Body Fat and Weight Loss
Let’s chat about a tissue type in our human bodies that doesn’t get a lot of positive press on the ‘ol interwebs: adipose tissue. Yup, we’re talking about fat tissue… *Gasp*, *Scream*, *Sigh*... Like it or not, our bodies are actually designed to store excess energy. In fact, we rely on it quite a bit!
We need energy all of the time, not just when we are exercising or intentionally moving. When we are resting, our hearts are still pumping, lungs are still breathing, and brains are still thinking. While we do keep smaller amounts of energy in our liver and muscles as glycogen (long chains of glucose molecules), extra energy is primarily stored in adipose tissue in the form of triglycerides.
This is why having “zero percent body fat” isn’t a thing. Or should we say, *shouldn’t be a thing* because a certain amount of fat is vital for survival! Essential fat is defined as the fat needed to maintain normal physiological functions. In addition to being critical for hormone production, it is found in our muscles, nerve cells, bone marrow, intestines, heart, and liver. Generally speaking, essential fat constitutes about 3% of the total weight in men and 12% in women.
Of course, losing fat that is above and beyond essential fat is normal and healthy if done in a sustainable manner. So how does that happen, exactly? When we are in a caloric deficit, no matter if that is intentional or by accident, our bodies convert fat reserves within the triglyceride molecules into an energy currency that the cells can use. This is done through a very complicated series of metabolic chemical reactions. In a nutshell, here is what is going down:
After approximately 30 to 60 minutes of exercise (this timeline can vary tremendously depending on factors such as genetics, metabolism, fitness adaptations, health, and age), muscle cells run out of available glycogen and must recruit triglycerides from adipose tissue to keep up with energy demand. By breaking down triglycerides into glycerol and fatty acids, these molecules can participate in metabolic pathways known as the citric acid cycle and electron transport chain to yield large amounts of energy. These pathways occur in the mitochondria aka the "powerhouse of the cell." Ah, yes, your favorite organelle from high school Biology class!
The components that are left over and not needed for energy production are then secreted. We call these “the byproducts of fat metabolism” and body ditches them like a bad prom date in a few different ways:
As water: through your skin (when you sweat) and your kidneys (when you urinate).
As carbon dioxide: through your lungs (when you breathe out).
This process repeats itself over and over again anytime we find ourselves in a caloric deficit. Over time, an ongoing caloric deficit leads to noticeable decreases in triglyceride concentrations in adipose tissue thus changes in body composition and/or weight. It is important to note that while the body is accustomed to utilizing fat as fuel, it is still stressful on the body to do so. This is one of the many reasons why a slow, methodical fat loss strategy is recommended.
So there you have it… Body fat is also a friend, not just a foe.
