Consider two very different cars, let's say a Fiat and a Ferrari. You put a gallon of the same gas in each, rev them up, floor it, and go. Do you expect the same ride from both?
Now consider that same scenario, but instead of putting the same gallon of gas in each, you customize as circumstances warrant. The Fiat, living relatively low on the performance rungs, gets a mundane brand of gasoline. The Ferrari gets the high test that better suits its well-oiled cylinders. Are the rides now the same? What if you switch fuel, and give each engine the preferred fuel of the other?
All of this leads inexorably to the next obvious question: Is a gallon a gallon?
Actually, no it doesn't. In fact, the question is a silly, fatuous non sequitur -- the epitome of nonsense. There is nothing whatsoever in our Fiat vs. Ferrari test drive that raises questions about a standard measure of volume.
In my opinion, all of the accelerating nonsense about calories is just this sort of non sequitur. I'll parse the analogy to make my case, and then tell you why I care about this silliness, and why you should, too.
1) Our bodies are the cars. Just as cars can differ dramatically in everything from handling, to torque, to acceleration, to fuel efficiency, so too do our bodies differ in all the nuances of metabolism. Some of us are natively predisposed to be faster, or stronger, or slower, or weaker. Some of us are highly fuel efficient, and some of us much less so -- although relative fuel efficiency defines us as a species. Just as all cars are cars and need some variation on the standard theme of fuel suitable for cars, so too are all humans human. We need variations on the same basic human fuel, but we burn it across a range of human metabolic idiosyncrasy. We are much the same, and quite different from one another. So: Is a calorie a calorie?
2) Food is the fuel. Not all gasoline is created equal, clearly. At a minimum, as we know from every stop at the gas station, there is regular, plus, and super -- or some other nomenclature for 87, 89, and 92 octane, with the octane rating referring to how much pressure the fuel can withstand before detonation. The various fuels have different performance characteristics based on their qualities. But, of course, you still have to choose the quantity as well -- and put in a gallon, or several, or enough to fill the tank. So, is a calorie a calorie?
3) A measure only measures what it measures. A gallon of fuel is a gallon of fuel. But that, by itself, tells us nothing about the composition of the fuel, or the nature of the engine destined to burn it. There is nothing in the measure of a gallon that precludes the important implications of these two considerations: a gallon of what, being put into what tank, for combustion by what engine? Equally true is that the nature of the fuel and the engine do nothing to alter the standard measure of volume. So, is a calorie a calorie?
Yes, it is. A calorie is a calorie.
Because a calorie, too, is a standard measure -- just of energy, rather than volume. This is something I have written about several times before (see, for instance, here, and here), so I won't belabor it now. Suffice to say that the measure we tend to use, the kilocalorie, is the energy required to raise the temperature of one liter of water one degree Celsius at sea level. If that sounds like an invitation to debate, I'm not getting it. The calorie is every bit as standard a measure as the gallon, the minute, or the mile.
But let's acknowledge that the quality of fuel, the way a minute is spent, and the terrain spanning that mile all matter -- perhaps enormously. The fuel might be pristine or poison. The minute might be bliss, or torment. The mile might be a literal stroll through the park, or straight up Mt. Everest into the teeth of a blizzard. And yet, I don't see these considerations spawning races to redefine minutes or miles. We have always had the sense to know that a standard measure captures only one relevant property. We have never, to my knowledge, failed to allow for the fact that how a minute is spent or where a mile takes us -- matter.
In the case of nutrition specifically, and health in general, we seem inclined to renounce exactly such sense, grant comparable attention to every opinion and cockamamie notion, and in general invoke a whole different set of harebrained rules. In the case of nutrition, if the quality of calories matters, then it must mean that the quantity never did, right?
Why on earth should it mean any such thing? The fact that every one of us has spent both pleasant and unpleasant minutes during our lives has not goaded us to renounce the relevance of that 60-second span. We have long since reconciled ourselves to the idea that both quantity and quality matter.
That -- exactly that -- is true of calories as well. All the rest is sound and fury, signifying nothing, as told by iconoclasts to an overly naive audience. Why are we overly naïve when it comes to nutrition and everything attached to it? My best guess is that desperation breeds gullibility. So many people struggle with diet and weight, it creates a very attractive seller's market for iconoclastic rubbish.
The evidence that the quantity of calories counts, along with the quality, is incontrovertible -- beginning with the laws of thermodynamics first established by Sir Isaac Newton. There is a fixed relationship between matter and energy, bound by the laws of physics. Biological variation is important, but physics is the bedrock on which other sciences, including biology, must stand.
In addition, there are modern studies. Some have shown, quite decisively, that overfeeding of even very high-quality calories leads predictably to weight gain. Others have shown that restricting calories, even if those consumed are junk, leads to weight loss. The authors of such studies do not go on to say that the quality of calories, or variations in human metabolism are irrelevant. They simply say, correctly, that calories count.
Which leads to why I care, and why you should too. Misleading urban legends encourage us to miss out on real opportunity, and/or bog down in boondoggles. As an example, I have long heard -- as you no doubt have -- that more nutritious foods cost more. I kept asking for data, and no one seemed to have any. When my colleagues and I studied the matter ourselves, we found that more nutritious foods sometimes cost more, and sometimes less, and across the full expanse of supermarket choices, there was virtually no price differential between more and less nutritious options. The real problem was that people lacked the skill set to identify the more nutritious choices that didn't cost more. The trouble with this is that the urban legend that more nutritious food always costs more has long been dissuading people from even trying to find it. That's bad.
Similarly, the idea that calories don't count is taking on the status of urban legend. There have been many opinion pieces over recent years posing the seemingly deep, but really pseudo-intellectual question: Is a calorie really a calorie? But now, the idea that a calorie isn't a calorie has become an article of faith. I received a message to one of my LinkedIn groups recently that began with the assertion that "since, of course, a calorie ISN'T a calorie..." and then went on from there. Just as misleading information about food costs can forestall useful efforts to eat better, so can nonsense about calories forestall efforts related to energy balance. Just look out at the vista of modern epidemiology, with obesity and chronic disease rampant, and ask yourself if we can really afford to fritter away more time and opportunity in boondoggle.
There is variation in the human machine, across a greater range than Fiat to Ferrari. There is variation in the quality of human fuel, across a vastly greater expanse than 87 to 92 octane. These things matter.
They do not, however, obviate the reliable definition of the calorie as a standard measure of energy, nor do they invalidate any of the laws of thermodynamics. The calorie is a calorie, and calories do count. Both quality, and quantity, matter.
The race to redefine the calorie has a vociferous group of iconoclasts revving their engines. If you are genuinely convinced that any of these characters is smarter than Sir Isaac Newton, and/or has probed to levels of understanding beneath the bedrock of physics, by all means, wave the checked flag. Otherwise, get out of the way so they don't run you over.