Is A Calorie A Calorie?

Is a calorie a calorie?
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This might sound crazy to some, a calorie isn’t a calorie? That’s as confusing as saying 1+1=3…

Please bear with me… There is a reason why I’ve answered this question as no. In basic terms, a calorie is the energy needed to raise the temperature of 1 gram of water through 1 °C. If we were to look at this question in a one dimensional manner, only considering this definition of a calorie – the answer would be “Yes”. However, when the human body is concerned you have a number of other factors to take into consideration – nothing is quite so one dimensional.


First of all, to understand this concept that a calorie may not be a calorie, we must first look at the macronutrients (exc. Alcohol) and their calorific value:

Fat: 9 Kcal/g

Carbohydrate: 4 Kcal/g

Protein: 4 Kcal/g

When you are looking at these 3 macronutrients, you can see that fats are more calorie dense, whereas carbohydrates and protein share a similar concentration of calories per gram. Now whilst protein contains 4 Kcal/g, the amount of energy your body pulls from the protein you consume is actually very little. Protein is not the body’s preferred source of energy, and the process of using protein/amino acids is actually quite “expensive” to the body. It much prefers using carbohydrates and fat as an energy source. As such, protein is rarely broken down for use as energy. In addition, the amino acids within the protein you consume are typically used to promote the repair of muscle tissue (if you are training regularly). Subsequently, a calorie from protein is very different to a calorie from carbohydrate and fat.

Furthermore, protein has a more pronounced thermogenic effect of food, when compared to carbohydrates and fat. Thermogenic effect of food is the process by which the body’s temperature raises.  This process of an increase in body temperature causes a calorific expenditure itself. The fact that a large number of calories are coming from protein in someone who is “dieting” or looking to reduce body fat, means that these calories may be slightly skewed by this thermogenic effect of food.


Digestion of other macronutrients may also change the notion of “a calorie is a calorie”. Some foods are much more satiating than others, as such you simply wouldn’t want to consume the same number of calories. For example 500 kcal from oats are a lot more satiating than 500 kcal from chocolate. As such, you are less likely to eat later in the day, changing the number of calories you consume over the day. Whilst this doesn’t change the fact you are consuming 500 kcal from either food. The calories (or nutritional breakdown) of the oats make it much more satiating, and much more likely to fill you up, and less likely to consume calories within the following hours. This makes high satiety foods much more beneficial to consume when dieting, or on restricted calories.

Judging food quality by its calorific density is common, however it may also be worth looking into the micronutrient content of foods. The notion that “A calorie is a calorie” may change the perception of the quality of the food you are consuming. Some foods may be more vitamin and mineral dense – therefore serving a great purpose in the diet… however may not be a great source of macronutrients. To make this clearer, 100 kcal from spinach will provide a great source of vitamins and minerals when compared to 100 kcal of sweets – which contain virtually zero… however sweets would be a dense source of carbohydrates.

Throughout the digestion process, calories from each macronutrient can have differing effects on the body. Carbohydrates (high GI carbohydrates specifically) can have a large impact on insulin levels. Due to being digested quickly, insulin rises rapidly in order to deal with the blood sugar rise. Insulin is responsible for the transport of glucose in the blood to be used as energy, or move the energy to be stored if it’s not required at that specific time. Fluctuating insulin levels on a regular basis makes it more likely that you will gain body fat. As such, calories from carbohydrates can have a much different effect on the body, when compared to other macronutrients – this suggests that calories from carbohydrates could be different to calories from fats or protein.


Timing of certain foods can also make a “calorie” at one time, more beneficial than the same “calorie” at another. Post-workout is a great example of this – when you finish a workout it is beneficial to recovery and, for muscle growth, to consume a fast digesting source of protein and carbohydrates. At this specific time, when your body is depleted from training, and insulin becomes your friend, it is important to consume these fast release carbohydrates as they help to replenish depleted muscle glycogen and support the repair of damaged muscle tissue (alongside protein).

However, as discussed in the previous paragraph, if you were to consume fast digesting carbohydrates at other points in the day (perhaps between meals) it could have a more negative effect, more likely to be stored within the body rather than being used at that time. This shows that calories from certain sources can be utilised differently at different times – showing a calorie is not always having the same effect.

So, to conclude, when looking at a calorie, it is important to consider that it is not quite so one dimensional; macronutrients, timing and digestibility all play an important role in making some calories different to others. This shows that whilst counting calories and macronutrients can be extremely productive to reaching your end goal, the quality and timing of foods can be just as important.

About the Author

Rowan (BSc Hons Sport and Exercise Science) works within the BULK POWDERS™ Product Team. His role includes being responsible for Product Quality as well as contributing to Product Development.

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