There is a ton of good information in this thread and I’ve learned a lot.

I would like to offer a word of caution in that there could be other causes for the exhaustion such as a pathogen, blood anomaly, or other nutritional deficiency unrelated to caloric deficit; at least you now have a base line to work off of. You will have numerous opportunities in the future to reproduce those conditions and play with the variables. It wouldn’t hurt to have your blood values checked if this reoccurs and consulting a physician is never a bad idea.

Please update this thread when you think you’ve solved the puzzle.

On a truly long distance hike it takes a few weeks before the reality hits you. Then the hunger hits you hard. You basically can follow your hunger. You do not need to micro-manage your calories.

If your trip is long enough and you didn't estimate your food needs correctly, you can throw away unwanted food (or leave in hiker boxes) or purchase additional food. You spend a lot of time gravely eating as much as you can on your resupply days, too. In that way, there is no need to worry too much how precise you are because your body can withstand a period of insufficient food just fine but as soon as food is available, it will tell you what to do.

Your hunger will help you find food. You get really good at begging, mooching, looking really hungry with big puppy dog eyes at just the right moment, intuitively knowing how to find the restaurants in town with the biggest portions, how to find restaurants close enough to the trail for a short detour, etc.

I'm assuming your long distance hike would be on one of the national scenic trails and not in some totally remote or arctic place with no access to other people.

"my interest is also purely a weight saving issue, see if I can reduce pack weight by 1-2 lbs. with a higher fat content diet."

Since you are not doing thru hikes, why not make use of body fat and use a high carb diet to support its metabolism? It will enable you to reduce your carried food weight by however many body fat calories you can spare and the duration of your trips.

"I seem to have read somewhere that its possible to train the body to burn fat intakes better while at high intensity. not sure the specifics, have to try and find it."

It is a function of your VO2 max. The more oxygen you can deliver to your muscle cells the more efficiently you can burn fat at any given level of exertion. My hypothesis is that this also applies to efficiently utilizing fat at higher elevation; the greater percentage of what oxygen there is at higher elevations that you can extract and deliver to your muscle cells, the more efficiently you will metabolize any substrate at a given level of exertion.

This link gives a pretty straightforward explanation of the variables and processes involved, IMO.


http://www.uta.edu/faculty/blevinsj/August%2026/metab2%20notes.pdf

"Careful here. There is an upper bound on how many calories you can metabolize from fat per day without catabolizing muscle protein.

I think it's 31 calories per lb of fat.... I may be wrong though and will have to look it up but that seems about right."

Could you supply references for this, Kevin? This is the first I have ever heard of such a limit, and I would like to know more.

"I'm no where NEAR my daily calorie requirements..."

You have to be supplying the energy from somewhere to perform the work necessary to complete the requisite number of miles. The answer is almost certainly body fat, at least on trips less than, say, 2 weeks, depending on your body composition.

Diane,

"You basically can follow your hunger."

That's a very helpful thought, seeing as you've done the PCT and I haven't. In the 1 to 2 week range, I definitely can lose weight and to a point where I couldn't sustain it for an entire summer. But obviously there are cultures and professions that involve season-long high exertion and people's bodies adjust (assuming there is food available).

"I'm assuming you are . . . not in some totally remote or arctic place with no access to other people."

What I find in a wilderness setting, including the Arctic, is that I shift slightly from hiker to hunter-gatherer (walk slower, graze more). Those berries, clams, fish, etc, start looking pretty tasty if I've under packed on the store-bought food. You're not allowed to eat the black bears on the JMT, but in my area, you are. I did that last May and also gathered fiddleheads (fern buds) for pesto on the pasta. But that weren't needed calories, it was just showing off as camp cook.

"You're not allowed to eat the black bears on the JMT, but in my area, you are."

More significantly, in Alaska the brown bears may be attempting to boost their calorie intake with you in mind.

--B.G.--

> On a truly long distance hike it takes a few weeks before the reality hits you. Then
> the hunger hits you hard. You basically can follow your hunger. You do not need to
> micro-manage your calories.
Yup.

I do remember one rather long, late autumn trip where we had budgeted our normal rations and put in a number of food drops on that basis. But we sort of 'got going' towards the end and started clocking up 1.5 day stages. But we were eating 1.5 day rations!

