Fats vs Carbs: How Our Bodies Store Energy

Energy Substrate Utilization: Fat vs Carbs

    We have two primary forms of energy substrate in our body, and a few ways to store that energy! 

Fat -

we usually think of this as body fat, but we have several different types of fat. However, for the purpose of this discussion we will be mostly referring to subcutaneous body fat.

Fat Oxidation is the process of “burning” fat for energy. We store body fat in our body in a few ways, but the most important part to consider here is that we have a tank that never fills up. It’s like the Mary Poppins bag of energy storage. There’s no end to it. We can store fat infinitely, and just keep stock piling that storage. 

Carbs -

All carbs break down into glucose, we store glucose in our body multiple ways too! Here are 3 of them:

1. Blood Glucose - keeping everything running normally, supplying your brain with fuel, etc. Our bodies keep this in a very limited range, when it gets too high, in a properly functioning system, our body starts to store this glucose so "blood sugar" levels stay in normal, healthy ranges. So we have limited storage because if it gets too high, it's dangerous and causes problems overtime. Our body will not let it stay out of range. 

2. Muscle Glycogen - This is glucose that has been taken into our muscles and stored there. Our body will use it when we need it, which is usually because we are moving our bodies and our muscles need fuel. This is different than when our blood sugar gets too low. We have limited amount of glycogen storage in our muscles.

3. Liver Glycogen - This is glucose that is converted to storage in our liver. It is stored and released in response to blood sugar levels, but like your car's gas tank, it can only store so much. Once the tank is full, it’s full.


To give you an idea of HOW MUCH of these energy sources we can store - here is an example of a common ratio of Fat storage vs Glucose storage.



Our body preferentially burns through our glucose first, because, without getting too detailed, it’s easier on our energy systems. It's faster and "cheaper" for our body to use glucose. It's the McDonald's of energy sources. Cheap, fast, easy. That’s just how we are put together. So, if you want to access those thousands of calories of FAT storage, we have to make sure we don’t constantly have sugar to run on instead. The best way to do that is to systematically control and vary our carbohydrate intake, in response to when we need it most.

The fact of the matter is, we have infinite fat storage, and relatively little carb storage, so the good news is, we can push our bodies into using fat as fuel with a little strategic timing. If you are consistently burning through your glucose stores, and consequently then switching into burning fat, your body gets better and better at it. We become “fat adapted” and that leads to not only burning body fat easier, but less blood sugar related mood swings, cravings, and dependency on sugar and eating every few hours. Our bodies are designed to withstand a little hunger here and there, without major consequence, but because we are so used to eating frequently and relying on incoming glucose to keep us going, we rarely give our bodies the chance to access our body fat storage and burn the “extra” calories we have! When it comes to burning fat, we really just have to give our bodies a chance.

About Ashley:

Ashley is a Pilates instructor and entrepreneur in NYC who specializes in biomechanics and exercise nutrition for women. She uses the science behind exercise physiology to empower her clients to lead healthy, happy lives. Her passion project is writing “The LEAN Life Newsletter” which goes out every Tuesday and focuses on Lifestyle, Exercise, Active recovery, and Nutrition and serves as the backbone for her L.E.A.N. Life online health and fitness programs. She aims to get this information into the hands of as many women as possible so they can feel stronger and more confident in their bodies. For more information head to AshleyBrownPilates.com or @AshleyBrownPilates on instagram, or click here to get on the L.E.A.N. Life List!