All About Calories, Part 1: Do Calories Count?

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About calories

If you really want to start a catfight in the Paleo world, just raise the topic of calories. Is calories in, calories out a load of baloney, or is it the only legitimate way to lose weight? Do you need to count calories for weight loss? Does a ketogenic diet work because it automatically restricts calories, or because it provides some special metabolic adaptation?

As usual, the answer is complicated. And if we try to oversimplify it for the sake of a snappy catchphrase, we’re just making it harder to get to the ultimate goal: better health. So instead of getting caught up in black-and-white thinking about how calories either “count” or “don’t count,” consider that there are really two different arguments going on here:

  • Argument 1: By the first law of thermodynamics, energy cannot be created or destroyed. Weight gain or loss physically must depend on a calorie surplus or deficit. Change in weight = calories in – calories out.
  • Argument 2: Counting calories and increasing exercise (“eat less, move more”) is the best/only way to achieve a calorie deficit and thus lose weight.

Agreeing with one of these two statements does not mean that you agree with the other. You can completely accept the calories-in/calories-out theory, but still think that counting calories isn’t the best way to get there. Alternately, you can consider calories-in/calories-out to be incomplete or even incorrect, but still think that counting calories has some value as part of the big picture.

As it turns out, that’s exactly what happens, and that’s probably why very intelligent people disagree so strongly on the calorie issue. Argument 1 seems to be true, in a certain very limited sense. But Argument 2, the “eat less, move more” prescription, is so oversimplified that it’s useless: it doesn’t even account for all the ways “calories in” and “calories out” can change. So the researcher who stubbornly insists that “calories count” is right, and the frustrated ex-dieter who couldn’t lose weight on 1,200 calories a day is also right. Calories are technically “true,” but human nutrition is so complicated that they just aren’t very useful.

Calories and the Laws of Physics

Let’s start the foray into the science of calories by taking a good hard look at Argument #1, the claim that by the laws of physics, a calorie deficit is the only way to lose weight. This is the line you’ll hear endlessly repeated by obesity researchers and diet experts ‘round the world: “weight loss depends on a calorie deficit.” It’s called the Calories-In/Calories-Out hypothesis, or CICO for short.

The basic idea goes like this: by the physical laws that rule the universe as we know it, energy can’t be created or destroyed. It can only be transformed from one form to another. Calories are one unit of energy (if you want to get really precise, one dietary calorie is the amount of energy needed to raise one kilogram of water one degree Celsius). When you eat food, those calories either get used to do something (move your body around, maintain your body temperature, keep your heart pumping…), or stored as fat. No matter whether they come from protein, fat, or carbs, they must be either used or stored. They cannot magically disappear on the trail of the unicorns, or evaporate into thin air, or vanish at the full moon. If you’re gaining fat, it’s because you ate some calories and they got stored as fat. If you’re losing fat, it’s because some of those calories are coming out of storage and getting used for fuel.

This is usually delivered in that familiar tone of “Science says this, and that’s final” – with the implication that if you don’t believe it, you’re just being superstitious or unreasonable. But then again, we’ve also heard “saturated fat is bad for you” delivered in exactly the same tone. So does the CICO hypothesis actually deserve so much confidence?

Calories: The Other Side of the Story

The main argument otherwise isn’t that calories are a lie, or somehow “false.” It’s that the typical story about “calories in, calories out” doesn’t account for how we use those calories, or why we’re driven to overeat calories in the first place.

Think of it this way: imagine your body is a train, where the people getting on are calories in, and the people getting off are calories out. So the more crowded the train, the more weight you’ve gained. Now imagine that one day, the train is really packed. You might turn to your friend and ask, “why is the train so crowded?” And if your friend is an annoying smart-aleck, he might answer, “because more people got on than got off.”

Everyone understands that that’s a ridiculous answer, and that’s not what you were asking for at all. You were probably expecting to hear something like “because it’s rush hour,” or something else that explains why more people got on than got off. But that’s what the CICO hypothesis does. Why did you gain weight? Because calories in exceeded calories out. This is technically true, but the question remains: what caused calories in to exceed calories out? It’s not nearly as simple as “you ate too much and/or exercised too little,” because there’s a lot more to the “calories in” than food, and a lot more to the “calories out” than exercise.

