What’s the Point of Counting Calories?

Nutrition Diva listener James writes:

I was wondering if you could devote an episode to calories: how they’re measured, how we process them, what a bomb calorimeter is, and all the problems with counting calories.

What do calories measure? 

A calorie is a unit of measure, like an inch or a kilogram. Only instead of measuring length or weight, a calorie measures energy. Technically, a calorie is the amount of energy it takes to raise one gram of water by one degree Celsius.

Calories can be measured by something called a bomb calorimeter. You might have even built a crude version of a bomb calorimeter in science class. In broad strokes, you submerge a chamber in a bucket of water and put a thermometer in the water. Inside the submerged chamber, you set something on fire. The heat generated by the combustion raises the temperature of the water in the bucket, which you can measure with the thermometer. You can then calculate the amount of energy or calories were in the thing you set on fire. 

If we habitually take in more energy than we use, we gain weight. So, we use calories as a guideline to determine how much food energy a person needs.

We used to use bomb calorimeters to calculate how many calories a given food contains. These days, however, it’s more common to estimate the number of calories based on how much protein, fat, and carbohydrate a food contains.  (These amounts can be determined through chemical analysis.)

When we’re using the word “calorie” in relation to food, by the way, we’re actually referring kilocalories.  Sometimes you’ll see calories abbreviated as kcal and that’s what that refers to. When we say that a food that contains 60 calories, it technically contains 60,000 calories. But all those zeros would would be a pain to deal with so we just lop them off. This drives phycisists and chemists absolutely nuts.

Why do calories matter? 

Just like in that bomb calorimeter, our bodies combust food to release its stored heat or energy. We then either use that energy to power our biological processes or, if we have more energy than we need, we store it for future use. If we habitually take in more energy than we use, we gain weight. So, we use calories as a guideline to determine how much food energy a person needs. We need enough to fuel growth and maintain function, but not so much that we start storing a lot of fat.

There are calculators that can estimate your daily calorie needs, taking into account your age, sex, height, and activity level. And then there are databases and labels to tell you how many calories are in various foods.  However, as listener James suggests, there are a few problems with this system.

Calorie estimates can be inaccurate

Let’s say you plug your details into an online calculator and learn that you use 1847 calories per day. Take that number with a truckload of salt. Energy expenditure varies hugely from person to person. Even if you and I are the exact same height, weight, age, and sex and do the exact same workout, you may burn 400 calories more or less than I do.

Energy needs can be affected by diet, genetics, body composition, hormones, drugs, and a million other factors. And just to make the whole situation a little more ridiculous, those readouts on your treadmill, Peloton, fitwatch, or diet tracker that tell you how many calories you burn doing various activities are only slightly more accurate than asking the Magic 8 Ball.

But wait, there’s more.

Those readouts on your treadmill, Peloton, fitwatch, or diet tracker that tell you how many calories you burn doing various activities are only slightly more accurate than asking the Magic 8 Ball.

Calorie counts for foods are also unreliable

The numbers listed in your your calorie counting app represent average values for foods. Even if you are measuring or weighing your food with great precision, this apple may be a bit sweeter than average, that banana might be a little less ripe, this nut may have a bit more fat. Even for packaged and processed foods, the calorie count shown on the Nutrition Facts label is just an average. A variation of +/- 10% would not be surprising.

Even for packaged and processed foods, the calorie count shown on the Nutrition Facts label is just an average.

Secondly, those calorie counts are estimated using formulas that may or may not be 100% reliable. It was recently discovered, for example, that the standard formulas that were in use for most of the last 100 years over-estimated the amount of energy that humans are able to liberate from nuts. More modern methods suggest that almonds provide about 20% less energy or calories than previously thought.

Finally, our bodies are not bomb calorimeters. Like a campfire that might go out and leave a few unburned chunks of wood, our bodies don’t extract all the energy from our food. Some unknown and variable amount of that energy will pass through us unabsorbed. 

So what’s the point of paying attention to calories?

