Fat Burning Zone

stevencloser

yarwell wrote: »

I'm asking what happens. I'm told the RQ doesn't change, which would suggest the imbalance created during exercise will persist. I'm not talking about EE changing outside of exercise, I was assuming not, but whether a difference in fuelling during exercise is corrected over 24h, and if so how.

If I can burn 20g more fat in the exercise, and do that daily, it's 7.3 kg/year. It's interesting enough in the context of obesity.

All sources I've seen say two things:

• Higher intensity uses up more muscle glycogen than fat, and at rest you're almost exclusively using fat (this, I assume, is regardless how intense, if at all, your exercise is since nowhere I've seen does it state otherwise)
• Glycogen will be replenished the next time you eat carbs

This leads necessarily to the next point which is

• If glycogen gets replenished instead of staying depleted, and you're at a deficit, your deficit will end up being paid for by fat, regardless how much glycogen or fat your exercise used up

stevencloser

This would also mean that the one time where this would not happen is when you're just starting a low carb diet. Your glycogen depletes but can't be replenished completely, you're losing less fat in the beginning until you're depleted to the point at which glycogen use and replenishment equal out.
That one Hall study of carb reduction vs. fat reduction showed as much too I think.

kimny72

smit7633 wrote: »

So I thought the point if exercise was to help create that calorie deficit and to hopefully not loose too much muscle when you're eating less...please advise

Azdak wrote: »

Fuel substrate used during exercise has no effect on loss of body fat. Exercising in "fat burning zone" enhances ability to utilize more fat during exercise which can possibly improve endurance performance, but does not lead to greater loss of fat. Body uses/stores fat on a 24hr/365 day basis--exercise only a tiny part of that. Depending on how much used during exercise, body will up or down regulate fat oxidation the rest of the day. Still depends on calorie deficit.

Conclusion: crap

There are MANY reasons to exercise! In general it is easier to create a calorie deficit with your diet, ie it's easier to eat 200 less calories than to burn off 200 calories. And the best way to preserve muscle while dieting is specifically resistance training. But if you're small and your cal goal is therefore low, exercise can give you a little wiggle room to eat a little more.

But the point of exercise will be different depending on your goals. Different forms of exercise can improve cardiovascular health, increase strength, improve joint health, burn calories, improve your ability to participate in different sports or physical tasks, increase muscle mass, alleviate stress and anxiety, serve as a substitute activity to replace bad habits, assist digestion, provide social interaction, improve mood, there is some evidence that regular exercise can reduce the risk of some cancers, etc...

rankinsect

stevencloser wrote: »

The way our body works, it will always use a mix of fat and glycogen for fuel. The more you exert yourself, the higher the percentage of glycogen, because it's easy to access and just a faster process altogether. So basically, you're burning the most fat percentage wise while you're sleeping, when glycogen is only used to keep your blood sugar steady.
However, of course, during exercise you'll burn more total calories, so there is some point at which, even though you'll burn less fat percentually, the amount of calories from fat you burn peak. That point is somewhere along 60% of your max intensity.

http://sportsscientists.com/2010/01/exercise-and-weight-loss-part-3-fat/

Again however, and they talk about it, it doesn't make you lose fat any faster in the long term, that's still bound by CICO. But they don't say why in that article I think.

The why is easy. Even if you train up to an intensity where you're almost exclusively using glycogen for fuel, later on during your next meal(s) that glycogen will be replenished by carbs from your meal(s) because the body tries to keep glycogen levels up for intense exercise like the one you just did and for your blood sugar levels.
http://www.ncbi.nlm.nih.gov/books/NBK21190/

Those carbs that are used to replenish your glycogen are then obviously not available for fuel, your current deficit is increased from that and you're losing fat because you're at rest. So while you didn't burn much fat during exercise, you're burning extra afterwards. It's like you delayed the fat loss from during the exercise to the rest time afterwards.


Maybe an example helps illustrate that.

Let's say your normal daily burn is 2000, your exercise burned 500 at 100% glycogen use.
That means your glycogen stores are down by 500 calories, you lost no fat so far.
You're eating 2000 calories that day, you're at -500 calories but all of those were from glycogen, oh noes!
But, 500 of those 2000 calories you ate go to replenishing your glycogen stores, it's "paying" for your exercise so to speak, and the other 1500 go to your normal burns and you end up at -500 calories that are going to be taken from mostly fat.

That's simplified of course.


Tl;dr: It's another biological fact that gets widely misrepresented by the diet industry.

Yup, basically came to say that, but you beat me to it. It's a lot like discussing insulin response to high carb meals - on an hour by hour basis, the effects are real, but on longer time frames there is no effect - it comes down to the cumulative deficit over that time.

Azdak

yarwell wrote: »

Azdak wrote: »

yarwell wrote: »

Azdak wrote: »

Fuel substrate used during exercise has no effect on loss of body fat.

Do you have any evidence for that ?

Saw this earlier, which sounded relevant : smile:

"For over 20 years, we at [redacted] have seen this all too often, particularly with women. Many of these ladies are on a vigorous aerobic exercise routine (spinning classes, running, cycling or swimming) and they are VERY committed to their program. Yet when they finish their daily exercise they more than likely eat a lot of carbohydrates and they even may be told by a trainer to eat a lot of “good carbs” to keep their glycogen charged which will ensure a great workout. To continue to do this and expect to have great weight loss success is folly as we are just replenishing the glycogen that we burnt during exercise. "

Sounds like the back half of many marathons and fun runs.

No I just made it up for fun.

Of course I do:

Look up Melanson et al. Exercise improves fat metabolism in muscle but does not
increase 24-h fat oxidation

Title pretty much says it all.

Review :-(

How about a metabolic study that shows the difference over 24h or longer from exercising at two different intensities with equivalent energy expenditure that burn a different amount of fat.

If I can burn 20g more fat in the exercise, what's the mechanism for that getting corrected over the day ?

In the review linked they say typically say "24-h RQ did not significantly differ" but in general this looks to be more due to underpowered experiments. In the graph below they show significant differences in carb oxidation, which should be reflected by differences in fat oxidation if the experiment is steady state ie in balance over the 24h. Otherwise the glycogen depletion would accumulate and the response would change.

The review also has statements like "Fat balance was also not affected by exercise (−4 ± 10 vs. 26 ± 10 g)." which I struggle with. If I was to lose $4 or gain $26 would I say it was the same ;-)

The article link I sent has the study you requested included in the review.