Cheers

"Careful here. There is an upper bound on how many calories you can metabolize from fat per day without catabolizing muscle protein. I think it's 31 calories per lb of fat.... I may be wrong though and will have to look it up but that seems about right."

This seems very, very low, even if one assumes minimal protein intake, and it's not immediately obvious that the underlying rate-limiting metabolic processes would depend on total fat stores (thus the "per lb"). With reasonable protein and carbohydrate intake during the day, I would expect to get my 3500 calories from a pound of fat without catabolizing muscle protein. Evidence to the contrary? Have I missed something?

Bill S.

Edited by sbill9000 on 01/12/2013 05:39:03 MST.

Kevin -
"It's clear that many of us burn from 6000-10000 calories per day."
...
"At 250 calories per bar, and 8000 calories, ..."
...
"I'm no where NEAR my daily calorie requirements..."

This may sound a little harsh. That's not my intent. I just lack social skills ;-)

You are extrapolating from generalities, and then asking for the specifics on what should work for you. Others are working from personal, measured, tested experience.

How much weight do you lose on a two to four week hike? (measured before the post trip pig-out.)
How many calories did you carry? (from the spreadsheet)
What calories did you add along the way, or carry out?
What was the ratio of F/P/CH?

For ambitious, long term, long distance hikes, you can only figure out what happens For You if you compare calories-in versus weight lost. The guesstimates provided around the web can serve as a good starting point for Hike #1, but for Hike #2 you should be applying what you learned, adjusting, and then iterating again.

Until you provide some specifics this discussion will just keep going round and round.

And if you want to talk theory that's fine. But without references it starts to sound like opinion.

Happy Trails.

Edited by greg23 on 01/12/2013 15:55:02 MST.

This should be a good anchor point for calories required.
Andrew Skurka is a machine in terms of time, distance, and duration.
He didn't evaporate by the end of his 4,700 mile Alaska-Yukon trek.



I will opine ;-) that for to many, 31% fat is a lot, but offer that for a highly trained endurance athlete this is not uncommon.

Edited by greg23 on 01/12/2013 11:03:29 MST.

Caloric needs depend partially on how much energy is expended but also upon how efficiently the individual is in converting food to energy.

Back on the farm we used a term called "easy keeper." Some cattle fattened more easily on the same food.

On long hikes it's been my experience that many hikers will plateau in weight loss, often losing weight rapidly at first and then losing more slowly or even gaining slightly after several months. On my first thru-hike I was hungry most of the time. On more recent hikes it's barely an issue. People are amazingly adaptable when necessary.

I believe there are three easy reasons that hikers weight plague during their hike.
1) they drop body and pack weight and hence burn less calories.
2) hikers eat more later in the hike so more calories in.
3) I believe most hiker become much more efficient. Feet don't lift as high, arms don't swing as much. I have heard it called the thru hiker walk. I saw this clearly on the AT when I moved from GA to PA. The mechanics of the walk is much more efficient.

"I will opine ;-) that for to many, 31% fat is a lot, but offer that for a highly trained endurance athlete this is not uncommon."

For me, the more meaningful numbers would be expressed in terms of daily calories, as follows: Fat = 51%; carbs = 39%; protein = 10%; and this only includes dietary calories. As lean as Skurka is, there will almost certainly be a certain amount of calories obtained from body fat. As things stand, his calories derived from carbs is down in the high 30's as a percentage of just dietary calories. If body fat is factored in, his numbers will start to approximate those supplied by Richard Nisley in the following post to a query of mine several years ago. He also has some pretty informative charts of substrate use correlated with intensity of exercise that he would probably be willing to share upon request.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=4608

Ignoring the specific calories (because I haven't counted in years, and usually plan food for a family), I've found that the amount of food I need to function ratchets up over the course of a long hike.

0-2 weeks, I eat about as much as I would on an overnighter.

2 weeks - 2 months, I keep ratcheting up the food, until I've almost doubled the weight I'm eating per day.

After 2 months, I find it stays pretty similar, though I do pig out in towns.

If it's a lower energy-requiring trip (say, going at the speed of my kids), this doesn't apply as strongly.

