THE KINETIC CEILING: WHY ULTRA-ENDURANCE NUTRITION MATTERS
By Nicholas Miller
Running is becoming popular. With a surplus in investment into races, a formerly niche sport has now hit the spotlight: ultra-running. Over the last decade, participation has grown by more than 300%, driven by increased interest in personal challenges, community support, and trail accessibility. Consequently, a positive feedback loop has formed, in which ultra-running events can leverage this surplus to promote and turn a grassroots race of 20 people into a full-blown “trail fest” with well over 200 participants. The result? People are skipping the now insignificant 5K and Half-Marathon to jump straight into ultra distances.
WHAT HAPPENS IF WE KEEP RUNNING?
An average person running a 50K (31mi) race needs around 4,000 calories; however, our endogenous glycogen stores are capped at about 2,000 calories. Your body literally “runs out of gas.”
To make up the other 2,000 calories, we rely on our “Gut”; but when we stress our muscles, in this case by running, our sympathetic nervous system reroutes around 80 percent of GI blood flow to working muscles. This process is called Splanchnic Shunt.
In this state, our gut must absorb fuel with a fraction of its normal blood supply, which causes those traditional GI issues. There is no powering through that.
THE WHY BEHIND THE WHAT (WE EAT)
By this point, our digestive system doesn’t care what “tastes good,” and trust me, almost nothing will, it cares about what has…
- A) The lowest Activation Energy (Ea)
The reasoning behind this is that with a lower activation energy, substances are easier to digest, and vice versa. “Runner’s stomach” is characterized by abdominal pain, cramping, nausea, vomiting, or diarrhea during or after exercise…common themes in indigestion. Many runners also talk about a “sloshing” feeling when they run without the right fuel, likely because a significant amount of undigested food lingers in their intestines.
This brings us to the first great innovation of scientists: the gel. With a running gel, you can drastically lower your activation energy with a hydrolyzed substance. Based on the iconic 𝑞=𝑚𝑐Δ𝑇, a lower concentration (of particles) equates to a higher heat energy. Gels reduce the mechanical work of digestion, requiring less energy to break down than a solid bolus. Another pro is that these gels are easier to eat if you do end up being nauseous.
Still, if you are craving something solid–which is quite nice after being out on the trail for a good amount of time–or are trying to track or measure your inputs in fractions of a package, there are also energy chews that work in a similar manner (rapid absorption, similar effect onsets, and activation energy) by being made up of simple sugars.
- B) The Lowest Osmotic Pressure (Π)
Osmotic pressure is the minimum pressure required to prevent the passive flow of a solvent across a semipermeable membrane into a more concentrated solution. In Layman’s terms, it’s a factor of whether or not your body needs to supply water from the bloodstream to digest something.
Specifically, looking at the van ‘t Hoff Law (Π=𝑖𝑀𝑅𝑇), simple sugars create high pressure that pulls water from the blood, once again causing bloating, cramping, and that iconic “sloshy” feeling.
The fix here is slightly different, but still something we see in gels and chews we run today: a massive branched polymer rather than a slew of individual molecules. With one long “chain,” these polymers sit at very low molar concentration (𝑀), resulting in near-zero osmotic pressure, thus no “water tax.” An additional benefit of a low molar concentration is that your GI tract will experience very rapid gastric emptying.
- C) The ability to absorb the largest amount of energy quickly
Giving our body “fuel” is only half the problem; getting it into the bloodstream is the other half. According to Michaelis-Menten kinetics, a model that describes how enzyme concentration, substrate concentration, and reaction rates relate to each other in terms of velocity.
Michaelis-Menten Equation: V0 = (Vmax [S]) / (Km + [S])
Our gut wall essentially has a “speed limit”: we can only absorb so much glucose–the starting molecule for cellular respiration, our biological process of creating usable energy–per hour. Specifically, SGLT1, the glucose transporter in our body, has a maximum saturation rate of around 60 grams per hour. Yet, once again, scientists have found a way to surpass this.
Fructose, another simple sugar, has its own gateway: GLUT5.
Accounting for the previous requirements of Activation Energy (Ea) and Osmotic Pressure (Π), it’s been found that a ratio of two Glucose to one Fructose, or the less common but equally effective one Glucose to 0.8 Fructose (essentially the same ratio), allows for an additional 30 grams per hour of saturation overall. That is a whopping 50 percent increase per hour!
THE ULTIMATE STRATEGY, ON A BUDGET
“So, what’s the play?”
Obviously, the best solution is to give your body as many carbohydrates as possible, but that’s hard and, more importantly, economically costly. The average 90g of carbs can cost around 7-14 dollars per hour. Over 6 hours for a 50k, the starter ultra-distance, which is around 63 dollars, on top of the few-hundred-dollar race fee.
If working on a budget–as is the case for many college students–it is best to “save the best for the last.” By that logic, eat regular foods with complex carbohydrates early on. At this stage, you still have water to spare, and the Splanchnic Shunt hasn’t fully taken effect. As the run progresses, transition to specialized nutrition to cut costs in half. With this in mind, making sure to hydrate well is critical, since cellular respiration and digestion both require water, as do most other bodily functions; all of this goes to waste if you don’t hydrate!
If you aren’t working on a budget, great! You can go right ahead and order large quantities of your favorite sports nutrition and rock those immediately; it is definitely more efficient.
Eat, Run, Repeat.