In other words, the insulin hypothesis (blaming excess carbohydrates for weight gain), and the food reward hypothesis (blaming addictive processed foods), and the lean-tissue hypothesis (blaming nutrient deficiency) all start from the premise that calories count. They just also argue that it’s a lot more complicated than that.

For example, take a look at this. It’s an explanation of the insulin hypothesis from Gary Taubes, one of its biggest champions. But even in this explanation, carbs don’t create fat out of nowhere. Excess carbohydrates raise the levels of a hormone called insulin, which directs calories away from the organs. Organs are the biggest calorie consumers in the body, so anything that stops calories from getting to your brain or liver is seriously reducing the number of calories out. With nowhere else to go, those calories get stored as fat instead. The question isn’t whether calories “count” or “don’t count;” it’s what causes them to be stored instead of used.

To put it in terms of the train image above, insulin would be something like a nasty conductor who prevents anyone from ever getting off the train.  What Taubes is saying is that we need to find this one conductor and get rid of him, instead of focusing on the people – people who would like to get off the train, if only they were allowed.

There are a lot of problems with this idea – to start with, the number of perfectly healthy traditional societies who ate a lot of carbs and yet did not struggle with obesity. It’s not at all clear that the insulin hypothesis is actually useful for explaining what goes on in people who aren’t already diabetic. There’s probably no reason why healthy people should avoid carbohydrates, especially not if they exercise regularly. But for the purposes of this article, what really matters are the claims about calories.

Notice that the chain of events above does not include a step where insulin or carbohydrates manufacture fat out of thin air. This person is still gaining weight because they are storing calories as fat. The laws of physics are not violated. Calories in (food) still get either stored as fat or used for energy; the difference in this case is just that the person is storing more, and using fewer of those calories.

Calories: It’s Complicated

The take-home from the insulin hypothesis is that calories technically “count,” but what your body does with those calories counts more. And that was just the tip of the iceberg: take a look at some of the many other reasons why both the “calories in” and the “calories out” side of the equation are much more complicated than they first appear.

“Calories in” is not just the number on the Nutrition Facts panel. Like any other nutrient, the number of calories you actually get from your food depends on how many you absorb, not how many you put in your mouth. And that’s influenced by…

  • Energy needed for digestion of the food: protein requires more energy to digest than fat or carbs. Your body only gets 70 of every 100 calories of protein, but it gets 97 of every 100 calories of fat.
  • Rate of absorption: some people have very efficient gut flora that can wring every last calorie out of the food they eat. Those people absorb more calories from their food. Other people have relatively inefficient gut flora, and don’t absorb as many calories from the same amount of food.
  • Accuracy of the label: by law, nutrition labels can vary up to 20% from the actual calorie content of the food. And restaurant meals are notoriously even more imprecise than that. Unless you have a private food lab and you’re testing everything you eat, there’s no way to know for sure.

“Calories Out” is also a lot more complicated than just exercising:

  • Variations in metabolism (the energy needed to keep your heart pumping, your temperature normal, and your body basically functional): even though “metabolism-boosting” tricks are mostly myths, people’s metabolisms can change their calorie consumption by 200-300 calories per day. Metabolic differences include:
    • Muscle mass vs. fat mass (muscle burns a little more)
    • The size of your organs (bigger organs burn more)
    • What your body temperature is (higher temperatures burn more)
    • How much you fidget
    • Genetic differences
    • How much you’ve eaten lately (you have to burn calories to digest food)
  • What you’re using those calories for: your body can preferentially store calories as fat, or it can preferentially use them for energy. What it does depends on hormones and the kind of calories you eat, not the calories themselves.

Then there’s the fact that all of these factors are interrelated. Your body is very, very good at adjusting everything in the system to prevent you from losing weight. Have you ever wondered why people on a diet often feel their hands and feet get cold, or notice that they don’t have any energy? That’s their body, slowing down their metabolism to compensate for their reduced calorie intake.

Taken to an extreme, this can cause some serious problems. In this post, you can even see how the metabolic adaptation to calorie restriction caused one woman to gain weight. You’ve changed “calories in” (by dieting), and you might have even increased “calories out” (by exercising) but your body one-ups you and decreases metabolism so drastically far that it makes up for all the starvation and the time on the treadmill.