Once you realize how fuzzy these numbers are, it’s clear that there’s really no point in counting every calorie. So, how are we supposed to know how much to eat? Can we just rely on our hunger or satiety signals to tell us if we need food and when we’ve had enough? Probably not.

RELATED: Is Intuitive Eating the Answer to Weight Loss?

There are so many foods available that are literally engineered to override our satiety signals. Advertising, habit, and social cues can trigger feelings of hunger even when we are not even remotely in need of food. For most of us, deciding when, what, and how much to eat in the modern world requires some prefrontal cortex activity. And here’s where calorie counters might come in handy.

RELATED: How to Tell If You’re Really Hungry

How to use calorie counters

It’s useful to understand that a bowl of fruit has only a fraction of the calories of a bowl of jelly beans.

It may be useful to know the relative energy density of foods.  Even if we can’t say exactly how many calories that pile of French fries contains, it’s helpful to know that it contains about 10 times as many calories as the same size pile of celery sticks.  The caloric difference between a serving of berries and a serving of watermelon probably doesn’t matter in the big picture. But it’s useful to understand that a bowl of fruit has only a fraction of the calories of a bowl of jelly beans.

I also find it helpful to have a guide to portion size. For example, it would not be that hard for me to eat an entire pint of Haagen Dazs. But when I see on the label that this would be about half the number of calories that I should be eating for the entire day, cooler heads (usually) prevail. I’m not going to get out my kitchen scale to be sure that I eat exactly 100 grams of ice cream and no more. But I’m not going to eat whole thing either.

Now that calorie counts have been added to so many restaurant menus, I’m often surprised to see how many calories something contains. Sometimes, I’m even wrong about which of several choices is higher or lower in calories. (And I’m a professional calorie estimator!) Very often, seeing those numbers causes me to change my mind. That little tart might seem like a perfectly harmless little snack to enjoy with my afternoon tea…until I see that it actually contains an entire meal’s worth of calories.

These are all valid and useful ways to use calorie information. Just keep in mind that all of these numbers—how many calories you supposedly need, how many calories various activities allegedly burn, how many calories various foods contain—all of these are really just estimates.

That little tart might seem like a perfectly harmless snack to enjoy with my afternoon tea … until I see that it actually contains an entire meal’s worth of calories.

How to lose weight without counting calories

The most reliable and accurate indicator of whether or not you are taking in the right amount of energy is what’s happening on the bathroom scale. (Or, if you prefer, in the waistband of your favorite jeans.) Whatever you’re monitoring, keep in mind that changes from one day to the next are not due to fat loss or gain. These reflect much more transient changes in water and digestion.

If your jeans are feeling tighter and tighter every week, it’s because you are taking in more calories than your body uses.

This is why I suggest using a moving average to track your weight. This will smooth out those meaningless ups and downs and reveal the true trend. If your weight is trending up or those jeans are feeling tighter and tighter every week, it’s because you are taking in more calories than your body uses.

But the answer isn’t to start counting, weighing, and measuring every calorie or to pledge to burn every excess calorie off through exercise. That’s a ticket to crazy town.

If you need to take in fewer calories, use calorie counts as a guide to which foods might fill you up for fewer calories or which ones need to be eaten in smaller quantities. I have more ideas on that in my episode on how to eat less without feeling hungry as well as my two-part episode on satiety and satiation.  On the other side of the equation, look for opportunities to be more active throughout the day. Get-Fit Guy Brock Armstrong has a great podcast on how incidental movement, and not exercise, is actually the key to getting fit.

These strategies won’t lead to fast weight loss, but trust me, you don’t want them to.

RELATED: The Case for Super Slow Weight Loss

Call the Nutrition Diva Hotline

Have a question you’d like answered on the podcast? Call the Nutrition Diva listener line at 443-961-6206 and leave me a message! Then be sure to subscribe to the podcast on Apple Podcasts, Stitcher, Spotify, Google Podcasts, or wherever you like to listen.