Fasted Cardio: Morning date with Death or Destiny?
Fasted cardio, those 2 little words spike all kinds of mixed feelings through my body. Cardio for most is a struggle, try adding an earlier wake up time and lack of food to get your motor started and you will think you just entered the fast track to crazy town. I have spent many weeks second-triple-and quadruple guessing my current prep to my last one and why would I need to be including so many more early AM sessions this time around than last? It’s easy to get caught up in the silly gym stigmas like “go ahead if you just want to burn your hard earned muscles off” or “exercising with no fuel=waste of time”. It was honestly actually easier to just jump in with the crowd and dismiss fasted cardio like it was the fitness plague, than actually learn what it might have to offer. Instead of following suit and fighting what could possibly be a “good thing”, I decided to face the pavement and get to the bottom of the widely debated topic.
What exactly is fasted cardio?
Many people think fasted cardio is simply training on an “empty stomach,” which they usually think is simply a stomach that “feels empty.” Well, they’re wrong! Fasted cardio is cardio done while in a “fasted” state, wherein your stomach is empty, but there’s a bit more to it than that.
When you eat food, it gets broken down into various molecules that your cells can use, and these molecules are released into your blood. Insulin is released as well, and its job is to shuttle these molecules into cells. Depending on how much food you eat in a meal, your insulin levels can remain elevated for several hours (anywhere from 3 – 6+). When your body is digesting and absorbing what you’ve eaten, your body is in a “fed” state. Once it has finished processing and absorbing the nutrients, insulin levels drop to a “minimum” low, and your body enters a “fasted” state. Every day your body moves between “fed” and “fasted’ states. 
Some simple facts to keep in mind…
- Fat oxidation happens at a faster rate when insulin is low.
- Insulin levels are influenced by blood glucose, and blood glucose is lowest when we haven’t eaten in a while (especially in the morning).
- Low-to-moderate intensity activity predominantly utilizes fatty acids as an energy substrate, especially during longer durations of activity (45-60 mins).
You will be more than glad to know fasted cardio isn’t for everyone, but it is GREAT for athletes with body fat levels in the low single digits males (5-6 percent) and females with body fat in the low teens (13-14 percent, That’s ME!), especially if they have specific problem areas like the lower back or thighs. Research has shown that high-intensity interval cardio is particularly good for getting rid of stubborn abdominal fat, including dangerous accumulations of visceral fat.
Some studies have found that exercising in glycogen depleted state a fasted session can burn almost 20 percent more fat compared to exercising with fuel in the tank. Why? Once we eat, insulin (which regulates the breakdown of fat) increases in our body. And, according to some research, higher insulin levels have been shown to suppress fat metabolism by up to 22 percent. The hope is to teach their body to adapt to low blood sugar levels by burning fat and, as a result, prevent “bonking” during high activity.
Depending on what style of training you incorporate into your fasted cardio will produce different results.
What type of Cardio is BEST?
HIIT is where the money is at! I like to make my time count and not spend endless hours of my day slaving on a stairmaster. Keeping your cardio sessions shorter means you better preserve your muscle and strength. This is especially relevant to fasted cardio as it accelerates muscle degradation, and the longer you train in a fasted state, the more muscle you lose. If you’re a competitor like myself, you will do anything to save those hard-earned muscle fibers.
All that said, some people say HIIT performed in a fasted state is silly because fat oxidation rates are much lower during HIIT exercise. Well, while it’s true that fat oxidation rates decline as cardio intensity increases (as glycogen then becomes the fuel of choice), there’s more to consider. Reseach has shown that as you continue to perform regular high-intensity interval cardio sessions, your muscles “learn” to use less glycogen during workouts (thus increasing fat oxidation rates during the workouts), and your muscle cells also get better and better at oxidizing fats. This latter point is particularly relevant to fasted training as, over time, high-intensity interval training increases the total amount of fatty acides your body is able to metabolize during workouts. The actual amount of additional calories burned due to HIIT’s greater “afterburn” effect will probably never be more than 50 to 80, but hey, that adds up over time.
And the final MOST IMPORTANT element to pair with your fasted cardio…
Branched-Chain Amino Acids or Leucine
All you need to take is 10g of BCAA’s or 5g Leucine approximately 10-15 minutes before/during exercise. This suppresses muscle breakdown during your workout with a minimal impact on insulin levels, much lower than whey protein. 
Article Contributed by: Biancha Foust NPC Competitor and Axis Labs Athlete