So when you add it this all together, the equation is not just “fat gain/loss = calories eaten – calories burned on the treadmill.” “Calories in” are more than food, and “calories out” is more than exercise. In real life, it depends on all kinds of factors, some of which you have no control over and can’t even measure. If you took all those factors into account, then you could construct a useful weight-loss plan based on counting and measuring calories. But you can’t take them all into account – and that’s why calorie-counting fails, even though calories technically still count. In order to produce real-world weight loss, we need to focus on something else.

Objections to Calories-In/Calories-Out

Before moving on to Part 2, take a look at some of the common objections to the CICO theory, and why they’re not convincing.

But nobody eats precisely the same amount of calories every day.

This objection is based on the idea that, if CICO is an accurate model, weight-stable people must be eating the exact same number of calories every single day. And of course this never happens: in the real world, calorie intakes vary a lot.

But this still doesn’t disprove CICO, for two reasons:

  • The fluctuations may cancel each other out. In other words, you might eat 100 calories above maintenance on Monday, but then you might eat 100 below maintenance on Thursday – the net result is no weight gain or loss.
  • As mentioned above, your body is excellent at correcting for these fluctuations. Your temperature will rise and fall, your unconscious energy expenditure (like fidgeting) will increase or decrease. All of these are your body’s ways of matching calories out to calories in, thus balancing the equation.

But I can gain 5 pounds from one cheat day – and I didn’t eat a 17,500 calorie surplus!

Two words: water weight. It would take a 17,500 calorie surplus to gain 5 pounds of fat, but you can gain 5 pounds of water just by eating a lot of salty junk food that causes your body to retain more water. The scale doesn’t know the difference. In your post-cheat guilt, it probably seems like it’s 5 pounds of fat, especially since carrying around all that water weight makes you feel bloated and disgusting. But in fact it is not 5 pounds of fat, and over the next few days, you’ll rapidly drop it all.

But I can’t lose weight even on _____________ calories/day!

This may very well be true. But it doesn’t prove that calories don’t matter; it only proves that counting calories isn’t the best way to lose weight. Remember the insulin-resistant person above, who was gaining weight from eating too many carbs? That person could very well stay fat on 1,200 calories per day or even less. But it’s not because the calories didn’t count; it was because they were storing calories instead of using them. It’s true that thinking about calories won’t help this person lose any weight, but that doesn’t mean the calories don’t matter.


What’s ultimately going on here? It’s clear that calories are the ultimate drivers of weight changes – even the supporters of the insulin hypothesis don’t argue that. But it’s also true that “eat less, move more” completely fails to capture the complexity of how calories are actually used in our bodies. And because we can’t actually control for all the aspects of the “calories in/calories out” equation, calorie restriction is not the best way to achieve long-term weight loss.

In other words, all three of these people are “right:”

  • The dieter who does not lose or even gains weight despite restricting calories. This person’s metabolism is overcompensating for the reduced “calories in” by reducing calories out even more. The net result: weight gain.
  • The dieter who loses weight with calorie restriction, regardless of macronutrient composition. Through a combination of luck and prudence, this person has avoided the metabolic downregulation that usually comes along with reducing calories. She is eating less, but her body is not panicking about the “famine,” and so her body is not reducing calories out to compensate for the loss of calories in. The net result: weight loss.
  • The happy low-carber who has tried and failed calorie-counting, but loses weight with carb restriction despite eating as much as he wants. This person is not as genetically blessed as the lady above. His metabolism does compensate for a loss of calories in, at least as long as his insulin is high. However, with his insulin under control, there is no more artificial “famine,” and his body stops overcompensating for the “food scarcity” by lowering metabolic rate. His “calories out” go up. The net result: weight loss.

All of these patterns are completely legitimate things that actually happen. These are simply different individuals, with different hormonal and metabolic responses to different diets. And they demonstrate very clearly that calories are much more complicated than just the number on the label. Yes, if you want to get technical about it, calories are in fact driving all these people’s weight loss, even the low-carber. But people in the real world don’t care about whether or not calories are technically responsible for their weight loss. They care about what behaviors are responsible for their weight loss. And from that perspective, calories are very often not the solution.

To get even more depth on this issue, Part 2 of this series takes a look at all the reasons why counting calories can fail, why you shouldn’t waste your time and energy on it – and what to do instead.

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