The commonly accepted scientific explanation of weight gain is one of “calories in” versus “calories out”. It is often referred to as the energy balance equation. The equation reads:
Energy In = Energy Out + Changes in Body Stores.
This is based on the First Law of Thermodynamics which states that energy can be neither created nor destroyed, instead it just changes form.
The “energy in” part of the equation is the energy that comes from the food that you eat, the “calories in”.
The “energy out” part is the “calories out”, the amount of calories that you burn, also known as your Total Metabolic Rate.
The “changes in body stores” are the addition or subtraction of energy in the human body, generally exhibited through increased or decreased stores of body fat and muscle, and to a much smaller degree stored glycogen.
Energy In
The food you eat starts as potential energy and is most often referred to as calories or (kcal).
Unabsorbed Energy
In general, the majority of the food you eat, the calories you ingest, will be accounted for as the food is digested and absorbed by the body. However, food isn’t always digested and absorbed completely. Some nutrients digest and absorb better than others, namely protein. Even among different proteins, there are different levels of absorption. For example, animal proteins absorb better than plant proteins.
The undigested calories don’t just vanish, they can be accounted for: it shows up in your stool. Yes, under the strictest of circumstances, stool can be measured to see how many calories it contains. I have also read that there is research indicating that the amount of bacteria in your gut will influence digestion and absorption rates, though I haven’t examined it myself.
Fiber also adds to this non-absorbed food effect. Since fiber helps to quickly pass food along the digestive track, it will mean that some food doesn’t get digested and absorbed. The undigested nutrients will end up in your stool and thus don’t count towards the “energy in” part.
Energy Out
The “energy out” part of the equation is the most vexing aspect and is most likely to cause mass confusion. Energy out is your metabolism. Since I already wrote about metabolism in my previous post, I won’t go into much detail. Your metabolism consists of your Resting Metabolic Rate, Thermal Effect of Food, Thermal Effect of Activity, and Non-Exercise Adaptive Thermogenesis.
The most important aspect to understand about the “calories out” part of the equation is that it isn’t static. Your metabolism changes due to circumstances. For example, when you diet and start losing weight, your metabolism tends to slow down due to hormonal changes. The fact that your metabolism can change so often, and usually in the wrong direction, can be very frustrating and hard to grasp.
What About Water?
Water is not accounted for in the energy balance equation because water provides no calories. However, water does have weight and water weight can often be responsible for large swings in weight gain or loss. This fact can not be ignored. If you wake up two or three pounds heavier than you were the day before, it’s most likely water weight.
Incidentally, water weight is often what women obsess over. A one pound swing in an undesired direction can often make them question everything they are doing in the gym. The time of the month makes matters even worse, because their hormonal changes may lead them to add a pound or two (or three) of water weight.
Being in, or out, of energy balance
Thinking in terms of weight gain and loss, the calories you eat serve as potential energy as it enters your body:
- If the amount of calories you are eating match the amount of calories that you are burning, your body will be in energy balance. You won’t be adding or losing any body stores (not including water). This doesn’t have to be precise every day. It just has to average out over time.
- If there is too much energy coming in, your body stores increase because your body can’t utilize it all, so it gets stored . Remember, according to the First Law of Thermodynamics, energy can’t be created or destroyed, so it has to go somewhere. In this case, it gets stored as fat, but it can also turn into muscle (in the case of your dietary protein) or stored as glycogen in your muscles. Either way, your body stores increase and you get bigger.
- If there isn’t enough energy coming in, your body stores decrease because the body must borrow from these stores to make up for the lack of energy coming in. Your body must borrow from its stores of body fat, muscle, or glycogen to make up for the lack of energy coming in. What people often don’t realize is that when you lose weight, you aren’t only losing fat. Your body will also burn muscle to meet its energy requirements. This makes it doubly important to keep your protein intake high and lift heavy weights when losing weight. It will help you retain as much muscle as possible.
Conclusion
We may have to add the energy balance equation to politics and religion as topics to avoid in polite company. It seems the energy balance equation is a heated topic, primarily among those involved in the fitness industry and weight conscious individuals.
Some people love its simplicity because it means they don’t have to worry about too many details. On the other hand, some people hate it because it takes a highly emotional and complex subject like weight control and turns it into an unforgiving equation. It leads them to look for reasons that the equation isn’t valid. That’s fine, for that’s what science is all about. A theory has to be able to stand up to scrutiny.
I think there is a lot of resistance to the energy balance equation because it makes everything seem so damn simple.
It doesn’t take into account a myriad of reasons that people eat more than what their bodies can use (or eat too little, some people have trouble gaining weight and muscle- the energy balance equation doesn’t discriminate).
It doesn’t take into account the human experience of emotions, environment, and genetics and the effects they have on appetite regulation and suppression.
It doesn’t take into account that our biology often works against us to maintain our weight and prevent weight loss.
It doesn’t explain why our metabolism slows down or speeds up.
But it’s not supposed to. The energy balance equation simply describes energy transfer within the body.
My feeling is that people look at the energy balance equation through their own prism, through their own experiences with weight gain and loss. The validity of the equation becomes one of personal validation. Either it validates their experience or it doesn’t. It becomes an emotional issue instead of a numerical issue.
Much to the chagrin of human beings everywhere, our lives change. Environment, genetics, hormones, lifestyle, general health, medications, activity level, habits: they all come together to influence our appetite and metabolic rate.
The energy balance equation doesn’t address any of that. That’s the complicated stuff.
The energy balance equation says what it says–and that’s it.
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