say: Go for it!
We must, of course, parse and debate, explore and question to advance our understanding -- which is far from complete, and farther still from perfect. But then again -- how perfect does our knowledge of combustion need to be to fetch a pail of water if our foot catches fire? There is a point at which debating the subtleties of what we don't know while failing to act on what we do know may come dangerously close to fiddling while Rome burns.
In other words, as good and erudite as Dr. Ludwig's insights are, maybe the calorie has been sufficiently well chewed already. And maybe endless rumination paves the road to procrastination and ruin.
-fin
Dr. David L. Katz has authored three editions of a nutrition textbook for health care professionals. He is editor-in-chief of the peer-reviewed journal, Childhood Obesity, and President of the American College of Lifestyle Medicine. He was commissioned by Annual Review in Public Health to write the review article, Can We Say What Diet is Best for Health? He is the author of Disease Proof, and most recently, of the epic novel, reVision.