Quick Summary tl;dr
Calories in food are measured by bomb calorimetry, which doesn’t apply well to human biology because our cells use a very different process to extract energy.
We all have different microbiomes, which uniquely influence how we extract energy from food.
The law allows for a 20% margin of error on nutrition labels.
Exercise contributes to a small proportion of calories burned. Far more energy is burned by temperature regulation, fueling your brain, digestion itself.
NEAT refers to non-exercise related calorie burning activities, like bouncing your leg. Variations in NEAT account for a large variation among humans in calories burned.
Hormones govern how your body uses and distributes energy over the long term.
For the above reasons, you can’t accurately measure “calories in” or “calories out.”
What is a Calorie?
A calorie is a unit of energy. Specifically, a calorie is the amount of energy required to heat up 1 gram of water by 1 ℃. Technically speaking, each “Calorie” in food, denoted by the big “C” is equal to 1,000 little “c” calories, but that’s besides the point. The question we should ask is, why is a calorie defined as the amount of energy it takes to heat water?
It all has to do with how calories are measured in food. The technique used to measure the calories in, say, a banana, is called bomb calorimetry.
Literally, you take the banana, place it in a chamber surrounded by water, and blow it up. KABOOM! Energy is released from the combustion into the surrounding water, and the number of ℃ the surrounding water is heated tells us how many calories are in the banana. But can you apply this value to human biology? Well, not really.
How Do We Extract Calories from Food?
Our bodies don’t extract energy like bomb calorimeters. Once the nutrients in our foods make their way to our cells, energy is extracted in a more sophisticated manner than simple combustion.
Food is methodically broken down by an orchestra of enzymes to generate cellular building blocks and liberate electrons that can then be systematically harvested for energy by mitochondria. Jargon aside, we are not bomb calorimeters. Not even close!
What’s more, for every you cell in your body, there is at least one bacterial cell residing in your gut’s microbial ecosystem that also has a role in extracting energy from the food you eat.
Why We Can't Accurately Calculate Calories in Foods
Since we all have different “microbiomes,” we all extract energy from food differently. As an extreme example, if you were a gorilla with a gorilla’s microbiome, you could get 60% of your calories from fiber ( 1)!
True, we aren’t gorillas, but the concept is the same. We each have unique microbiomes and each extract energy from food differently (2). Since we were talking about fiber, let’s use fiber as a case in point. Although fiber is thought to contain no calories, we can indeed extract calories from fiber (or, more correctly, our gut bug friends can for us), in the form of short chain fatty acids ( 3).
As a goofy thought experiment, let’s do some math! That gorilla paper I referenced earlier states that humans can get somewhere between 2 and 9% of our calories from fiber ( 1). If you scale that 7% difference to a 2,000 Calorie diet, that’s 140 calories per day or 51,100 Calories per year. If you want to visualize that, it’s about the equivalent at 64 sticks of butter (as measured by bomb calorimetry).
Obviously, that’s just a goofy thought experiment, but it proves a point: humans are heterogeneous, specifically with respect to our microbiomes, and that complicates the calculation of “calories in.”
Let’s play devil’s advocate and assume that we can perfectly measure calories by blowing up bananas and apply those caloric values to human nutrition. Then would we be able to count calories? Still no. At least in the United States, the Food and Drug Administration’s Guidance for Industry allows for a 20% margin of error on nutrition labels ( 4). Even if food companies actually abided by this law, which many don’t, that would amount to a 400 Calorie error on a 2,000 Calorie diet.
So, let’s summarize. You can’t count calories eaten accurately because:
- you’re not a bomb calorimeter,
- you have a unique microbiome, and
- nutrition labels aren’t accurate.
You can’t count calories eaten accurately because you’re not a bomb calorimeter, you have a unique microbiome, and nutrition labels aren’t accurate.
Why We Can't Accurately Calculate Calorie Expenditure
That’s only half of the equation. Advocates of strict calorie counting provide the logic that calories in – calories out = weight gained.
We’ve talked about calories in, which can’t be accurately measured, but what about calories out or burned?
Here, things get even more messy. One could write an encyclopedia on the topic of why measuring calories burned in humans over an extended period of time is so complicated, but I’ll just mention a few highlights.
To begin, physical exercise only accounts for a tiny fraction of total calories burned for most people. Much more energy is spent on the biological processes of temperature regulation, running your brain, and digestion. Furthermore, “non-exercise activity thermogenesis,” or NEAT, also burns more calories in a day than exercise for most people.
