[Leah Deal (OP)]

Hi,
I heard on another PodCast that during the first 20 minutes of a cardiovascular workout, like running, the body is burning off only blood sugar. It is not unitl after the 20 minutes that you start actually burning fat. I don't know if this is true. However, if it is, does that mean that if you run in the morning before eating, that you burn fat sooner, since the blood sugar is probably lower?

I'd love to hear back from you. newbielink:https://www.thenakedscientists.com/podcasts [nonactive]!

Thanks for all your knowledge.
From Minneapolis, MN with regards,

Leah Deal

[Les the Scientist]

I read an interview in men's health magazine that said exactly that.  This guy said that he never ever ate anything before exercising because the body burns it's fat instead of the energy released from the food in his stomach.  So I say it's true !

[thefunkyaquarium]

I've read that as well, in several places.  However, beware that since you're "running on empty", you won't be able to exercise as efficiently as if you ate something before the activity.

My rower friend tells me, you should eat slow-release foods before exercise (e.g. bananas, porridge) and fast-release foods after exercise (e.g. glucose drinks, jaffa cakes) for a fast recovery.

[Leah Deal (OP)]

Thanks! Your remarks are really informative.

Leah Deal

[Edwina Lee]

Aerobics teachers understand when you burn fat and when you don't.

If you exercise too rigorously or too gently, you burn carbohydrate.
Moderate exercise cause you to burn fat. A brisk walk would burn fat nicely.

[Bored chemist]

I'm not sure the body can actually "burn" fat much.
I don't think that muscle cells have the enzymes etc needed to oxidise fatty acids and use the energy produced at anything like the rate they need it when working hard.
They typically consume glucose.
The liver  stores glucose ans glycogen and converts glycogen to glucose as needed.

And, the liver also converts fats to glucose and then glycogen.

So essentially any exercise that uses energy  will draw from the body's stores of glucose, glycogen and fats.
If you don't eat enough calories to replace the stores then the liver will shift fat to compensate.

The rate of exercise is substantially less important than the calories burned.
As far as I'm aware there's no requirement for an aerobics teacher to have any qualifications.

[Edwina Lee]

Aerobic teachers tend to be knowledgeable about metabolic dynamics. Every one I came across (many over the years) has an exercise teaching qualification of some sort. Often they are already in NHS physiotherapy.
Here is an article which supports what I said about using low to medium level of exercise to burn fat.

https://theconversation.com/fat-burning-zone-the-best-way-to-exercise-to-burn-fat-138662

https://us.humankinetics.com/blogs/excerpt/the-bodys-fuel-sources

[Edwina Lee]

I heard on another PodCast that during the first 20 minutes of a cardiovascular workout, like running, the body is burning off only blood sugar. It is not unitl after the 20 minutes that you start actually burning fat.

That makes sense to me. It was what aerobics teachers told us too (more than 17 years ago).

[Bored chemist]

I heard on another PodCast that during the first 20 minutes of a cardiovascular workout, like running, the body is burning off only blood sugar. It is not unitl after the 20 minutes that you start actually burning fat.

That makes sense to me. It was what aerobics teachers told us too (more than 17 years ago).

And what makes sense to me is that the body, having had its glucose stores in the blood and liver  depleted, breaks down fats to replenish them