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How Can Diet Coke Have Zero Calories? [Bad For Weight Gain?]

how can diet coke have zero calories

In a world where people are concerned about their weight and calorie intake, finding a low or zero calorie treat that also satisfies seems like a never ending quest.

After all, celery and ice berg lettuce are both low calorie snacks, but they aren’t exactly the most satisfying things to munch on.

Sometimes you just crave something sweet and fizzy.

So you reach for a Diet Coke and notice that a 12 ounce can has zero calories. How exactly does that work?

How can Diet Coke have zero calories?   despite being sweet and fizzy and satisfying to drink?

It’s true, Diet Coke has zero calories.

And it can do that because it takes some chemical shortcuts to remove and replace the main caloric component in Classic Coca-Cola.

That caloric ingredient is, of course, sugar.

Diet Coke replaces the sugar with a low calorie substitute, aspartame.

By doing so, it turns a soft drink that normally has 240 calories into a zero calorie drink.

To understand how this happens in detail, we need to discuss what calories are precisely, and how they are calculated.

Here is a quick video explaining exactly why soda can have zero or low calories

No you’ve watched that let me explain further below.

What’s in a Calorie

The first thing that you should understand is that when you see a food label and it says 300 Calories (note the capital C), it actually means 300 kilocalories, or 300,000 actual calories.

That’s because the unit of a single calorie is so small, that it actually doesn’t really mean much.

To get to a meaningful degree of measurement, The food industry decided that for the sake of calculation, using Calories (meaning kilocalorie) instead of calories would be easier for everyone.

So what is a calorie?

A calorie is a unit of energy. It is the amount of energy that is required to heat 1 gram of water by 1 degree Celsius.

So a Calorie is the amount of energy required to heat a kilogram (or a single liter) of water by 1 degree Celsius.

This unit of measurement was invented by Antoine Lavoisier, who originally used the term to describe the internal temperature and heat of the human body.

So now that you know what a Calorie is, you’re probably wondering how they are calculated.

How are Calories Measured?

Originally, calories from food were measured using a calorimeter.

This device was essentially a sealed chamber surrounded by water.

A piece of food that was dehydrated was placed inside the chamber and set on fire.

The temperature of the surrounding water was tracked, and based on how much the temperature rose the number of calories in the food item was calculated.

At first, this was fine, but as our understanding of the body and how it digests foods advanced, several problems began to creep in.

For example, a piece of whole grain bread with high fiber content is going to also ignite the fiber.

That will cause a miscalculation of the Calorie content , because we now understand that fiber is not absorbed into the blood stream, and therefore shouldn’t count toward the number of Calories in the bread.

Modern calculations are done using the Atwater indirect system, which does a calculation based on the energy-producing macronutrients that a piece of food contains. The macronutrients that are tracked are fat, protein, and carbohydrates.

Alcohol is also tracked, despite not really being a nutrient, but it is a significant source of calories.

When carbs are calculated, the mass of fiber is also calculated and its caloric contribution is subtracted.

The Atwater system uses the following values for the macronutrients in foods
  • Alcohol: 7 Calories / gram
  • Carbohydrates: 4 Calories / gram
  • Fat: 9 Calories / gram
  • Protein: 4 Calories / gram

The values for these substances were calculated by placing them in a modern calorimeter and represent the averages of the various substances.

That’s because different sugars will produce varying amounts of energy depending on whether they are simple or complex sugars.

Bringing it All Back Together

So, understanding how a Diet Coke becomes a zero calorie drink comes from looking at the nutrition label and seeing what the total count of the macronutrients is in it.

And if you look, you can see that Diet Coke has 0 grams of fat, 0 grams of carbohydrates, 0 grams of protein, and 0 grams of alcohol (although that is understood, even if it’s not directly listed).

That means that according to the Atwater Indirect System, because Diet Coke has zero macronutrients, it has zero calories.

You might wonder if the calorie count only counts those four macronutrients, what about the other ingredients in Diet Coke. Don’t they at least have some caloric value? Let’s take a look at the ingredient list to see what they are and look at how many calories are in each.

What’s in that Diet Coke?

what's in your diet coke

According to the Coca-Cola website, the ingredient list for Diet Coke is the following:


Going through the ingredients one by one we can find that there really are no significant sources of calories to be seen.

Let’s explain.
    • Carbonated Water is just water that has carbon dioxide forced into it by high pressure.
      • We know that water doesn’t have any calories, and neither does carbon dioxide.
      • Therefore, carbonated water has zero calories.
    • Caramel Color, according to org (the Food and Agriculture Organization of the United Nations), in soda is made from sulfite ammonia, and is prepared by heating carbohydrates near sulfite and ammonium compounds.
      • We know that from the Atwater system that carbohydrates have 4 Calories per gram, so does the caramel color add any caloric content to the Diet Coke?
        • The short answer is no. And that’s because when you heat the carbohydrate near the ammonium and sulfite compounds, you change the chemical structure of the carb so that the body can no longer absorb it or break it down for energy.
        • Hence, caramel color adds zero calories.
    • Aspartame is an artificial sweetener that has the chemical formula of C14H18N2O5.
      • From the chemical formula and the molecular shape, we can see that it’s actually an amino acid, and thus is a protein.
        • From Atwater, we know that you get 4 Calories per gram of protein. So how much aspartame is in a 12 ounce can of Diet Coke?
          • A can of Diet Coke contains 180 milligrams of aspartame, so from the aspartame, the Diet Coke gets 0.72 Calories.
    • Phosphoric Acid and Potassium Benzoate are both compounds that are not able to be metabolized, so they don’t add any calories either.
    • Natural flavors are essences of things found naturally and add flavoring, but not any significant nutritional value.
      • This is a mandate handed down by the FDA, and ensures that there is truth in labeling.
      • Because they add no significant nutritional value, they also add zero caloric content.
    • Citric Acid is used in metabolism, but doesn’t contribute anything nutritionally to the human body.
      • Instead it is used in combination with the enzyme citratase to produce oxaloacetic acid and acetic acid, which are then used as part of amino acid synthesis.
        • So Citric Acid adds zero Calories.


  • Caffeine is a compound that acts as a neurotransmitter agonist and is not metabolized for energy.
    • Therefore it also has a zero calorie addition to the Diet Coke.

So, looking at all of the ingredients, the only ingredient that adds any Calories is aspartame, but it only adds 0.72 Calories.

As this total is under 1 calorie, according to the FDA, Coca-Cola is well within their rights to call Diet Coke a zero calorie drink.

Putting It Together

can of zero sugar coca cola

Diet Coke is a zero calorie drink because of the removal of the sugar and replacing it with aspartame, which provides only a fraction of the calories.

The rest of the ingredients in both Classic Coca-Cola and Diet Coke are negligible in their caloric additions.

Even though Diet Coke is a zero calorie drink, it should still be considered an occasional treat.

This is because of the caffeine and Potassium Benzoate preservative.  You may wish to consider alternative drinks such as creating flavored water with sodastream.

If you have any questions, please let drop me a note.