NEAT refers to those physical movements that are separate from exercise, like maintaining good posture or bouncing your leg or gesturing with your hands. NEAT activities amount to far more, in terms of calories, than the 30-60 minutes a person might spend at the gym and is enormously variable among people.
In one study, published in the prestigious journal Science, 16 healthy weight individuals were hyperfed 1,000 Calories per day more than their estimated need for 8 weeks. Quoting from the paper, “Changes in NEAT accounted for the 10-fold differences in fat storage that occurred and directly predicted resistance to fat gain with overfeeding.” ( 5) I’m not even going to digest that for you. Just pause, and think about it!
Now, a question: Do you know people what are fidgety or bounce their leg a lot? Are they skinny?
Perhaps most importantly, the human hormonal system governs how energy is distributed and used. Over the long term, this is enormously important. Your hormones determine if you expend energy or store it. And, if you store it, your hormones determine how you do so, as fat or lean muscle.
Because fat and muscle mass impact hormones, this then creates a cycle. Your hormones determine how your fuel is partitioned. The partitioning of fuel effects your hormones and your metabolic rate, and so on. It becomes a dance among insulin, testosterone, estrogen, ghrelin, thyroid, muscle, and fat that makes counting calories a futile effort over the long term.
So, let’s summarize. You can’t count calories burnt accurately because:
- Exercise contributes to a small proportion of calories burned, compared to other functions.
- Your body adjusts NEAT to adjust calories burned.
- Your hormones determine if you expend energy or store it, and if you store it, how you do so.
You can’t count calories burnt accurately because exercise contributes to a small proportion of calories burned, and your hormones determine if you expend energy or store it.
Count Calories Cautiously
Having said all that, this little blog isn’t going to stop calorie counters from counting, at least not without a viable alternative. So, here are a few suggestions to try instead if you want to lose weight:
Alternative 1: Count Carbs
It’s no secret anymore that the key to controlling weight is controlling carb intake (here's an app for that). In fact, it’s been shown than trading carb calories for fat calories increased “calories out” by about 52 Calories per day for each 10% swap (i.e., 200 carb calories for 200 fat calories on a 2,000 Calorie diet) (6).
Take as many net carbs (exclude fiber) as you’re eating right now and cut that number in half OR reduce your net carbs to 20 grams per day.
Alternative 2: Count Meals
Snacking is the devil when it comes to weight gain. In addition to reducing carbs, you can reduce your levels of fat-storing insulin by eating less frequently.
Try counting your meals or “feedings.” Anytime you eat something with macronutrients, that’s a feeding. Play meal golf as see if you can hit a birdie or two meals per day (par would be 3, given breakfast, lunch, and dinner).
Alternative 3: Count Hours
Try time restricted feeding or intermittent fasting. Starting with eating only inside a 12-hour eating window. Then see if you can reduce that window to 10, 8, or even 6 hours. I find, for a lot of people, this is easier than it sounds. Once you have your window determined, decisions become easy. It’s outside your window, therefore no food. Your body instead must rely on your stored body fat. Don’t worry, it learns.
Alternative 4: Count Glycemic Index
If the above alternatives sound way too strict for you, and you’re not someone who intends to go low-carb or keto, then perhaps try just eating carbs that are lower in “glycemic index” (GI).
The GI of a food refers to how much it spikes your blood sugar. (If you’ve also heard the term Glycemic Load, this refers to GI times the amount of food you eat. GI is like density, GL is like mass.) The higher the GI, typically, the higher your insulin goes up, then crashes. (There is more nuance here ( 7) and, as a scientist, I think I’m ethically obligated to apologize to Eran Segal, but let’s not go down a rabbit hole.)
This spike and drop in insulin, referred to as the insulin roller-coaster, causes “hormonal hunger.” Basically, your body isn’t really hungry for nutrients, which is “nutritional hunger.” Instead, you’re being deceived by fluctuation in hormones. In fact, it’s even been observed that changing the GI contents of a meal, without changing the meal’s taste, calories, or macronutrients, impacts the insulin roller-coaster and this alters activity in the brain’s reward center, the nucleus accumbens (the same region that lights up in response to cocaine), to trick people into “hormonal hunger” ( 8).
So, check out the GIs of your favorite foods and make smart choices. For reference, a carbless egg has a GI of 0, broccoli is about 15, watermelon is 72, and pure sugar is 100.
Let’s do like a sushi chef and wrap it up. Here are the key takeaways…
Counting calories is like trying to pogo-stick a marathon, it might seem like it’s working at the beginning but will probably fail long-term. Here’s what to know about counting calories.
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