I've only read anecdotal stuff on this subject, but the carb v.s. fat preference seems to at least partly pace related.

Since fats are much lighter than carbs per calorie, where is the pace threshhold for preference of one over the other?

Edited by asandh on 07/13/2010 01:19:42 MDT.

Only 3 mph. That's on the most rock laden trail in the U.S.
You have to think about were you are going to place your foot on almost evry single step.
This takes a huge toll on the over-all speed.

Michael was averaging 3.1 mph the whole time and 2.6 over-all before his crash.

As far as the Hammer Jel, I completely agree.
I used H/J and Jels on the TRT and it was way too heavy. For what should be 5-6 pounds of food came in over 8.

I have the hardest time eating on the run after just abut 12 hours in on a trrail.
I have to stop every time I go to eat something.
If I use the H/J for about 50% of my calories, I only need to stop for half that time.
This makes it worth the extra weight for me.

If I didn't have that problem, I would only use it the first 12 hours to make way for the heavier caloric food.

Art,
No specifics here, but a lot depends on your level of fittness.

I believe I saw a note that world class women marathoners can reach 50% fat metabolism! I'd be luck to get 10% at that level of effort.

Also, The Arctic 1000 Team specifically trained to increase fat metabolism, and tried to keep their pace appropriate to that. If I recall, Richard Nisley was involved with that.

Bottom line: A lot of science, training, note taking, and discipline.

my main question is at what intensity level can fats be used instead of carbs to cut weight.

Edited by asandh on 07/13/2010 01:21:08 MDT.

As I've mentioned in the past, the latter part of my training and JMT recon hikes were done with Hammer gel but I swapped it for a 80% snickers 20% gel diet at the last minute to reduce the pack wait a few pounds. Furthermore, I used the gel on the pass ascents and saved the snickers for the lower intensity sections. I thought I'd be safe with this level of carb/fat but I'm guessing I wasn't at the level of exertion I was operating at which contributed to the meltdown.

So now i'm planning on consuming 18k cal of perpetuem and 3k of recoverite. this translates to 250 cal per hour for 3.5 days. this is roughly the level of caloric consumption i've done for every hike. i want to bring as many calories as i can consume because i expect to exhaust all body fat before the end. I'm trying to gain 5 lbs of fat before the next attempt but my metabolism is jacked up so high right now this probably isn't going to happen. i also started training with perpetuem (but switched to gel for logistical reasons) and never had a problem with it while i was using it. The longest hike i did with perpetuem was 53 miles and had no problems. I have noticed that the perpetuem seems more satisfying than the gel. I always felt a bit hungry with the gel at 250 cal per hour but i guess the fat/protein in the perpetuem made it more filling.

So the difference now with the perpetuem is that i want to basically consume it like a gel by mixing it into a concentrated syrup--because my hydration source is a separate camel bag. The perpetuem syrup is disgusting but i hope this will be fixed by flavorizing it myself to my liking with emergen-c.

I couldn't agree more with Aaron's comments about rocks. During rocky sections virtually all of my concentration is focused on the rocks and optimizing where I put my feet to minimize wear and tear and potential injuries. A 'nice' benefit of this though is you become unaware of the passage of time...

"So my main question is at what intensity level can fats be used instead of carbs to cut weight."

Art,

Fat will be metabolized at any level of exercise up to the anaerobic threshold. It is a question of what percentage of
the required energy will be supplied by fat at any given level of exercise. The slower the pace, the higher the percentage of energy supplied by metabolizing fat.

Art, it seems like you are trying to save weight in lieu of speed. The post by Tom sums it up nicely and there's not much to add to it.

The only thing is that you don't need to supplement with lots of fat, your body (and mine, and his, anybody's) has more than enough energy to run across United States on fat reserves alone. You just need to go slow enough. But more faster you go, more carbs you need. 3 mph is a good average for JMT and it's not slow enough to warrant a high fat diet. Be careful.

Tom said "The slower the pace, the higher the percentage of energy supplied by metabolizing fat."

It's not the slow pace that affects utilization, it's the pace relative to your anaerobic threshold. The more "spare" oxygen you have, the more fat you can metabolize.

The better trained you are - the faster you can go while remaining below your anaerobic threshold - the more you will be able to utilize stored fats.