Having thoroughly covered the difference between weight loss and fat loss and the importance of body composition, I would now like to build upon our discussion and talk about calories and energy balance given that these two topics are 1) widely misinterpreted, and 2) intimately involved in driving changes in body weight/composition—contrary to what some try to argue. Indeed, it is not hard to find claims that calories do not matter when it comes to weight gain or weight loss (and that other things such as hormones or just one single hormone is all that matters). This, however, is simply not an honest interpretation of the literature as will become evident shortly.
Because this is such a hefty topic, I will split it up into two parts (possibly three if needed). In Part 1 (today) I will cover the topic of energy and calories and begin to explain energy balance, at least from the energy intake side of the equation. In Part 2 I will explicitly cover energy expenditure and how measure it, as well as how the energy balance equation changes in response to a variety of conditions (e.g. meal frequency, macronutrient composition, overfeeding and underfeeding) and the implication of such changes—it is here that I may need to break it up into three parts. (TBD!)
The main point in all of this is that calories do matter, energy balance is a thing, and all of it is more complicated than you realized or heard from some Instagram influencer.
Let us begin with the basics.
Energy is simply the capacity to do something—i.e. work. In your body, that means keeping you alive by maintaining ion gradients, building new macromolecules, allowing for locomotion, and so on and so forth. Should you stop doing any of this, you will die. (The fancy term is thermodynamic equilibrium.) Since energy cannot be created out of thin air, you need to obtain it (i.e. transfer it) from some other source—that source being food. Simply put, food contains energy, so we put that food in our mouths and chemically digest it so that we can transfer the energy it contains (within its molecules) into the bonds of ATP (the universal cellular energy currency) that our cells constantly make that allows us to do work and stay alive.
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