Metabolism on the Pacific Crest Trail

According to the book Where the Waters Divide: A Walk along America’s Continental Divide:

On a long-distance hike, food is fuel, and human bodies are gas-guzzling automobiles. Carrying a pack at high altitude and walking at a fair pace over difficult terrain, a hiker uses up about 300 calories a mile. To walk 15 or so miles per day requires at least 4,500 calories just to keep going.

I suspect that 300 calorie/mile figure is based on male hikers, and that averages for female hikers are lower. Men tend to have significantly higher metabolism rates than women, though this is based on averages – there are individual women who have relatively high metabolism rates, and men who have relatively low metabolism rates.

Based on all of the accounts of long-distance hikes on the Pacific Crest Trail that I’ve heard and read, men hikers do seem to lose weight faster and be more vulnerable to malnutrition than female hikers. I haven’t scientifically proven that this is because male hikers tend to have high metabolism rates, but it’s the most plausible explanation that I can think of.

Reduced vulnerability to malnutrition (and being able to get away with carrying less food) are benefits to hiking with a lower metabolism. However, a higher metabolism rate reduces vulnerability to hypothermia, especially during sleep. Men tend to be ‘warm sleepers’ (i.e. they can get away with less warm bedding), and women tend to be ‘cold sleepers’ (i.e. they need warmer bedding), though, once again, not all women and men are average.

Though I don’t know for sure, I suspect I have higher than average metabolism for a woman, but lower than average for a man. I eat more food than a lot of people (I’m used to people commenting ‘wow how are you going to eat all of that food’) and I think I sleep warmer than a lot of women.

However, if a hiker needs only 200 calories per mile, and they hike 15 miles, that’s still 3000 calories in a day just for hiking. The highest mileage I did in a single day was 23 miles, and some hikers, especially thruhikers, do more than that on a regular basis. My average pace when I was hiking through Washington – including my zero days (when I did not hike on the trail) – was 14.2 miles per day. A lot of hikers, especially thruhikers have a higher average mileage/day.

In my big hike in the summer of 2017, I generally only carried enough food to eat at a rate of 2500 calories per day, and since I usually arrived at my next resupply point with leftover food, that meant most days on trail I was eating less than 2500 calories/day in food. Therefore, even though I don’t know what my exact metabolism rate was, I am certain that I had sustained calorie deficits.

I did not measure my weight before, during, or after my hiking, but the weight loss was obvious enough that I could tell it happened without measuring myself and I think returned to my pre-hike weight about a couple months after the end of the trip.

There are various reasons why I prefer section hiking over thruhiking, and (not) having to deal with months of calorie deficits is one of them. Even though I would be unlikely to reach an dangerous level of malnutrition, I would rather not go there.

Of course, when I was in town, I ate a lot. Towns meant lots of food which I did not have to carry with me. I especially remember really eating it up in White Pass (it helped that the Kracker Barrel Store had surprisingly good food). In Snoqualmie Pass, I remember pushing myself to eat much more than I felt like eating because I knew, intellectually, that I had regular calorie deficits, and I wanted to compensate for that (though I will say that Commonwealth, a restaurant in Snoqualmie Pass, offered me the best meal I ate during my entire Washington PCT hike). By the time I was in Stehekin, I was less concerned about cramming the calories because I was so close to Canada, so I just ate in accordance with my appetite.

I am happy to say I never experienced ‘hiker hunger’ during my 36-day-long hike. I also was not particularly hungry when I was in Manning Park, or when I was on Denman Island.

Then I went to Vancouver (the city, not the island).

When I was in Vancouver, I was eating 4-5 full meals per day. I did not feel desperately hungry, but one meal was not quite enough to make me feel full, so I ate another one two hours later. And I was gorging on restaurant food since it had been over a month since I had regular access to a variety of restaurants (as opposed to 1-2 restaurants in a small town). I have never spent so much money on food per day as when I was in Vancouver.

Did I eat so much food in Vancouver because I was on the edge of hiker hunger? If so, why did it manifest a week after I had stopped hiking, and not in Manning Park or on Denman Island?

Then, during the first month after my return to San Francisco, something strange happened.

If I delayed/missed a meal at all past my habitual time, I would feel painfully hungry. It was hunger unlike anything I experienced during my trip.

My best guess is that I ended my hike just around the time I exhausted my fat reserves. In Manning Park / Denman Island I was probably eating about as many calories as I was burning, so I was no longer in calorie deficit, but I was also not rebuilding my fat reserves. In Vancouver, I started to rebuild my fat reserves (and probably compensating for other nutritional deficiencies with the greater variety of food). But because my fat reserves remained low for the entire month after my hike, any disturbance in my eating schedule was enough to make my belly scream with hunger.

I’m not sure that my conjecture is correct. But I am just as motivated as ever to try to avoid getting hiker hunger while I am on trail.