We don’t produce energy, we transform it. And if you are reading this, you are a human being that gets most of your energy from food (unless you are an alien who is into human physiology).
In a nutshell, if we eat more energy than we spend, we store it (weight gain), and if we eat less energy than we spend, we use stored energy(weight loss) - But, we all know that the nutrition game is more complicated than that.
Typically, we quantify the energy stored in food as “Calories”. A calorie is just a unit of heat, 1 calorie represents the amount of heat needed to raise the temperature of 2.2 lbs of water by 1-degree celsius.
The more food you eat, the more energy goes through your body. And different foods have different energy profiles. To put it simply, we usually tell our tribe that carbohydrates and proteins contain 4 calories per gram and that fats contain 9 calories per gram. Well, if you have been tracking calories for a while, you know that sometimes if you hit them perfectly, the calories don't add up in your tracking app. This might explain why:
1 gram of fat: 9.44 cals
1 gram of alcohol: 7.09 cals
1 gram of protein: 5.65 cals
1 gram of starch: 4.18 cals
1 gram of glucose: 3.94 cals
This doesn’t mean, however, that we absorb all the calories that we eat. We will always lose a percentage of what we eat because of factors like GI tract health, age, physical activity, etc. In other words, if we eat 500 calories worth of chicken, we are not absorbing and storing 500 calories.
In addition, the amount of energy that we are recording at the time we are ingesting is not always accurate. 3 ounces of strawberries handpicked in march and 3 ounces of strawberries handpicked in July might contain different properties. That's because the amount of energy in food depends on many factors like:
-Ripeness at times harvest
-Length of storage
-Soil and growing condition
Question: How many calories we need?
This is where our metabolism comes into play. The sum of the following factors tells us how much energy we need, and also make up our metabolism:
1) Basal metabolic rate
Is the least amount of energy needed to survive. Think about just laying in bed without moving a single finger.
2) Resting metabolic rate (RMR)
Is a bit like BMR but it allows for some movement, like digestion, or moving your body around, but still being in a rested state.
3) Thermic effect of food (TEF)
The process of eating food, digesting it, and then absorbing it takes energy.
4) Physical Activity (PA)
All those activities where you are purposefully exerting energy.
5) Non-exercise activity thermogenesis (NEAT)
All activities that are not exercise specifically, but require movement - making your bed, carrying groceries, trying on your computer, etc.
Question: How do we calculate how many calories we need?
Total Daily energy expenditure (TDEE) allows us to calculate how much energy we need on a daily basis. Essentially, we just add up all the calories needed to run the factors that make up your metabolism using the following formula: