Fathoming the Calorie

Why both the quality and quantity of calories count.

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I have some trouble fathoming our constant questioning of the calorie: Is a calorie really a calorie? Do calories really count? These and related questions have been queued up of late, repeatedly, in such rarefied terrain as National Public Radio and the New York Times.

Eat + Run -- David Katz
David Katz

After all, a calorie is a precise and specific unit of energy, or heat. Namely, it is the heat required to raise the temperature of 1 cubic centimeter of water at sea level 1 degree Celsius. The measure we more routinely apply to food, the kilocalorie, is exactly 1,000 times as much. This is not up for debate, yet we seem bogged down in debating it—which is what I can't fathom.

We don't, to my knowledge, challenge the fathom in a similar manner: Is a fathom really a fathom? Some fish and vessels can descend to great depths, others can't. But we seem to recognize that this is about differences in ships and vessels, not fathoms, and that debating the fathom—used to measure the depth of water—per se, would not help us probe the depths of anything new or worthwhile. We don't ever seem to ask: Is 20,000 leagues under the sea REALLY 20,000 leagues? A league, presumably, is a league—and we deal with that. I have continual difficulty fathoming why we put calories in a league of their own.

Perhaps the answer is all around. Epidemic obesity is all the evidence we need that our relationship with the calorie has changed radically in modern times. For all of prior human history, the calorie was that precious thing we needed and had trouble getting in adequate supply. We loved the calorie!

Now the calorie is the thing we get too much of and can't seem to avoid. This would seem a basis for resentment, if not disgust. And perhaps this relatively sudden change in our relationship with the calorie compels us to wonder if the calorie itself has changed.

There's also the fact that the calorie seems capricious. Any two of us may eat comparable numbers of them, and one of us gets fat, while the other stays thin. Something fishy is surely going on there!

And then there's the tendency for desperation to breed gullibility—or at least wishful thinking. Weight control, individually and collectively, is hard, and we share a lot of frustration on that score. It might alleviate it a bit to know the calorie was playing tricks on us—that the source of such woes lies not with ourselves, but our stars after all. The calorie as chameleon gives us something to blame.

But the calorie is a unit of measurement, specific and precise, and that unit has not changed. Nor have its implications.

The quantity of calories we consume matters and it's the principal determinant of what we wind up weighing. The relationship between energy and matter is fixed well above the pay grade of New Age nutrition writers. The evidence that quantity matters is clear, consistent, and in my view, irrefutable. Fed an excess of calories, even if mostly from high-quality protein, people gain weight. Assigned to a calorie deficit, people lose weight—even if the calories are mostly from Twinkies. Calories count.

But of course, quality matters too, and it matters on both sides of the energy-balance equation.

Calories go out in three ways: we burn them to survive (resting energy expenditure); we burn them to work (physical exertion); and we waste them (thermogenesis or heat loss). The quality of the fuel we consume can affect both resting energy expenditure, and thermogenesis. Is this surprising? Not at all. We can make fire with wood, or coal; coal burns hotter. Protein, fats, and low-glycemic foods seem to burn a bit "hotter" than simple and refined carbohydrates, a fact corroborated by a recent study in the Journal of the American Medical Association.

Quality matters considerably more, in my opinion, to the calories that come in. We all know the food industry's most famous threat: "betcha' can't eat just one!" Of course, it wasn't intended as a threat, but in an age of epidemic obesity, isn't it exactly that?

Foods can, indeed, be processed into virtual irresistibility based on detailed studies of brain function, imaging of the human appetite center in the hypothalamus. And they can be processed into marvelously efficient calorie delivery systems: energy dense, nutrient dilute, low in volume. The modern food industry is highly adept at maximizing the number of calories it takes to feel full—with predictable benefits to those holding company shares, and predictable detriments to the rest of us left holding the bag of chips.

Wholesome, nutritious foods have the opposite effect. Among their many virtues, they minimize the number of calories it takes to feel full, due to many attributes, among them: high volume, high fiber, low-glycemic index/load, nutrient density, energy dilution, flavor simplicity, etc.

So the quality of calories we consume can affect the quantity. This should be welcome news in our ongoing struggles with portion control. If all sources of calories felt the same, the only way to shrink our portions would be to eat less than we now do—presumably less than we want—and to be hungry all the time. Making higher quality food choices offers us means to feel full on fewer calories, and to get thin without feeling hungry.

The notion that we are apt to overeat some foods and not others (ever heard of an apple binge?) is little less than intuitive. The notion that the source of calories can affect energy expenditure may be less so, but needn't be. We do all know that coal burns hotter than wood. We don't, as a result, tend to ask: Is a degree really a degree?

But let's be sure to keep something else in mind: Even though coal burns hotter than wood, a great, big wood bonfire will generate a whole lot more heat than a few coals in a hibachi. A big fire generates more heat than a small fire, and that effect is apt to trump any differences in what is being burned. Both quantity and quality can matter—this isn't really rocket science.

Why do I care, and why should you? Because there are no good answers to silly questions. The longer we keep asking such things as—Is the calorie really a calorie? Do calories really count?—the more personal and societal resources we divert from the questions that matter: How can we fill up on fewer calories? What tools, skills, policies, programs, and practices can best help us lose weight and find health, in a modern, obesogenic environment? Questions about the nature of the calorie forestall the progress we need—and I'm always tempted to think the producers of calories are behind them.

While "waitin' on the world to change," here is my advice to you:

• To control weight, you must control calories—quantity matters. Period!

• The best way to control quantity is by improving quality. One of the many virtues of wholesome foods is that they help us fill up on fewer calories. Eat lots of simple foods that are close to nature.

• More of the right kinds of fat can be helpful. Monounsaturated and polyunsaturated fats are generally good for health and may help with portion control in the right context. An example of that context is the Mediterranean diet.

• Protein is satiating. Up to a point, more high-quality protein can be helpful. Think lentils, beans, meats, fish, eggs.

• Lower glycemic load can be helpful. This does not require cutting carbs indiscriminately, but it does mean avoiding or limiting foods made with refined starches and added sugars.

• Foods can be high in calories, and still help control total calorie intake—if they are rich in nutrients, and help confer a lasting feeling of fullness. We have such evidence for walnuts and almonds.

• While the source of calories may influence how many are burned, this is a trivial effect compared to that of…exercise! If you really want to burn more calories, you will get far more out of changing what you do with your feet than by changing what's at the end of your fork.

All of these tips are as much about finding health as losing weight, so they are advisable whether or not you have weight to lose. And, as noted, no rocket science is involved.

Speaking of which, the definition of the calorie and the relationship between energy and matter (which includes body fat) are rooted in laws of thermodynamics. Anyone inclined to debate the meaning or significance of the calorie, in other words, is going toe to toe with Sir Isaac Newton. And while some of those opining on the topic are quite intelligent, I think it's safe to say that if they go up against Sir Isaac…they are out of their depth.

Hungry for more? Write to eatandrun@usnews.com 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.