Subscribe Contribute Advertise Facebook Twitter Instagram Forums Newsletter
Turning fat into fuel
Display Avatars Sort By:
Dan Johnson

Locale: PNW
Turning fat into fuel on 12/30/2012 21:46:33 MST Print View

So does (or has) anyone tried to transition from fueling by sugars to fueling by fats? I've been reading more how someone can (re)train their body to move at a slower heart rate to burn more fat than sugars resulting in not needing as much food to have been ate on the trail.

I'm looking at doing a 40 mile run/hike (in 12 hrs) this upcoming summer and I'm not liking the fact that my pack will be full of so much food (fuel).

Anyone have any insight?

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Turning fat into fuel on 12/30/2012 22:12:29 MST Print View

The percentage of carbs utilized closely follows what percent of your VO2 max you are operating at.

At 80% of VO2 max you will need about 80% of your fuel to come from carbs (maltodextrin or bars).

If at 80% VO2 max you are currently moving at 4 miles per hour you goal would be to improve your conditioning to accomplish that at 60% VO2 max, thereby reducing you need for carbs.

Having said all that, 12 hours times 300 calories per hour comes to 3600 calories, and 36 ounces HammerGel would get the job done. Or mix maltodextrin powder along the way for a lighter solution. (Greg G. will chime in here soon.) Or any high density phood.

You'll be burning more than 300 calories per hour, but that is about all you will be able to metabolize. Also, you should be starting the event with about 1500 calories of stored glycogen "in the bank". Add to this fat utilization and all is good.

Don't forget the hydration and electrolyte components. They matter a Lot.

Hiking Malto
(gg-man) - F
My latest ah-ha on 12/31/2012 06:10:44 MST Print View

I often do very Similiar days to your upcoming run/hike. I have played around with just about every combination of foods known to man. On my last multi day hike I tried an approach that would maximize fat burning without losing any energy. My food carry..... Maximize carbs. I ended up loosing about 6 lbs over the five days, which was the intent.

If i were doing a Similiar hike, say the GC R2R2R again I would take 250-300 carbs per hour of maltodextrin and use my fat stores for the rest. Possibly throw in a bit of protein, not much and your good to go. Doing multiday? Add a healthy dose of carbs to replenish glycogen at days end, and a good dose of protein for muscle regen and life is good.

I personally like making my own own Malto mix vs a product like Hammer Perpetuem. I can do it a lot cheaper and add a lot more flavors. I have finished off over 100lbs in the last couple of years and need to order another 50lb bag ( Thanks for the remiminder!). The last thing I want to do is get sick of a flavor and have to force feed myself. Even after 100lbs, I still find my magical Malto mix yummy.

One final point, I often will alternate hours..... One Malto one food. The food can be any high carb food such as my current favorites, Mounds or Reese's Cups.

Stephen Barber
(grampa) - MLife

Locale: SoCal
Fat burning on 12/31/2012 09:35:07 MST Print View

It takes about two weeks of low carb eating to transition the body into preferring ketones (fat) to carbs for fuel - so you won't be able to do it in 12 hrs!

Here's a link to a well researched book about the whole thing:

Chris W
(simplespirit) - MLife

Locale: .
Re: Turning fat into fuel on 12/31/2012 09:50:56 MST Print View

I'm far from the norm, but a friend and I did a 32ish mile hike in about 12 hours and I think I ate one or two 2-300 calorie snacks the entire time even though I have little if any body fat to spare. We did post-load at Waffle House, but I appear to have gotten through the day primarily on adrenaline. That's the best reason I can come up with anyway.

My wife and I eat primarily paleo (limited carbs and only from certain sources, unless we're not at home) these days so my body will pretty well burn whatever it has access to. I can feed it carbs or fat or a combination and have no issues maintaining a similar pace regardless. I honestly wish I had the funding to do some self-experimentation to figure out how/why it can do the things I put it through.

Edited by simplespirit on 12/31/2012 09:51:49 MST.

Hiking Malto
(gg-man) - F
Re: Re: Turning fat into fuel on 12/31/2012 10:57:14 MST Print View

"I'm far from the norm, but a friend and I did a 32ish mile hike in about 12 hours and I think I ate one or two 2-300 calorie snacks the entire time even though I have little if any body fat to spare. We did post-load at Waffle House, but I appear to have gotten through the day primarily on adrenaline. That's the best reason I can come up with anyway."

Actually I doubt you are far from the norm at all. Let's look at this 32 mile hike. I suspect you ate breakfast prior to leaving, let's say that is 500calories. Add to that another 600 snack calories. As Greg mentioned earlier the body has roughly 1500 calories in reserve as glycogen. That is a total of 2600 calories in addition to fat reserves. I know that you have mentioned that you have no fat reserves but this clearly is not case for a single day hike. So the remainder need to be drawn primarily from these fat reserves. Also if I remember correctly you are very light, 135? Lbs. let's use those numbers.

