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Are All Calories Created Equal?

20th Oct, 2022


The narrative, especially across social media and the fitness community, tells of simple weight loss via a calorie deficit, calories in versus calories out. Basic laws of thermodynamics. Although this is  fundamentally true, as science is increasingly showing, such a simple equation isn’t always so straight forward. 

A food Calorie (or kilocalorie – kcal – as is used in nutrition labelling) is a unit of measurement of energy, the amount that is required to raise 1 litre of water by 1°C. If we take in excess calories that are needed for the body’s energy requirements, they are stored as fat. Over the long term, this can accumulate leading to obesity. 

Though all foods contain a discrete number of calories, the amount that can be utilised by the body vary from food to food. Hence, not all calories are created equal. 

It was back in the 1880s that the calorie as we know it today was discovered by the scientist Wilbur Atwater. He determined the average caloric content of the 3 main macronutrients:

Macronutrient Kcal Content (Atwater Values): Carbohydrate 4 - Protein 4 - Fat 9

These are the same values that we still use today, however, there are many arguments to suggest that even how we calculate and understand calories in the first place is likely flawed.

Caloric Density and Availability

When we refer to caloric density, we mean how many calories are present per volume of a food. Using the numbers above, you can see that between macronutrients, fat is more calorically dense than protein and carbohydrates. Often, we see that processed foods, like crisps and biscuits, are more calorically dense than unprocessed foods thanks to the addition of sugars and fats to improve their taste. These processed foods that are dense in calories are commonly low in nutrients, so called ‘empty calories’. 

This creates problems when it comes to caloric availability. Caloric availability is a little less known in general understanding and relates to the amount of USABLE calories that we can actually get from food.

Macronutrient Kcal Content (Atwater Values): Carbohydrate 4 - Protein 4 - Fat 9
Macronutrient Caloric availability - % of accessible calories in food: Carbohydrate 90-95% - Protein 70-80% - Fat 97-100%

Caloric availability results from many factors, but largely relates to how hard or easy it is for the body to digest the food, being the amount of energy (kcals) is required to break it down.  

As a general rule of thumb, the more you process a a food, the caloric availability increases. You could see processing as doing part of the digesting for you, so your body doesn’t have to work so hard to access the calories out of it.

Consider sweetcorn compared to tortilla chips, often sweet corn kernels come out the same way they went in, making the calories completely inaccessible, whereas, in tortilla chips, the corn has been ground down and cooked, doing most of the digestive work for your body already. Hence you will get many more calories out of the chips than the wholefood. Meaning it’s not just how many calories you're eating, but where those calories are coming from that determines the net amount that you consume. 

Take Away

So, the current caloric system is broken. Why? Because the nebulous Atwater values that all nutrition labels are based on don’t consider 3 main factors: fibre, food-induced thermogenesis (heat created by the body during digestion) and the energy cost of eating the different macronutrients. Though there are other components effecting how we access and utilise calories, like hormones, gut microbiome, time of eating and genetics, these are more complex still and not yet fully understood. 

At the end of the day, we need to remember we eat FOOD not CALORIES. This is why at TYME, all the meals are cooked from scratch using the highest quality food ingredients. We like to think of counting the amount of nutrients and plant fibres as a priority, where each meal naturally comes in at a healthy caloric value thanks to the minimally processed ingredients.

By Lulu Gibbons

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