- I think this whole calorie thing might be bull- - Bologna (upbeat music) - Whoa!

First off, the number that they write on the label here only has to be accurate within 20%, 20%!

That means that 150 calories per serving could actually be anywhere from 120 to 180 calories per serving.

That is a pretty wide margin, but there's a reason that it's so wide.

Turns out calories are actually way more complicated than I ever imagined.

Calories are supposed to tell you how much energy is in your food.

And energy is important.

You need at least some of it just to survive.

And if you're active, you need more of it.

But if you're getting too much energy, (bag crinkles) your body can store the excess as fat, which causes its own problems.

What you really want is to balance your body's energy needs with the energy that you get from your diet which is why people often turn to counting calories.

A calorie is just a measure of energy that can be in food but also in things like gunpowder or gasoline.

One calorie is the amount of energy needed to raise the temperature of one gram of water by one degree Celsius.

So if you want to know how much energy is in a given amount of gasoline, you would burn it, measure the heat, given off, and then calculate the number of calories that were there to begin with.

And that's actually how food calories were originally measured too.

With something called a bomb calorimeter or combustion calorimeter.

You put food into a sealed container that's surrounded by water, then you heat up the food until it completely burns away.

That heats up the water, so the water's temperature goes up.

Based on how much it goes up, you can figure out the number of calories in that food.

(screw gun shrilling) (upbeat music) (can lid hitting counter) (screw gun shrilling) (upbeat music) (upbeat music continues) So I'm lighting this peanut on fire and the energy from that burning peanut will heat up the water in this smaller can.

And by measuring how much hotter the water gets, we can estimate how much energy was in the peanut.

It hit 40, that's crazy!

Oh my gosh, it just like.

(laughing) One peanut starting temperature was 24.9 degrees Celsius.

And it is at 40.0 degrees Celsius.

So that's 15 times 0.2 liters which gives you three calories.

One peanut, three calories.

Not so surprisingly, the grape would not catch on fire.

(same upbeat music as previous) Wow!

It's going up fast!

Woo!

(upbeat music continues) 29.0, that would mean it's about a calorie, for one Cheeto.

(laughing) (upbeat music continues) The muffin's are going to be a tricky one.

Let's move on to cheese.

The cheese is bubbling.

It's melting everywhere.

It's not going to light on fire.

3 pretty obvious failures, but the Cheeto and the peanut were awesome, they totally burned.

So that's basically how they used to measure energy and food.

One of the pioneers of this early nutrition chemistry was a guy named Wilbur Olin Atwater.

Atwater developed some of the first dietary standards using a bomb calorimeter, but he knew there were two big issues that made his numbers less accurate.

First, a person's nutritional needs will vary based on age, sex, activity level and body size.

And it's tough to account for that.

The second problem was that caloric intake is only part of the picture.

What matters isn't how much energy is in your food, it's how much energy your body can get from that food.

These are two different things.

Like you can burn a piece of wood, and get a lot of heat out of it.

That wood contains a lot of energy but if you eat the piece of wood, your body can't use most of that energy.

Also, most tree wood is not edible, so don't do that.

To figure out how much energy our bodies actually use from food, Atwater figured he needed to subtract the amount of energy leftover after we've digested the food.

Yeah, so he ran an experiment.

He fed people, a variety of foods and used his bomb calorimeter to measure how much energy was in those foods.

And then he's the bomb calorimeter to measure how much energy was left over in people's feces and urine.

Subtract that second number from the first, and you can see how much energy that person's body used from that food.

(upbeat music) Uh, no.

He used that data to come up with a simple equation.

Carbohydrates give your body four calories per gram.

Fats give your body nine calories per gram, and proteins, four calories per gram.

That's it.

Regardless of what food you're talking about add up the carbs, fat and protein and you have a pretty good estimate for how much usable energy is in that food.

(upbeat music) 4 times 7.

Times 4.

According to the Atwater method, it should be 4.4 ish calories per peanut and 7.5 ish calories per Cheeto.

The Atwater equation was actually very close to what's written on these packages, which is not so surprising but it was cool to see.

What I was surprised about was that the bomb calendar going to reading for peanuts was really close to the Atwater equation and what's written on this package.

Plugging numbers into an equation is much easier than having to burn your own food and feces and urine.

And it's a lot cleaner, but the 4-9-4 equation's not perfect.

Atwater only used a few subjects per experiment, which means calorie consumption for the average person is based on very few people.

That's a problem because the way I process food isn't the same as the way my sister processes food.

Isn't the same as the way you process food.

Atwater also fed subjects a mix of different foods, so he was getting an average for that too which is fine if you're eating a widely varied diet.

But there's a lot of variability between foods that this equation does not account for and how we process foods can change on a daily even hourly basis.

Today, I'm inside and snacking.

What if tomorrow I might start off my day with a long run.

We'll see.

if we want to make things extra complicated, calories can vary even within a single type of food.

A grape grown in Australia might be very different from a grape grown in France.

I mean, even two grapes on the same bunch might have slightly different numbers of calories, which is why the number of calories in something and our obsession with calorie counting is eh.

We know it's not completely accurate.

Scientists have actually come up with more accurate methods but for now we're sticking with the 4-9-4 method because it's much easier and more practical.

And when it comes to health, the number of calories isn't as important as the source of those calories, the healthiest calories come from fruits, vegetables, whole grains, and lean meats.

I talked to a nutrition researcher and he said the best thing we can do is focus more on what we're eating and less on this.

(upbeat music)