We had a great discussion after one of our boot camp sessions this week. The conversation was on the topic of where fat goes as we are losing it. It seems to be a very common question and the answer may surprise you.
There are a few old school notions in the world of health and fitness that don't really make sense if you really think it through. For instance the ongoing war about nutrient timing and whether or not you should eat immediately after weight training is often based on a misunderstanding of the body's metabolic process (That is a conversation that we can dive into later). I used to have a very different view before really taking time to look at the science of it all.
The same goes for the whole idea of fat loss. I have spent some time looking at the science and then... you know me, trying to break it down so anyone can understand it. It made me think of the very powerful scene of one of my favorite actresses, Angela Bassett as she is walking away from a car that she just set on fire. The movie came out in 1995, a 21 year old classic. The picture below shows her in all her fierceness. It also is a great depiction of something else.
Quick Science Lesson:
For any fire to burn it needs oxygen. As Ms Basset did the work to set the car on fire, the flames are evidence that some "burning" is taking place. The flame is not the product though. Surprisingly, heat is not the product either. Heat is a property of the flame. The product is the smoke, carbon dioxide and water. Actually, smoke is collateral. It is material that the fire was not hot enough to consume. When the flame is hot enough it burns up everything and the only byproducts are carbon dioxide and water. So, that's it for the science lesson but it is important to understand how fat is metabolized.
In order for body fat to burn oxygen must be present. Most people don't put two and two together to get the real picture of how this takes place. The explanation is actually longer and much more complex. Here is a simplified answer to the question of where body fat goes when you burn it off.
First of all, many people think that excess fat is converted into energy or heat. This is some of that old school "bro science" based off of theories that came about when the whole idea for aerobics was relatively new. the real science was not considered. However, for fat to actually be converted into energy it would violate the "Law of Conservation of Mass" -
Noun1.law of conservation of mass - a fundamental principle of classical physics that matter cannot be created ordestroyed in an isolated system (thefreedictionary.com)
Basically, no matter what happens to mass within a closed system like our bodies It has to be transformed in to an equal amount of the new mass or substance.
So, It is not one of those things where we just get energy (energy, I guess could be considered like the "chemical reaction" that is taking place. the actual burning is the evidence of the chemical reaction. But where does the fat go? Here's where it gets cool.
Much like when a physical fire... that needs oxygen... burns when our body fat is being "burned" it also requires oxygen. And here's what is interesting. The calories (1 kcal = the amount of energy to raise one gram of water one degree) burning = fat burning. The fat burning results in 2 by products. Just like with physical flame. Carbon dioxide and water.
When scientists trace the pathway of carbon dioxide and water from fat loss out of the body they found that out of 10 kg of fat, 8.4 kg are exhaled as carbon dioxide and 1.6 are excreted as urine sweat and tears, the humidity in our breath and other bodily fluids and functions. (British Medical Journal - Read this. Lots of sciencey stuff but interesting)
So - Were does the fat go when you burn it off?
Short answer: You breathe it out.
Sop now we're all "Waiting to Exhale".
Hope that was at least as helpful as it was long. :-)
Coach Scott G Smith