Reader question: How would I fuel during a long run?

A couple of weeks ago, SteveL asked me in the comments:

“How would you fuel during a long run?”

Allow me to be a bit tongue-in-cheek here. If SteveL means what we usually do by “long run”—that is, a training run and not a race—my answer is, “with body fat and oxygen.” In other words, not at all.

The physiological details of this are best left to another post, but the short answer is this: the goal of a long run is not just to run for a long time, but to develop the system that helps us run long. Crucially, that system is known as the aerobic system, which you can think of as the system that burns fats in presence of oxygen.

Here’s the critical detail: the fat you eat doesn’t reach your bloodstream for a few hours. So, unless your long run is very long, any fats you ingest during the run aren’t really going to go towards fueling that run.

Let’s discuss the more conventional fuels people use on their long run (sugar-laden fuels such as a 3-6% carb solution or gels). Great for races, but I’ll get to that in a bit. If you ingest them during a training run, you’re enabling your body to lean on its sugar-burning energy system (which it uses for short-duration, high-intensity bouts) for a long time.  This means 3 things:

  1. First and foremost, it enables your long run to be faster than is healthy: you’re liable to do what looks like a long run but is actually a bunch of short, medium/high-intensity training runs that in aggregate masquerade as a long run.
  2. Because you’re fueled with sugar lets your aerobic (fat-burning) system off the hook , which is the system that is supposed to power your long run.
  3. You’re using the short-duration, high-intensity (sugar-burning) system for a what should theoretically be a long-duration, low-intensity activity (which you’re effectively turning into a long-duration, medium/high intensity activity). You’ll wear your body down disproportionately.

To recap: no fuel for long training runs. Fats won’t help, and sugar is counterproductive.

(While the body does burn a mix of sugar and fat at all times, the longer the duration, the more fat should be in the mixture. Because the rate of fat-burning peaks at around 50-55% maximum work rate for most people, very long training sessions shouldn’t exceed this low intensity.)

Fueling during a race

Fueling during a race is different. You’re not trying to train anything here. You’re trying to get every bit of power you can from the machinery you’ve been developing in training, with the provisos that you (1) finish the race and (2) don’t blow the engine.

This means that you want to make sure you’re well-fueled (and you stay well-fueled) during a race. For anything that’s marathon length or below, fats still won’t help. For the vast majority of us, it’s still too short of a race. So, such races are the ones you want to approach with the run-of-the-mill advice on race fueling: your carb solutions and gels work great here.

There’s one consideration: don’t start fueling until you’re 20-30 minutes into the race. When your body isn’t already warmed up, it’s very easy for a shot of sugar to kick up your insulin levels, which reduces your fat-burning ability. But once you’re warmed up and burning fats at a high level, sugar has a much smaller effect.

 Fueling during an ultramarathon

Here’s where it gets tricky. There’s two sets of priorities to discuss: the physiological needs of the body and the practicality of fueling on the run.

The physiological needs:

  • Hydration (water plus electrolytes)
  • Nutrition (the right combination of macronutrients)
  • Digestion (continued function of digestive system throughout the run).

The practicality of fueling on the run:

  • Combining hydration with nutrition.
  • Creating a food that fits easily through the valve of a handheld water bottle.

Here’s a drink recipe which (for me) meets all these criteria:

Basic Ultramarathon fuel 



  1. Add 1 cup of water into blender.
  2. Add all ingredients (heavier ingredients first).
  3. Blend on low until well-chopped.
  4. Add the rest of the water.
  5. Blend until smooth.
This is what I use…

Nutrition Facts_1

Nutritional Rationale


For a recipe such as this, I usually drink one serving (about 42 oz) over a period of 2-3 hours. This generally takes care of both my fueling and hydration concerns.

This suggestion is a TEMPLATE for people to try out during training runs. It’s important to adapt this or any recipe, workout, training plan, or racing strategy to your personal needs.


The reason I like including sizeable portions of all 3 macronutrients (carbs, fats, and proteins), is to incentivize the body to maintain the digestive system activated in a low-key but comprehensive way. This applies for protein in particular: while protein will not go towards fueling the body during a race, I put a small amount of it in order to create a more balanced digestion process.

The same goes with fiber (occurring mostly in the spinach, blueberries, and chia seeds). Ultramarathoners are prone to cramps, indigestion, and other digestive issues during the race. By putting a small amount of natural fiber in here (not so much that it slows down digestion), we can help “smooth out” digestion during the race.


As you’ll notice, one serving of this drink has a staggering amount of potassium (almost 1.3g) and a respectable amount of sodium (just over 0.13g). The reason I like this 10:1 ratio of potassium to sodium is because a lack of potassium is linked to muscle cramps, and reduced nervous system function. (This can lead to lower coordination and reaction time, which can cause an injury).

Generally speaking, more potassium is better (up to a point, of course). 130 mg of sodium every 2-3 of hours is quite enough to keep a well-adapted athlete going during a long race.

Carbs and fat

The sugar calories are straightforward: these will go towards topping off your glycogen tank, in order to stave off fatigue and help your aerobic engine continue to burn fats.

