There are many ridiculous myths in nutrition.
The “calorie myth” is one of the most pervasive… and most damaging.
It is the idea that calories are the most important part of the diet, that the sources of those calories don’t matter.
“A calorie is a calorie IS a calorie,” they say… that it doesn’t matter whether you eat a 100 calories of candy or broccoli, they will have the same effect on your weight.
It is true that all “calories” have the same amount of energy. One dietary Calorie contains 4184 Joules of energy. In that respect, a calorie IS a calorie.
But when it comes to your body, things are not that simple.
The human body is a highly complex biochemical system with elaborate processes that regulate energy balance.
Different foods go through different biochemical pathways, some of which are inefficient and cause energy (calories) to be lost as heat .
Even more important is the fact that different foods and macronutrients have a major effect on the hormones and brain centers that control hunger and eating behavior.
The foods we eat can have a huge impact on the biological processes that govern when, what and how much we eat.
Here are 6 proven examples of why a calorie is NOT a calorie.
1. Fructose vs Glucose
The two main simple sugars in the diet are glucose and fructose.
These two seem almost identical. They have the same chemical formula and weigh the exact same.
But to your body, the two are completely different.
Glucose can be metabolized by all of the body’s tissues, but fructose can only be metabolized by the liver in any significant amount.
Here are a few examples of why glucose calories are NOT the same as fructose calories:
Ghrelin is the “hunger hormone.” It goes up when we’re hungry and down after we’ve eaten. One study shows that fructose leads to higher ghrelin levels (more hunger) than glucose.
Fructose does not stimulate the satiety centers in the brain in the same way as glucose, leading to reduced satiety.
A high consumption of fructose can cause insulin resistance, abdominal fat gain, increased triglycerides, blood sugar and small, dense LDL compared to the exact same number of calories from glucose.
Same number of calories, vastly different effects on hunger, hormones and metabolic health. Because a calorie is not a calorie.
Keep in mind that this applies to fructose from added sugars only, not the fructose from fruit. Fruits also have fiber, water and significant chewing resistance, which mitigate the negative effects of the fructose.
Bottom Line: Even though fructose and glucose have the same chemical formula, fructose has much more negative effects on hormones, appetite and metabolic health.
2. The Thermic Effect of Food
Different foods go through different metabolic pathways.
Some of these pathways are more “efficient” than others.
The more “efficient” a metabolic pathway is, the more of the food energy is used for work and less is dissipated as heat.
The metabolic pathways for protein are less efficient than the metabolic pathways for carbs and fat.
Protein contains 4 calories per gram, but a large part of the protein calories are lost as heat when it is metabolized by the body.
The thermic effect of food is a measure of how much different foods increase energy expenditure, due to the energy required to digest, absorb and metabolize the nutrients.
This is the thermic effect of different macronutrients: