Confused About Calories? Let’s be Clear Once & For All


Confused about Calories? If it fits your macros, all calories are created equal and protein vs. carbohydrate diets it’s no wonder people are confused about calories! This article sets out to help explain the difference in calories in the different macronutrients. Otterburn (1994) shown the caloric availability IN HUMANS of fats from coconut and corn oils to be 7.8 and 8.5 respectively. If you know your calorie values of different macronutrients you will see that this is not quite the normal 9 calories per gram of fats.

Why do fats have a higher calorie content?

Ever wondered why fats have a higher energy yield per gram compared to that of proteins and carbohydrates? It is because of the high carbon to oxygen ratio and it needs less oxidisation than that of proteins and carbohydrates. Stored in non-solvated form, where water contributes far less to the reaction than that of proteins and carbohydrates. In contrast hydrated glycogen binds water up to three times its molecular weight and water does not contribute any free energy in these reactions. Of note, anhydrous (free from water) glycogen yields almost two-thirds more energy than that of hydrated glycogen. Triacylglycerols yield far more energy, but when applied to a biological system it gets a bit trickier.

What is a calorie?

It is interesting to see the Evidence Based Practitioner’s back track on their positions of “a calorie is a calorie.” Ever wondered how calories are measured? Calories are measured traditionally by placing a dried food into a bomb calorimeter. The food is ignited and completely burned, and the heat given off is measured. One calorie equals the amount of heat it takes to raise the temperature of one kilogram of water by one-degree Celsius. However, most food manufacturers use the Atwater system, where calories are not determined by a bomb calorimeter but by the average values of calories per grams of proteins, carbohydrates, fats and alcohols. The manufacturers probably use databases to gather that information. Two problems here (1) the human body is not an inferno, there are biochemical reactions to consider here (2) the Atwater system uses assumed calories. It is no wonder food manufacturing labels are out as much as 20/25%.

Are calories from carbohydrates, proteins and fats all the same?

Regardless of the above statements when someone says a “calorie is a calorie” and they are applying that principle against the human body they are in error. Of course putting the calorie is a calorie model into a calorimeter you can say a calorie is a calorie, however the different chemical reactions to digest and metabolise the calories from the different macronutrients varies in biological systems and is dependent on the type of diet you are on and the diversity of your microbiome (just to complicate matters more).

We’ve previously discussed fats and why they have a higher calorie value that being 9 calories to 1 gram of fat, but what of proteins and carbohydrates both having 4 calories per 1 gram? Carbohydrates are stored efficiently in chained glucose molecules in carbohydrates called polysaccharides. Enzymes in the mouth and stomach start to break these glucose molecules away from the polysaccharides and the glucose can be absorbed in the intestines and then used by the body. The chemical reactions need bond disassociation energy (the energy needed to break down the chemical bonds) in the digestion process and once this has happened the body needs more bond disassociation energy to use glucose. Proteins are chains of amino acids called polypeptides, digestion involves the release of hydrochloric acid in the stomach to decrease pH  to activate pepsinogen to pepsin, which then starts to break down the polypeptide into smaller amino acid chains. In the intestines, these smaller subunits of amino acids are broken down into amino acids by more enzymes. Once an amino acid it can be absorbed and utilised. Yet again as it is a chemical reaction it needs energy to break down all the bonds along the way. To utilise the amino acid in metabolism you need energy. As with protein and carbohydrates you need bond dissociation energy to digest and metabolise. The bond disassociation energy needed in the metabolism for each macronutrient varies depending on what the needs from that macronutrient is, for example if you need glucose from amino acids compared to if you need amino acids for the immune system, the energy yield will be different.

Still Confused about Calories Enter The laws of thermodynamics?

Enter the laws of thermodynamics. These laws probably drive nutritionists up the wall, because they are hard to grasp in biological systems. We should only be concerned with two laws of thermodynamics and let’s put them in understandable terms for a biological system. The first law states “energy is conserved” meaning energy cannot be destroyed only converted. The second law states (comes into two parts) “heat cannot flow from cold to hot” and “Entropy increases in the universe.” The second law is where it gets slightly tricky for biological systems, Entropy is basically disorder and its opposite is enthalpy, which means order. To create order in the universe disorder cannot be negative. Putting that into practice with the first law goes; you cannot convert one unit of energy into another unit and break even, you will lose some of that energy in heat.


The different macronutrients have different thermic effects, protein is by far the most thermal, followed by carbohydrates and then fats. Thus, eating a slightly higher protein diet will have a different thermal effect and you do not end up with the same amount of energy as say a higher carbohydrate diet. To add to that if you were paying attention to the earlier statement if I am on a high protein, low carbohydrate diet, do not have a readily available store of glucose post digestion? Amino acids can be converted into glucose via the liver in a process called gluconeogenesis and guess what? That involves more chemical reactions and guess what? More energy is needed. All these chemical reactions and differences in the thermal effect of foods show a calorie is not a calorie when applied to a biological system. So “if it fits your macros” in principal is slightly flawed. Because if I have 100 grams of carbohydrates from a highly fibrous source vs say, complete sugar. The digestion of the former will take more chemical reactions than the latter, which will be available instantly. The evidence-based practitioners are silently backtracking to involve these variables in their calorie equations, but on the other hand telling results based consultants that you should make huge Facebook announcements when you are wrong. If your still confused about calories and you’re into your nutrition do a degree in nutritional biochemistry anddon’t waste time going to an uncredited course by uncredited people. In the meantime you can read ‘Biological, Physiological, and Molecular Aspects of Human Nutrition, 4th Addition found here

Hopefully you should be less confused about calories now. Before starting a new diet please make sure you consult with your health practitioner or contact us here


Finley, J.W., Klemann, L.P., Leveille, G.A., Otterburn, M.S., Walchak, C.G. Caloric availability of SALATRIM in rats and humans. J Agric Food Chem. 1994;42:495–499.

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