Nutritionists commonly advise runners to eat a diet high in carbohydrates.  For example, the website Cool Running advises runners to consume 60% of calories from carbohydrates:

Carbohydrates are stored in the muscles as glycogen, the primary fuel you need to keep you moving. When this efficient source of energy wears out, so do you. You hit the wall and can go no further (often after about 90 minutes or two hours of running).

— Cool Running

“Hitting the wall” is a common challenge in marathons.  I remember how my legs would turn to wood after 15-16 miles and my mood would darken as well, as both muscles and brain were struggling with a diminished supply of energy.

Dealing with the wall in a marathon is no big deal, you simply grab a power bar, banana, gel, or some other sugary snack, and typically that’s enough to make it to the finish.  In an ultra-marathon, conventional wisdom is to consume 200-300 calories per hour from high-carb energy sources.  And there are runners who can do so for hours on end, such as Magdalena Lewy-Boulet, who won the 2015 Western States 100-mile race in 19:05 consuming nothing but GU energy products.

But not everyone can tolerate such a heavy load of carbohydrates, especially from products that are high in sugar and processed additives like a typical gel.  One study found gastro-intestinal issues reported by more than 80% of marathon runners during training and races.  And even the fastest competitors struggle, too.  For example, Anton Krupicka, an elite and highly respected trail racer, complained of feeling weak and nauseous during the 2014 Ultra Trail du Mont Blanc 100-mile race:

At first, marching up the hill to the Bertone Refuge was a pleasure. I was all alone, enjoying the still, clear night and the spectacular view of town’s lights receding quickly below me. Gradually, though, my stomach began to rebel at the thought of a gel, and by the time I made it to the aid station, I was full-on nauseous. As such, I quickly filled my flask with Coke there and continued on my way. For a while, I could sip on the Coke, but things only got worse with my stomach, and even though the trail here is a gently rolling contour over to the Bonatti Refuge, I wasn’t running nearly as much as I would had I managed to get more sugar into my bloodstream

— Anton Krupicka

Anton’s report is a classic example of the ultramarathon “bonk.”  Nausea might be the body’s signal that it cannot process any more carbohydrates due to the diversion of blood away from the digestive tract during exercise or the exhaustion of enzymes necessary to process sugars.  The feeling of weakness might be the consequence of an insulin spike, which clears excess blood sugar and stores it as fat, the problem being that fat cannot be burned and stored at the same time.  Notwithstanding Cool Running’s advice, fat burning makes up a large component of energy when running at moderate speeds characteristic of ultramarathons.

There may not be one answer for everyone, but there is an alternative to the high-carb approach:  burn fat as the primary energy source.  Scientists studying ultra-marathoners have found significantly greater capability to burn fat than conventional wisdom thought possible.  For example, Zach Bitter, who holds the US 100-mile race record of 11:47, recently reported that at 65% of his VO2 max, which would be just a little slower than a 7:15 minute mile pace, 98% of his energy was coming from fat and only 2% from carbohydrates.  He was a participating in a study which is seeking to measure physiological differences between athletes on different diets.  Zach is an advocate of a high-fat diet for a number of reasons, including the fact that by relying on fat stores, you can get away with eating less during races:

I strongly believe that the less you have to fuel during a race, the better. Not to mention that fueling can be a hassle, and if it can be minimized, the hassle lessens. There are a lot of other factors that come into play as well. Heat, for example, can greatly effect how the body accepts (or on super hot days, rejects) the calories you give it. This is why you see so many more stomachs turn at hot weather races. Less eating means your body can use its precious blood stores for cooling and muscle function, rather than for digestion.

— Zach Bitter

Few of us will be able to keep up with Zach in a 50 or 100-mile race.  But there may be ways for ordinary athletes to increase the efficiency with which they burn fat, for example, by shifting to a higher fat diet or reducing calories during training.  I used to run marathons carrying four or five gels, but after gradually reducing food consumed during training runs, I recently set a PR at Boston without any calories at all.  I now feel fine running all day without food, and friends of mine report similar experiences.

However, while most people’s fat stores are large, they’re not unlimited.  For really long races, there comes a point when the body needs more fuel, and if you burn up too much of your reserves, you might find yourself slowing down rather significantly.  For ultramarathons of 50 miles or longer, I now use home-made pemmican as my main source of nutrition.  In a recent 54-mile race in the Catskills, I consumed 1/2 lb. of pemmican and 2 dark chocolate bars (90% cocoa, containing less than 10 grams of sugar per bar) and felt quite good throughout and afterwards. Two weeks later, I thru-ran the 75-mile Shawangunk Ridge Trail in 24 hours and 8 minutes, consuming 1/2 lb. of pemmican and three chocolate bars.

If you haven’t heard of it before, pemmican is a mixture of dried meat and fat that was developed by the Cree and other Native American tribes and popular in times past with traders, explorers, scouts, and soldiers as a high-energy ration.  Pemmican is high in fat, contains virtually no carbohydrates, and if prepared properly is shelf-stable for an extended period of time.

Home-made Pemmican Recipe

Step 1:  Take a package of ground meat and roll it into thin sheets using a rolling pin and some wax paper.  Make the sheets as thin as possible.  I’ve made pemmican out of ground beef, but lamp, pork, chicken, salmon — any animal meat ought to work.  Native Americans used lean cuts from buffalo, elk, and venison, and they dried sheets of meat over the campfire.

Step 2:  Dry out the sheets of ground beef in a food dehydrator or the oven, at a temperature of around 140-150 F for 3-4 hours.  The goal is to remove the moisture, not to cook or burn the meat.  If it is thoroughly dried out, the meat should be shelf stable, i.e., it should last for a long time without going bad.  If there’s still moisture left in the meat, there’s a risk of mold.

Step 3:  Grind the dried beef into a powder, using a food processor or crushing it into small fragments with a fork.

Step 4:  Render suet into tallow.  You should be able to use any animal fat, and you may be able to find tallow or lard at the local butcher’s (in which case skip ahead to Step 5).  Suet is a large chunk of fat typically taken from the loins or around the kidneys.  Rendering it consists of melting the fat and separating it from other tissues.  To melt it faster, start by cutting the suet into small pieces, then heat it in a pot on the stove until you have a clear liquid.

Step 5:  Mix dried beef and hot tallow in a proportion of roughly 2:1.  Experiment with the proportion of fat and meat that suits your tastes.  It’s the fat that gives you the energy to keep moving, but few of us are used to eating pure fat.

Step 6:  As the tallow cools, it will turn cloudy, and you’ll be left with will be a mix that is reminiscent of extra-fatty hamburger.  This is pemmican.

In cold weather, you can carry little chunks of pemmican or form it into bars.  In warm weather, the fat will soften, and the pemmican will be crumbly and greasy.  You can eat it with a bowl and spoon, or just reach your fingers into a plastic bag.  If you have a campfire, you can cook it up with onions and potatoes.

While I prefer to keep carbohydrates to an extremely low amount during runs, there’s no rule that says you can’t mix some carbs into your pemmican.  Native Americans mixed in cranberries when presenting pemmican as a wedding gift.  Some people make pemmican with peanut butter or add in honey.  You can also jazz it up with spices.

There are new brands of energy bars based on meat, but they have too much sugar for me (close to a 1:1 ratio of fat and carbohydrates by weight) and I don’t care for the spices.  But they might be just right for you or someone else.

I’d love to hear from your regarding pemmican or other unconventional nutrition sources!  (Please leave a comment below)