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A calorie is a calorie, isn't it?

The Calorie Delusion

Wilbur Olin Atwater

Creator of the food calorie count system

The Respiration Calorimeter

  • Calorimetry derives its name from the Latin word calor which means heat.
  • The American chemist Wilbur Olin Atwater, calculated the energy content of various foods by burning small quantities under controlled conditions and then measuring the amount of energy released in the form of heat.
  • By subtracting the amount of energy lost in undigested food found in faecal matter and bound energy in the form of urea, ammonia and organic acids in urine, he was able to determine that carbohydrates and protein provide 4 kcal of energy per gram and that fat provides 9 kcal of energy per gram. 
  • These measurements of metabolisable energy have been used ever since.
  • The values are approximate as there are many biochemical and physiological factors that influence the calorie value of any macronutrient [carbohydrate, fat, protein or alcohol] consumed.

The body is not a furnace - food is digested

  • Food is not incinerated in the body it is digested - the very act of chewing expends energy, the coarseness of the food being consumed can affect glycemic index [GI], and GI can have an impact on hormonal ratios favouring lipogenic vs lipolytic hormones2.
  • In the case of consuming either a doughnut vs. a chicken breast, the doughnut will elicit a surge in the hormone insulin due to the refined sugar and carbohydrate content. The doughnut also has a low thermic effect due to the high fat and low protein content [see below]. In contrast, the chicken breast will elicit a greater glucagon hormone response. This is an important shift in insulin/glucagon ratios as higher insulin levels will signal fat storage and higher glucagon levels will signal glycogen and fat utilization7. The chicken breast will also elicit a higher thermic effect due to the higher protein content.
  • Coarse food may also pass through the gastrointestinal tract [GIT} undigested and calories thus being lost in faecal matter.

  • Every step of the process of extracting energy of food can lower the calorie value of any food being consumed from chewing, to the production of saliva, to the transit of food in the gastrointestinal tract and the mucosal transport of nutrients to tissues and cells, the production of bile in the liver, to the creation of stomach and pancreatic enzymes for the digestive process, the GIT hormone signaling proteins and the cellular process of chemical reactions and energy extraction. All these steps lead to a net energy expenditure that can significantly lower the calorie value of any food being consumed.

The bowel microbiota: How bowel organisms can affect calorie intakes

  • Two main phyla in of bacteria make up 90% of the organisms in the bowel - Bacteroidetes and Firmicutes.
  • "The Firmicutes is the largest bacterial phylum. It contains more than 250 genera, including Lactobacillus, Mycoplasma, Bacillus and Clostridium.5"
  • The importance of these organisms in human obesity is only now becoming apparent.
  • These organisms use dietary fibre predominantly as a source of fuel and can thus lower the caloric value of fibre-rich foods as these organisms take their 'cut' of these ingested calories in the form of fibre.
  • Please view the free NutriDesk tutorial: Bowel Flora
  • "Collectively, the flora has a metabolic activity equal to a virtual organ within an organ3 "
  • "Evidence suggests that the metabolic activities of the gut microbiota facilitate the extraction of calories from ingested dietary substances and help to store these calories in host adipose [fat] tissue for later use. Furthermore, the gut bacterial flora of obese mice and humans include fewer Bacteroidetes and correspondingly more Firmicutes than that of their lean counterparts, suggesting that differences in caloric extraction of ingested food substances may be due to the composition of the gut microbiota6."

The Thermic Effect of Food [TEF]

  • The thermic effect of food or TEF is the increase in energy expenditure above the resting metabolic rate as a result of the energy cost of processing food for storage and use.
  • We must not forget that some of the energy extracted from food is also lost as body heat.
Macronutrient % Thermic Effect
Fat 3%
Carbohydrates 10%
Protein 30%

What does the table above mean?

  • What the table above is actually telling us if we use protein as an example, is that a an amazing 1/3 of the caloric content of the protein consumed will be lost at heat.
  • So if we did the calculations then instead of protein providing 4 kcal of energy per gram of protein, the amount of calories available to the body is 4 x 0.7 = 2.8 calories actually available for the body with 1.2 calories being burnt off as heat.

Let's look at an example of a glazed doughnut vs. a chicken breast7

Doughnut  250 calories Thermic (Heat) Effect
Macronutrient Content Grams Calories

Thermic 'Calories

Fat 11.8 106 3.18
Carbohydrate 33 132 13.2
Protein 33 12 3.6
Total 250 20

Chicken Breast 250 calories Thermic (Heat) Effect
Macronutrient Content Grams Calories

Thermic 'Calories

Fat 10 90 2.7
Carbohydrate 2 8 0.8
Protein 38 152 45.6
Total 250 49

  • Thus the calories available to the body from the doughnut after the thermic loss is taken into consideration is 250 - 20 = 230 calories and from the breast of chicken 250 - 49 = 201 calories left for the body to use.
  • So there are 230 - 201 = 29 calories more for the body to utilize [or have in excess] from the doughnut than from the chicken breast due to the thermic effect of the components and in particular the higher thermic effect of protein.
  • So in reality, the caloric value of food is dependent on the thermic effect of the various macronutrient components, the ratio of Bacteroidetes and Firmicutes organisms in the bowel, how much an individual expends energy to chew their food, how many calories are lost in coarse foods that are passed through the gastrointestinal tract undigested.
  • In the typical carbohydrate-mad Western diet, you are extracting many more calories for storage as fat because of the much lowered thermic effect in comparison to increasing the thermic effect of food by ensuring you have more protein in your meals. So make Every Meal Count by increasing your protein content of each meal eaten.
  • The type of calories consumed as determined by the macronutrient composition of the food consumed, will determine the Insulin/Glucagon ratios after eating and will determine how these calories are dealt with in the body --- fat accumulation or fat metabolism.

Link to Energy Matters References

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References