Now we get to the tricky bit. Supposing that you drink 1 serving of the recipe in 2 hours, you’re getting around 160 calories of carbs and 155 calories of fats an hour. You might think that’s not really a lot of carbs. However, that’s the reason a majority of the fats in the drink come from medium chain triglycerides (MCTs), sourced from coconut oil.

Why MCTs?

MCTs are relatively easy to digest relative to other fats, and they also become available for fat-burning very quickly upon hitting the bloodstream, helping to increase fat-burning and accelerating the metabolism. In other words, “reducing” the possible sugar content of this drink by balancing it out with coconut oil is an excellent strategy for endurance races.



Athletic training: a game of physiological Jenga.

The 80-20 rule in athletic training* goes like this: train 80% of the time at a low intensity and 20% of the time at a high intensity, and you’ll achieve the best results.

Understandably, a lot of people—particularly us urbanites who are extremely busy and almost completely devoid of free time—might say: “but I only have a few hours to spare every week! I can’t afford to run slowly 80% of the time. How can I possibly expect to make gains?”

(Or something like that.)

This is exactly the wrong question. What running (a.k.a. training) at a low relative intensity—which people often refer to as “running slowly” does for the body is that it develops the aerobic system. (For most, but not all of us, training at a low relative intensity does indeed mean running slowly.) The aerobic system is extremely important: it mitigates oxidative stress (also known as chemical aging), it helps us recover from anaerobic efforts by processing lactate, and it keeps us well-fueled over the long-term by burning fats.

The aerobic system is the very foundation upon which any “gains” are built. In this sense, aerobic training increases what I like to call our “physiological capital,” that we can invest in high-intensity (anaerobic) training and develop what we typically refer to as “strength” and “power.”

To explain this relationship, I like to use the metaphor of a Jenga Tower.

Suppose that you have a particular strength or power goal: you want to run 6 minute miles. This is equivalent to wanting your Jenga tower to be 10 levels tall. But the problem is that you only have 20 bricks (each full level of a Jenga tower is 3 bricks).

The result is that you can only build 6 complete levels to your Jenga tower. You’re faced with a stark choice: you need to add levels to get to 10. But you don’t have any more bricks. So you’re forced to take from the lower levels. (This is essentially what strength training does). Your tower gets higher and higher—which is fine, until you pull out or lay a brick juust too quickly or a light breeze comes along—and the tower, which had grown increasingly unstable, plummets to the ground.

(You’ve just become injured.)

But there’s a way to add bricks to the base of your tower: aerobic training. This is what I mean by “increasing our physiological capital.” While aerobic training adds bricks at a pretty good rate, left to its own devices it turns your tower into a pyramid: the lowest level grows wider, until at some point  your body decides to start growing the next level.

That’s not a bad thing: a lot of ultrarunners (the healthy ones) have metabolisms that look like a shield volcano: gargantuan aerobic systems, but very little power. (If the height of the tower is how much power you possess, then the width of the base is how much distance you’re good for.)


That said, it’s not necessary to build a pyramid, when it’s a tower you want. Although it’s important that your tower be stable, that’s about it: most of us are not trying to be an ultrarunner, nor do we have to be. All you really need is a few extra bricks around your base—enough to plug any holes you may have created, and to be able to add a couple of levels. Rinse and repeat.

A quick disclaimer: the body doesn’t convert the actual aerobic machinery into anaerobic machinery in the way that a naïve reading of the “Jenga metaphor” would suggest: the brick that you take from the base is not literally the same one you put on top of the tower. However, the reason I like the Jenga metaphor is because the stress and wear-and-tear incurred by anaerobic work (compounded by the fact that it is the job of the aerobic system to absorb those stresses), means that the process of adding strength and power basically always means carving into your aerobic base.

How often do you switch from adding bricks to adding levels? If you’re looking to run an endurance race, for example, then you need a very wide aerobic base.

Supposing that you want to develop some all-around fitness, a basic (but certainly not universally applicable) recipe is this:

  1. For 2 weeks, train primarily easy 95-100% of your training.
  2. The next 2 weeks, train at a moderate-to-high intensity 35-40% of the time.
  3. Rinse and repeat.

This process will give your body two weeks to recover well from strength training (read: replenish the bricks you took from the base, and add a few more). Two weeks of low-intensity training isn’t really long enough to start losing high-end fitness: the small amount of strength training 0-5% during the easy weeks is more than enough to maintain your gains. But when you’ve cycled through this process several times is when you’ll really start to see your gains stack up.

Building and maintaining an aerobic base, and making sure that our strength gains are well-buttressed by wide lower levels of our metabolic tower, is non-negotiable. Some of us are lucky: for good or ill we spent our formative years playing at the beach, kicking around a soccer ball, or going hiking with our oudoorsy parents. This person (unbeknownst to them) has been stacking more and more bricks around the base their fledgling tower, broadening their aerobic base until they’ve accrued what seems like a limitless amount of bricks.

Others never had that chance.

But not having had that chance doesn’t mean we have any more of a choice. Sometimes, the unconscionable choice—running “slowly” despite the horrible feeling that time is slipping away and we’re not getting any faster (forgetting the fact that our pool of bricks is growing ever larger)—is also the right one. That choice will put us in a position from which we can develop speed . . . and get to keep it.

*NOT the Pareto Principle.