"2) hikers eat more later in the hike so more calories in."

+1 This is precisely the approach used by Dial, Gek, and Jordan on the Arctic 1000 as they progressively exhausted their body fat and had to depend more and more on dietary calories. They were taking in somewhere in the vicinity of 7000 calories/day toward the end, IIRC.

"3) I believe most hiker become much more efficient. Feet don't lift as high, arms don't swing as much. I have heard it called the thru hiker walk. I saw this clearly on the AT when I moved from GA to PA. The mechanics of the walk is much more efficient."

+1 Analagous to the ultramarathoner's "shuffle". Looks weird to shorter distance runners, but very efficient over the longer distances.

Regarding the "easy keeper" and the thru-hiker walk/efficiency gains...So true!

You won't waste away to nothingness on a long distance hike. You first will lose all that excess weight you are carrying around down to some set-point, including any excess glycogen puff and excess abdominal blubber. Depending on your own set-point, you may lose all of it or retain some of it. I'm an "easy keeper" for sure, retaining plenty of womanly flesh, some quite unwanted.

Once you get down to that set-point, your hunger will make demands on you that you cannot ignore. You will eat more even if you have to hike faster so that your food rations can stretch over fewer days (and fewer hungry nights.) Your hunger will wait patiently and then pounce on the first chance it gets.

Meanwhile, you will become more efficient in your metabolism and your movements. I know lots of things inside me slowed or changed.

I remember many days walking into town and literally watching color return to my vision as I ate my first meal and then bursting into tears. Things shut down inside me to preserve energy, including some sort of unnamed life force of emotion and my senses.

I also remember watching my shadow bounce down the trail thinking to myself what a huge waste of energy. After a few hundred miles there was no more bounce in my gait.

Kevin
I'm new to backpacking so my experiences come from other events. I find I bonk when any of the 3 (fuel, liquids & electrolytes) get low. But it can be reversed quickly. I bonked from low sodium on a double century ride & 20 min after drinking a V8 (1200mg of salt) I was good again. I bonked twice in the same day on the death ride.
When I did the full Ironman I burned 10,284 calories (via heart-rate monitor), yet only consumed half of that throughout the day.
A good source of info on this is from http://www.hammernutrition.com
I hopes it helps.
thx
Brian

A couple of other issues here. Body fat is not directly usable as energy - it needs to be processed in the liver into ATP, but this is a slow process, and can be a potential chokepoint. On a sustained basis, you are probably looking at around 0.3-0.5 grams of fat oxidation an hour, or 160-270 calories per hour from fat.

The body has reserves of about 2000 calories of usable energy.

Protein and fat are slow to digest (5-7 hours), whereas simple carbs digest in 20 minutes, and complex carbs in a couple of hours.

So with a fat heavy diet, it is still possible to bonk by using up your usable reserves and energy from fat just not becoming available fast enough to replace it, even if you are technically getting enough calories overall. This is the science behind Greg's buddy's problem of not enough carbs during the day.

Personally, I tend to go heavier on fat for meals, and heavier on carbs for snacks through the day. Dinner makes an ideal time for fat consumption, as your body has enough time to process it, and also the body heat generated from slow digestion of fats will help keep you warm throughout the night.

Also, some people here are throwing round some very large calorie numbers. One thing to be aware of is that the standard convention for calorie counting includes your underlying metabolism in exercise figures. This is no big deal for a 30 minute 5K run. But for hiking 12 hours a day, this is substantial double count, and you are probably overestimating calories burned by about 1000.

Edited by mcalista on 01/18/2013 08:08:29 MST.

"Body fat is not directly usable as energy - it needs to be processed in the liver into ATP, but this is a slow process, and can be a potential chokepoint."

That is flat out wrong.

http://en.wikipedia.org/wiki/Fatty_acid_metabolism

"The body has reserves of about 2000 calories of usable energy."

Wrong again. The body can store about 2000 calories of glycogen, more or less. The total amount of usable energy is equal to that glycogen plus 3500 calories X total pounds of body fat plus a considerable amount of calories potential from catabolizing muscle protein. However, no one should ever end up using ALL their body fat, or very much muscle protein, without risking serious health consequences.