Question

Why doesn't your body use calories in the same way. Explain why this is true.

Answer 1

Of all the nutrition myths, the calorie myth is one of the most pervasive and most damaging.
It’s the idea that calories are the most important part of the diet — that the sources of these 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’s true that all calories have the same amount of energy. One dietary calorie contains 4,184 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

Here are 6 examples that prove a calorie
is not just a calorie:

Even though fructose and glucose provide the same number of calories, fructose has far more negative effects on hormones, appetite and metabolic health.
Protein calories are less fattening than calories from carbs and fat, because protein takes more energy to metabolize. Whole foods also require more energy to digest than processed foods.
Increased protein can lead to drastically reduced appetite and cause automatic weight loss without the need for calorie counting or portion control.
Different foods have different effects on satiety and how many calories you end up consuming in subsequent meals. This is measured on a scale called the satiety index.
Low-carb diets consistently lead to more weight loss than low-fat diets, even when calories are matched between groups.
Studies show that refined carbohydrates lead to faster and bigger spikes in blood sugar, which leads to cravings and increased food intake.

However the bottom line is :

Different calorie sources can have vastly different effects on hunger, hormones, enrgy expenditure and the brain regions that control food intake.
Even though calories are important, counting them or even being consciously aware of them is not at all necessary to lose weight.
In many cases, simple changes in food selection can lead to the same or better results than restricting your calorie intake.