Calorie counts, and the very meaning of "calorie," have been recurrent themes in both the medical literature and the popular press of late. Most recently, studies have suggested that calorie counts on menus seemingly do, and don't, help reduce calories consumed.
Closely related to the question of whether it helps to know calorie counts is whether all calories are created equal. Or, in the form of the question that has captured the popular imagination: Is a calorie really a calorie?
In my opinion, this question is abjectly silly no matter how you answer it. It's a silly question whether you think the answer is yes or no. Because of course the answer is both yes and no.
[Read: Accounting for Calories.]
Consider asking, for instance: Is a mile really a mile? This is exactly the same, silly kind of question. A mile is, irrefutably, a mile: 5,280 feet. If it were otherwise, it would not be a mile. In just that way, a calorie (kilocalorie, actually) is exactly the energy required to raise the temperature of one liter of water one degree Celsius at sea level. If it is any other quantity of energy, it is not a calorie.
But just as certainly, a mile climbed up the steeps of the Himalayas will not be experienced at all like a mile strolled through Hyde Park. The distance is the same – but the experience is totally different. This is so obvious that to make a point of it seems almost to suggest subterfuge and even hucksterism. When someone pretends they are rendering an epiphany in the place of the self-evident, they generally have a bridge to sell you. Step away from your credit card, fast.
Of course a mile is a mile. That's important, because we rely on the consistency of that measure to gauge time and distance – just as we rely on the quantitatively consistent nature of calories to inform our considerations of energy balance.
But in both cases, and just as obviously, other factors matter, too – we don't need any epiphanies-on-sale to discern this. We know it will take longer to climb a mile of steps than to walk a mile down a level lane. The qualities of miles vary.
Calories are just the same. A fixed number of walnut calories and a fixed number of Ding Dong calories are very different experiences in every way that matters. Simple, wholesome, nutrient-dense foods tend to help fill us up and keep us full. They don't tend to send a surge of sugar into our bloodstream and spike our blood insulin. Highly processed, energy-dense but nutrient-poor foods tend to engender just such harmful responses.
[Read: The Myth of Healthy Processed Food.]
Do we really need a notoriety-seeking iconoclast and feigned revelations to point out that it's easier to overeat chips or donuts than chickpeas or dates? Did anyone with a remnant of common sense really think the metabolic fate of isocaloric quantities of jellybeans and adzuki beans would be the same? Of course the qualities of calories, like the qualities of miles, matter.
When we consider the question about the constancy of calories in suitable context, the answer quite readily becomes: duh! Of course calories are quantitatively the same; of course calories are qualitatively different.
This leads to another question: Why do I care? And in particular, why do I care enough to rant repeatedly on the topic?
Because we never get a productive answer to a misguided question. Because unproductive answers to the wrong questions kill progress. And because I hate watching progress die. It is exactly the kind of distraction that forestalls public health progress to debate the quantitative nature of a calorie. When we ask, Is a calorie a calorie?, it invites at least some of us to infer it no longer matters how many we consume. That's wrong – it matters. It always has and always will.
And I care because there is the alternative of asking good questions, generating meaningful answers and making real progress. We have abundant cause to acknowledge that both the quantity and quality of calories matter and that each influences the other. We need only do so to generate a constructive question: How do we effectively address both?
In my opinion, there is a straight line of established evidence and simple logic that leads reliably to a robust answer to this question, and we can get there point by point.
Point 1: Of course calories count, and it remains true now as ever that if we take in more than we burn up, we gain weight. We can gain weight eating a lot of good calories; we can lose weight eating few bad ones.
Point 2: Of course all calories are not created equal, and the character of some foods fosters overeating while the character of other foods helps defend against it. No one ever said about heads of romaine lettuce: Betcha' can't eat just one!
Point 3: Many processed foods are actually engineered to maximize the number of calories it takes to feel full.
Point 4: People don't eat to fill a calorie quota; we eat to feel satisfied. So the quantity of calories we take in will vary with how the nature of our food choices influences the number of calories consumed before reaching that feeling of satisfied fullness, or satiety.
Point 5: The number of calories it takes to feel satisfied (i.e., achieve satiety) varies with the properties of food. Among the factors known to influence satiety are glycemic load, volume, water content, fiber content, protein quality and quantity, energy density, flavor variety, texture and even color – to name a few.
[Read: A Tale of Two Fibers.]
Point 6: Even if calorie counts on menus do help reduce calorie intake now, they may not do so over time if less calories now means more hunger in an hour. An exclusive focus on quantity is apt to be a short-term fix to a long-term problem.
Point 7: Among the many virtues of highly nutritious foods is that they tend to help fill us up on fewer calories. Controlling the quantity of calories we ingest matters – but the best way to do it without going hungry all the time is to improve the quality of those calories.
If these are some of the available pearls, what would be the string? Well, we could combine calorie counts with a measure of overall nutritional quality that incorporates all of the factors known to influence satiety. Like calories, overall nutritional quality can be expressed as a single number. I say this with certainty, having led the development of a nutritional quality index that does exactly that, using a scale from 1 to 100: the higher the number, the more nutritious the food. There is thus the opportunity to gauge both the quantity and quality of calories in one fell swoop and at a glance.
Can anyone think that 2000 calories per day of nothing but Twinkies is equivalent in any way that matters to the same 2000 calories of a traditional Mediterranean diet in all its vitalizing glory? On the other hand, does anyone doubt that the same vitalizing Mediterranean diet can make you fat if you only need 2000 calories per day of it, but instead consume 4000 calories? And of course, once it does start making you fat, the ill effect of obesity may obviate partly or entirely the erstwhile benefits of an otherwise salutary diet.
Of course both the quality and quantity of calories matter. The only response assertions about all calories not being equal in all ways should invite is: duh! We knew that all along.
Alas, the response such assertions now invite is the quagmire of point and iconoclastic counterpoint on endless parade. It is past time to get beyond this pointless squabble – and focus instead on connecting the dots.
Hungry for more? Write to firstname.lastname@example.org with your questions, concerns, and feedback.
David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.