An Experiment with (Lack of) Nutrition

Yesterday I conducted a little experiment to see just how few calories and electrolytes I could consume during an endurance event.  It involved hiking from the rim of the Grand Canyon down to the Colorado River and back--which is 15+ miles roundtrip, with 4500 feet elevation loss and gain.  Here's how it transpired.

I Really Wasn't Intending to Go That Far...
I had spent a few hiking and riding along the rim of the Canyon, including a 50-mile ride along the rim the day before.  This was to be my first venture below the rim, and I was only planning on going halfway down--which would have been an easy 3-hour round-trip hike.  So I threw a few Clif bars and a handful of gels into my pack, filled a few water bottles, and headed down the Bright Angel trail.

As much as I had been enthralled by the view from the rim--I was completely unprepared for how spectacular the canyon looks from below.  I was captivated, and reached the halfway point in no time--and wanted more.  The river was calling me but was still over 2000 feet below.  I wasn't concerned with my stamina in getting back up--but knew I had a lot less food than I'd have preferred to make such a journey. 

Taking Stock of My Rations
Water isn't a concern on this trail during the summer--it's available at 1300', 2300', and 3300' below the rim.  But calories? Only what you bring with you.  Here's what I had in my pack:

• 3 Clif bars (250 calories each)
• 5 gel packets (100 calories each)
• A few unsalted almonds (maybe 100 calories)
• Grand Total:  1350 calories, with very few electrolytes or sodium

I guessed that the round-trip would take me 8 hours.  On something like an 8-hour bike ride, I would consume 300 calories an hour,with at least 100/hour of that from a sports drink to replenish electrolytes.  That would be 2400 calories.  Did I really have enough to make this trip without bonking?

How Much Did I Really Need?
During aerobic endurance events, our bodies get energy from two sources--body fat, and glucose.  We get glucose from muscle glycogen and blood glucose  (which comes from ingesting carbohydrates).  In general, the slower we are going the greater the percentage that comes from stored body fat.  For a hike like this, maybe 60% of my energy would be coming from body fat if I took things at a leisurely pace. For contrast, race pace during a sprint- or olympic-distance triathlon would use maybe 80% glucose and 20% fat.

At 157 pounds and 7% body fat, I'm carrying about 3-5 pounds of nonessential body fat.  At 3500 calories per pound, that's 10,000 to 15,000 calories worth (the equivalent of 100-150 gel packets!).  Obviously, enough for a day of hiking.

Our muscles can store around 2000 calories--but only if we've replenished them with good carbs after a long workout.  After my 50-mile ride the day before, I had eaten a burger and fries, plus a few cookies.  So I was pretty low in the muscle-glycogen department...

For this type of hiking, I'm thinking I was burning 400-450 calories per hour.  For my projected 8 hour finish time, I would need 3200-3600 calories.  Assuming 50% to 60% would come from stored body fat (1600 to 2100 calories), I would need 1100-2000 from glucose.  Assuming I should be able to get at least 1000 calories from muscle glycogen, I shouldn't need more than 900 from ingested glucose.  My 1350 should have been plenty.

All Calculations Aside...
Sitting along the trail halfway down the canyon, I didn't actually do the above calculations.  Rather, I did the rough guess, "Oh, it'll probably be enough.  If it's not, I'll beg from other hikers..."  Yes, I know this is the kind of thinking that the Search & Rescue workers hate...

Actually, I was concerned about my lack of electrolytes and sodium, and the possibility of hyponatremia.  But the day was not that hot--maybe 65 degrees at the rim and the low 90s at the bottom.  Plus, there was a partial cloud cover.  Which all meant that if I went slow, I wouldn't sweat much, wouldn't get too hot, and wouldn't need to drink too much water.  If it had been hot and sunny, I definitely would NOT have proceeded without electrolytes!

Here's How it Went
I planned to eat a little on the way down, some more at the river, and the rest halfway back up.  And consciously limit my water intake, while monitoring urine output and color (frequent and clear urine can be a sign of hyponatremia; infrequent and dark yellow urine means you're dehydrated).  The river was gorgeous, and the view from the inner canyon was surreal. (It really is indescribable, so I won't try.  Just trust me when I say "go do it'.)

After a half-hour on the bottom, I headed back up.  All was going well, except I was urinating a bit more (and a bit clearer) than I'd have preferred.  It was really, really hard to not drink water, as it was hot and dry on bottom.  I kept wanting to wet my mouth.

And about a third of the way up I started to feel a little light headed, and a little dizzy.  I knew immediately that this was the start of a bonk.  So I stopped and ate the rest of my food--a Clif bar and two gels.  After resting 10 minutes, I started walking again and felt great.

In fact, I felt so great that I continued up at an easy steady pace without further breaks, except for a 10-minute stop when the clouds broke to let the sun drop below the rim. And it felt really good to pass all of the 20-somethings who had nearly sprinted off the river bottom but who were now wilting near the top... Also near the top, a Park Ranger was assisting a young man who looked not-so-great.  I'm guessing it was either dehydration or lack of food.

The After Effects
At the top, I knew I needed carbs and salt.  Thankfully, on the South Rim, there are stores aplently.  A big soft pretzel hit the spot, as well as a small bag of Fritos.  Back at the car, I downed 20 ounces of Gatorade in about 30 seconds.  Electrolytes, indeed.  A shower was followed by a steak and potatoes meal (with plenty of salt).

I thought I was recovering fine, but woke up this morning with an incredible headache--it felt exactly like an alcohol hangover.  I spent the day as a zombie, and have drank probably 4 quarts of Gatorade.  As I write this, 24 hours after finishing the hike, my headache if finally starting to go away. 

So, yes, the lack of electrolytes & sodium caught up with me.

Conclusions Drawn

• The rule of thumb to consume 200-300 calories per hour during endurance activities is a good one.  During this slow-paced one I consumed 150 per hour, and almost bonked.
• Be sure to replenish muscle glycogen after a workout--had I eaten good carbs after my 50 mile ride the day before, I likely would have had enough muscle glycogen to have carried me through.
• Especially in hot conditions where you're drinking a lot of water over many hours, be sure to have a sodium/electrolyte replacement.

 

Comments

[gretchen]

So I'm assuming pizza is not "good carbs" either? :) So what would you recommend after a long workout?

[Brian Maiorano]

I'm sure nutritionists will roll their eyes at me, but I think certain types of pizza are just fine in moderation. You have to pick carefully, but you can find ones with a non-greasy crust that give a good balance of carbs/protein/fat. I stay away from the meat toppings because of the fat, sodium and preservatives--but otherwise I bet a week or two doesn't go by without me finding a good slice or two. In fact, at Saturday's triathlon the official post-race food was pizza--and I had pizza after a workout the weekend before, too.

After a long workout I tend to forget about the notion of "good carbs" (ie: veggies, whole grains, etc.). In fact, foods with a high glycemic index http://www.diabetesnet.com/diabetes_food_diet/glycemic_index.php are exactly what you need in the hour or two after a long workout. They (along with a bit of protein) will most quickly replenish the glycogen your muscles have lost.

I try to keep snack-type items around that fit that bill--pretzels, cereal, crackers with peanut butter, bagels, or a baked potato to throw in the microwave. Once I take that ohmygod-I'm-famished edge off with maybe 400-600 calories, I can think about having a healthy, balanced meal a couple of hours later.

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Brian Maiorano
www.SmarterTriathlete.com