Cardio - how long until fat is primary fuel?

[Vidiot]

At a pretty good intensity of steady cardio, e.g running, how long until your body uses fat as primary fuel? First we use stored glycogen correct?

I'm asking this because I can only do my cardio in the evenings around 9pm and by then I've been eating all day (duh). I'm worried that if I run for 30 mins my body might only be burning fat for the last 10 minutes or something.

Somewhat related question: if you're on a lowish carb diet then there isn't as much stored glycogen and your body will go straight to fat right?

Thanks!

[Wowzer]

At a pretty good intensity of steady cardio, e.g running, how long until your body uses fat as primary fuel? First we use stored glycogen correct?

I'm asking this because I can only do my cardio in the evenings around 9pm and by then I've been eating all day (duh). I'm worried that if I run for 30 mins my body might only be burning fat for the last 10 minutes or something.

Somewhat related question: if you're on a lowish carb diet then there isn't as much stored glycogen and your body will go straight to fat right?

Thanks!

Depending on intensity, you will reach max fat burning for that intensity when you reach 'steady state'. That usually takes about 3-5 minutes.

However, I wouldn't be concerned. It makes little difference what is used as a fuel source. What is important for fat loss is calorie deficit.

[dcairborne]

To answer your question. At what point does the body start buring fat as its fuel source? This can be all day long depending on your diet, not just during cardio. This question can only be answered with knowing your diet for the entire day, and the meal that came before your cardio session. If you are on a carb restricted diet, where you empliment a carb cut off time (you only eat your desired daily carb amount before a certain time of day), then your body should be converting fat as its fuel source for a good part of each day, including your cardio sessions. This process is known as Ketosis, a state were the body produces an abundance of keton bodies which break down fatty acids as the bodies primary fuel source. The fat is then released through your urine and when you exhale. So your answer could vary depending on carb intake and at which time you eat those carbs. Pro's/Con's to all diets so a Ketosis diet might be worth looking into if you are concerned with your body burning fat as its primary food source. Let me know if this helped at all?!

[mpipes]

Don't worry about it. The miniscule amount of fat you burn directly through exercise is pretty insignificant.

The other 23 hours of the day have far more impact on your fat loss than the 30 minutes of cardio.

[KowboysUp]

This is something I never understood about people's thinking around cardio:

If you weren't going to use that glycogen as fuel unless you had run (lets just presume not), doesn't that mean that AFTER the glycogen is gone, your body would THEN start burning fat instead of the glycogen it would have been burning? Is this not exactly what we're looking for?

In other words, whether or not you're burning fat, you needed to get through that glycogen to drop fat one way or another.

I don't see how this could not be true, and I never understood the mysticism around "fat burning zones". It's all about creating a deficit, and cardio does that wonderfully.

[obesebeast]

the fat burning zone is only speaking in terms of dietary fat, your dietary fat cannot be oxidized as much during anaerobic exercise.

and never question if you're ketotic or not after a long cardio session, the average male has over 4000 cals of glycogen stored in the muscles/liver and it will take days of low carb and high intensity exercise to actually become ketotic and even then, you don't burn more "fat" than you would on a traditional diet at the same calorie deficit.

the world is a giant energy equation and the body is extremely efficient at extracting calories from foods consumed, ~95% regardless of amount consumed. If you consume 2000 cals in that day and burn 4000, your body is forced to find calories from somewhere else, aka itself. If you at 20% bf @ 200lbs, thats 40lbs of fat, ~30lbs of it can be used to fill this deficit 1lb of fat is 28g x 16oz x 9 cals = 4032 cals per 1lb fat . So 30lbs x 4032 cals. 120,000+ calories stored.

no need to reinvent the wheel, just eat less and move more and let the laws of physics take its course.