If you were doing what I call a normal 32 mile AT hike with maybe a mile of elevation gain I would estimate that you are burning roughly 135 calories per mile at your weight. For the full trip you would burn 4320 calories. So each hour you would burn roughly 384 calories. The question is when would you hit the wall? That all depends on your bodys ability to burn fat which is based on oval fitness level and specific training. But in your case you would have to burn 4320-2600=1720 calories over twelve hours if you pushed yourself to the brink of hitting the wall at the end of your hike. So could you burn 1720 calories over 12 hours. I would say no problem at all. That is only 143 calories per hour or a half a lb per day. I know for a fact that I can comfortably burn a lb of fat per day with no issue.

The interesting question would be how far could you push this? 35 miles, 40, 45? And what if you maintained a faster speed and did that hike in ten hours. I suspect you would start seeing what your limits are. I have tested eating 300 calories per hour and maintaining 3mph for up to 19 hours with over 15k in elevation gain. There was no indication that I was ever close to bonking on those hikes. I also know that I can run 20 miles eating nothing and not hit the wall. What I haven't done is purposely restrict caloric intake down to say 100 per hour to get a good feel for my actual fat burn rate. I may have to do this in the spring on one of my hikes.

Chris W
(simplespirit) - MLife

Locale: .
Re: Re: Re: Turning fat into fuel on 12/31/2012 12:17:45 MST Print View

Real numbers if you want them.

135 lbs @ 6% fat
300 cals for breakfast so say 1000 cals for the trip until post-hike gorging ensued
32 miles with ~ 2 miles gain and ~1.5 miles lost

Seems like we've done similar feats with similar results (I've done 18 miles with no breakfast, but I did eat one cliff bar during the run). After the 32 miler though, I'm not sure how much further I want to push it. Maybe I'm getting old at 33. :-)

I do agree I could likely spare 1/2 lb over a single day trip. Not much to spare like that for anything of significant length (days) though.

Edited by simplespirit on 12/31/2012 12:22:34 MST.

Hiking Malto
(gg-man) - F
How close? on 12/31/2012 12:51:42 MST Print View

With that amount of elevation gain and only a thousand calories I wonder how close you were to bonking? That's the sad part about trying to learn...... Now you have to do those 32 miles over again to then push to failure! :) And at 33 you're a young pup. I still feel like a young pup but at 47 but I'm sounding like my dad.

One final point. I know hat the OP is talking about a single day event. For multi day events you either need to finish the day with a "full tank" or start the next day half full and closer to breaking point. In Chris's case I doubt that a repeat of that hike the next day with similar calorie intake would have worked out as well unless his pig out at Waffle House did the trick. Also for very long duration hikes, there is only so much fat reserves to go around. Some, like Chris would hit that point quickly, others could likely go months.

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Turning fat into fuel on 12/31/2012 17:36:29 MST Print View

"I'm looking at doing a 40 mile run/hike (in 12 hrs) this upcoming summer and I'm not liking the fact that my pack will be full of so much food (fuel).

Anyone have any insight?"

For a run of the duration you are considering, I would highly recommend you read the article in the link below before deciding on what food to use. It's focus is on ibuprofen, but the underlying topic is the effects of eating complex food that ties up the digestive tract while engaged in endurance activities. It boils down to a competition between the working muscles and the digestive tract for blood supply, and the digestive tract loses, with troubling results.

Based on this article and my own experience with distance running and backpacking, I would advise you to limit your nutrient intake to simpler carbs that require almost no digestion before clearing the digestive tract. In combination with body fat, which also requires no digestion, you should be able to supply your body with ample energy substrate with something like 1500 calories of something like Perpetuem or one of the numerous gels on the market, i.e. 15-20 oz of nutrient, plus some electrolytes. I use Morton's Lite salt, but there are many other ways of going about it. The amount of nutrient will depend on your weight, but this will put you in the ball park. Hopefully Greg gressel will post to give you even more detail.

Edited: Oops, Greg had already laid it out. In any case, the article is worth a read, for the potential side effects of not doing it his way, especially if you are considering using ibuprofen.

Edited by ouzel on 12/31/2012 17:40:14 MST.

Gregory Petliski
(gregpphoto) - F
re on 01/01/2013 10:51:59 MST Print View

I wonder what people like the Tarahumara think of all this.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Tarahumara Food on 01/01/2013 11:06:47 MST Print View

They eat and drink like the rest of us.
But they've had lots of practice at it.

The "food" of choice is pinole. [Google is your friend]