AM cardio on empty is good. I know the rationale behind this. But as I read more extensively, as with everything pertaining to science, there is always a conflicting view. It's good mainly because it facilitates fat utilization because of the fasting state (depletion) through the night. But because cortisol levels are highest during a sleep stage, doesn't AM cardio on an empty stomach increase catabolism even though resistance training is absent? Wouldn't it be better to have some protein/fat? I know that is an option too, but what's happening re: catabolism during AM empty-stomach cardio?

It is very common for bodybuilders/fitness people to do AM pre-meal cardio. In general it is a successful stategy. But as you said there are always different opinions and.... Opinions are like noses, everybody has one.

The theory is that your body will be in a state in which fat stores can be easily used for energy at this time. I don't think anyone would disagree with this; however, I'm not sure how much it really matters.

From a calorie perspective everything should equal out no matter what time you do the cardio. From the glycogen or fat perspective... if you use glycogen during the cardio it will eventually encourage your body to use more fat later via the calorie deficit. From the muscle catabolism perspective... a relatively short cardio session (15-30 mins) should not hurt too much.

Also on a LC / insulin controled WOE timeing of cardio is probably less important than for the general population. We would burn primarily fat regardless.

So... if you overdo cardio, catabolism could be an issue. If you don't overdo it, it should not be an issue. When you do it is really a matter of preference.

That pretty much summarizes my feelings on the matter. I hope it helps.

As always, a really great post MPS.

mps, very interesting comments. Especially the point about LC, I would bet that most of the studies about how much fat is burned on an empty stomach are most likely done on people who eat more carbs. Thus the effect of morning excercise on an empty stomach might not be that different than if one did eat before since LC people are already burning fat as the major component.

I have long suspected as much.

My specific concern is cortisol levels at that time of the morning.

Is that really true for women? It's pretty hard to gain muscle in women due to our testosterone levels being so low. And cortisol seems to be the main hormone of concern to women when it comes to catabolism. So shouldn't women then do as much as possible to limit catabolism, however little?

btw I think cortisol is less brutal to muscle in women than men, but still a concern.

Hmmmm - interesting notion.
On the one hand, we have less muscle, so cortisol could be MORE of a problem, theoretically, because we have so little muscle to begin with. On the other hand, belly fat is often cortisol fat, and this is more often seen on men.

Hmmmmmmm.....I'm intrigued...

I have very low energy levels in the morning, so it is not an issue for me.

I side on the camp which seeks to end the night fast ASAP and eat food first thing to stop catabolism. Then exercise any time during the day. 24 calorie balance is more important that what percentage of fat vs. glycogen you are burning.

It is kind of like the cardio fat burning zone. I mean, who cares if you are burning 80% fat or 20% fat? It is just calories.