DISCLAIMER: The following information is general information. Do not use it in place of an actual doctor or dietitian. This article is aimed at otherwise healthy individuals who have a typically functioning metabolism. If you think you have something genuinely wrong with your metabolism, consult a doctor. The scope of this article is to simply draw back the curtains a bit to look at the science under-girding weight manipulation.
Here is the basic rundown. Your body burns through a set amount of calories every day to just keep you living. This is called non-exercise activity thermogenesis… which basically means “everything you do that is not considered exercise.” This ranges from the way you wave your hands while you talk to how often you pick your nose and everything in between. This is why habitually taking the stairs instead of the elevator makes a difference. This will be abbreviated as NEAT. You can also Google NEAT and get a million other summaries of it.
NEAT is part of a larger system. That larger system is how your body effectively balances the energy you take in throughout the day. This energy, as described at the very beginning, is calories.
What is a “calorie”?
It’s incredibly important to break here and understand what a calorie is. Calories are not some ethereal, abstract concept. They are a measurement of energy. Specifically, it is the amount of energy needed to raise the temperature of 1 gram of water, sitting in a space with the pressure of 1 standard atmosphere, 1 degree Celsius.** (More on the calorie here)
How are calories in food measured?
You might be thinking, “but what does heating water have to do with what I’m eating?” As a direct correlation, absolutely nothing. However, there is one way to find out how much energy your food has with reference to heating water. I present to you, the Atwater System. The short version is this: put your food in a sphere that has an endless supply of oxygen. Surround that sphere with water, and be at around sea level. Now literally light your food on fire, let it burn to ashes, and calculate the heat of the water afterwards. You have now calculated the amount of energy in your food.***
What does energy have to do with body weight?
This is crucially significant because now we can related it to a fundamental law of the universe: energy cannot be created nor destroyed.**** This means that energy has to become something else. In other words, the energy from your food will always retain its energy, albeit in different forms (heat, waste, fat, muscle, etc). This is where the concept of weight manipulation becomes front and center. If you have excess energy, that energy will become fat, muscle, either, or both. Similarly, if you aren’t taking in enough energy to maintain the biological processes carried out by your body, your body will then break down fat and muscle to fuel itself.
Conceptualizing Energy in the Body
Now that we have a grasp on what a calorie is, it now might be helpful to think of energy in terms of its forms.
One (pound) box of fat (tissue) = 3500 calories
One (pound) box of muscle (tissue) = 700 calories
One (gram) box of fat (macronutrient) = 9 calories
One (gram) box of carb (macronutrient) = 4 calories
One (gram) box of protein (macronutrient) = 4 calories
One gram of alcohol = 7 calories
How does the body change with energy input/output?
For every 3500 calories that your body is in a surplus, that means you’re eating more calories than you’re burning, your body will store it as 1 pound of fat. For every 3500 calories that your body is in a deficit, that means your eating less calories than you’re burning, your body will burn 1 pound of fat as fuel. So you can think of it as a surplus is storing up energy for future use, whereas a deficit is tapping into stored up energy (body-fat) and using that to make up the difference. This relationship is referred to as CICO – Calories in : Calories out. All of weight loss comes down to this relationship. There’s much to be said about the nature of muscle loss and muscle gain, but I’ll keep it short here: muscle needs calories to be created, but muscle cannot be force-fed. The body creates muscle in response to stimulus (lifting weights for example), and will create muscle as it deems it necessary. Thus, if you eat at a GIANT surplus, you will just get fat and not get tons of muscle. This relates also to homeostasis, but is ultimately beyond the scope of this article.
Starvation Mode: What’s going on?
With all of that out of the way, let’s clear the air a bit. If “calorie” is a description of energy, then we can assume it functions in the same way all energy does. Like a car uses gas for energy, some uses can be more or less efficient. Some cars get 60 miles per gallon, others get 6 miles per gallon, and these all have numerous variables which determine the efficiency. Here is something that never happens: when you get low on gas, your car will never turn on an efficiency mode that turns gas usage into more gas storage. I have never, not once in my life, seen my gas meter go up after hitting empty except when I put gas in myself. The body is the same way – if you starve it, it may get more efficient (or cut processes it deems unnecessary), but it’s still starving and withering away. People suffering from lack of food do not get fat because it is physically impossible. Their body may get more efficient at using that stores it has (this is largely what NEAT is responsible for), but it will never generate energy ex nihilo.
This concept of increasing efficiency is something to be aware of when dieting. The body adapts to stress, and losing weight is itself a type of stress. The amount of calories a body needs to survive also depends on how much “body” there is, so naturally the more you lose, the less calories it takes to keep you alive. Simultaneously, the body is also trying to adapt by reducing its NEAT. So not only does the body require less calories, but your body is also trying to preserve itself by reducing general activity levels. This can be worked through by forcing yourself to go for daily walks. Similarly, if you’re trying to gain weight, the body will attempt to increase your NEAT as to expend all of the excess energy it is receiving. This is the crude explanation of homeostasis. The mechanics of it are, as previously mentioned, out of the scope of this article.
To summarize – your body has a daily maintenance level of calories. In order to to either lose weight or gain weight, we must either eat less or more calories than the total energy our body expends. This concept is called Calories in : Calories out, or CICO. Learn how many calories you expend per day, then manipulate the amount you eat to get the results you want. Combine with diligent training and you’ll be well on your way to changing your body.