Depleting Glycogen storage before fat burning, or not?

[Julian_M]

In exercise and workout for the purpose of losing weight. Isn't it that the glycogen in the liver takes 20 hours to deplete. Must one deplete glycogen storage first before fat burning in cells would be utilized? But I read conflicting reports that even without depleting glycogen storage, fats burning can happened. I need to understand the exact biological mechanism for this where fat burning occurs even when glycogen in liver is still there. Thank you.

 

[berkeman]

In exercise and workout for the purpose of losing weight. Isn't it that the glycogen in the liver takes 20 hours to deplete. Must one deplete glycogen storage first before fat burning in cells would be utilized? But I read conflicting reports that even without depleting glycogen storage, fats burning can happened. I need to understand the exact biological mechanism for this where fat burning occurs even when glycogen in liver is still there. Thank you.

This is a technical forum at PF, so you are required to post mainstream/valid links to what you have been reading on your question.

 

[Julian_M]

This is a technical forum at PF, so you are required to post mainstream/valid links to what you have been reading on your question.

This is a common questions in the mainstream. I just want to understand the exact chemical pathways. I read this for example:



Someone asked: "Do you really need to "deplete glycogen stores" in order to burn fat at all?".

Someone answered:

"Let's get something clear. 95% of the people in ANY weight loss sub, not just keto, have no freaking clue what they're doing.

No, you don't need to deplete glycogen stores to burn fat. Fat burning (lipolysis) AND glucose burning (glycolysis) happen simultaneously throughout the day, even in people not in a caloric deficit.

The rates of each of these energy mechanisms varies based on many factors, including energy level (lower energy = more lipolysis), hormone levels (higher insulin, more glycolysis, higher glucagon, more lipolysis), activity levels (high intensity, quick = glycolysis), what you're eating (more carbs, more glycolysis), etc.

If you DO deplete your glycogen stores, you leave your body no choice but to burn fat and the glucose it can produce via gluconeogenesis, which is really just enough for your brain, RBCs and a few other things.

But as others have said, you can lose fat on any type of diet. You can lose fat on Hershey bars if you want. Hopefully your goal is to do more than lose fat though."


Is it true? Need medical references about it or the chemical pathways involved why fat burning can occur even when glycogen stores are not depleted.

 

[jrmichler]

Get a copy of Lore of Running 4th Edition, by Tim Noakes, MD. The answer to your question is in there, although you will need to spend some time digging. If not in the text, the list of references runs about 100 pages. Sample from page 107 (MUCH more in the text):

 

[Julian_M]

Get a copy of Lore of Running 4th Edition, by Tim Noakes, MD. The answer to your question is in there, although you will need to spend some time digging. If not in the text, the list of references runs about 100 pages. Sample from page 107 (MUCH more in the text):
View attachment 371015

My question was whether fat burning can occur before glycogen stores got depleted? Any other reference that directly address it? The book Lore of Running is about running. I simply want to know if one walks for 2 hours a day and not run, whether fat burning can occur if the liver glycogen is still not 0%.

 

[jrmichler]

The ratio of fat versus glycogen burning is a function of exercise intensity, duration, aerobic fitness, diet, and other variables. The chemistry is similar for running, walking, swimming, cross country skiing, or other exercise. It's all covered in the book.

 

[berkeman]

My question was whether fat burning can occur before glycogen stores got depleted? Any other reference that directly address it? The book Lore of Running is about running. I simply want to know if one walks for 2 hours a day and not run, whether fat burning can occur if the liver glycogen is still not 0%.

The ratio of fat versus glycogen burning is a function of exercise intensity, duration, aerobic fitness, diet, and other variables. The chemistry is similar for running, walking, swimming, cross country skiing, or other exercise. It's all covered in the book.

@Julian_M -- after you get the book and read it thoroughly, DM me if you want this thread reopened. For now the reference given should answer your questions, so this thread is closed for now.