A practical framework for fueling that explores the history and science of race nutrition to help you understand the products on the shelf, turning confusion into confidence.
It starts with a wall of brightly colored gels and drink mixes, each promising endurance in a pouch. Runners swear by their favorites, but few can explain why they work—or don’t. Matt and Molly pull back the curtain on the science and history behind those packets, turning a maze of sugar ratios, salt counts, and gut grumbles into something you can actually understand. They examine why some products seem to love you while others ruin your race, practically breaking down the make up of different products out there, and what the science actually says about how our bodies use all this stuff.
Episode Description:
In this episode of Legwork, Matt and Molly take on one of running’s most confusing topics: fueling. They trace how we went from ancient “performance foods” to modern gels and drink mixes, and why understanding what’s inside those packets can make all the difference.
Together, they cover:
- How fueling evolved from ancient rituals to modern sports science
- The difference between energy systems — carbs, fats, and how the body actually uses them
- What “isotonic,” “hypertonic,” and “2:1 ratios” really mean, and how those formulas affect absorption and gut comfort
- Why some products upset your stomach while others don’t
- How to approach carb loading and in-race fueling more strategically
- The myths and mistakes that keep runners underfueled
- And how to navigate the wall of options on the shelf with more confidence
Along the way, they share personal fueling mishaps (including Matt’s maple syrup era), laugh through gut science, and translate complex research into clear, practical insight.
Whether you’re training for your first half marathon or trying to shave minutes off a PR, this episode will help you understand what your body needs — and fuel smarter for whatever’s next.
Bakline's Race and Training Fuel Selector: https://docs.google.com/spreadsheets/d/1u7Rh8LWrgB_9B3kKKpKMwTEnqXyRcc0js1UYw4vwTCg/edit?usp=sharing
References:
- Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008 Feb;40(2):275-81. doi: 10.1249/mss.0b013e31815adf19. PMID: 18202575.
- Sedlock DA. The latest on carbohydrate loading: a practical approach. Curr Sports Med Rep. 2008 Jul-Aug;7(4):209-13. doi: 10.1249/JSR.0b013e31817ef9cb. PMID: 18607222.
- Arnall, D.A., A.G. Nelson, J. Quigley, et al. Supercompensated glycogen loads persist 5 days in resting trained cyclists. Eur. J. Appl. Physiol. 99:251Y256, 2007.
- Jeukendrup, A.E. Training the Gut for Athletes. Sports Med 47 (Suppl 1), 101–110 (2017). https://doi.org/10.1007/s40279-017-0690-6
- W Larry Kenney,Jack H Wilmore,David L Costill. Physiology of Sport and Exercise 8th Editions
Full Show Notes
00:00 – Introduction, Matt's Fueling Eras, and Why This Episode Matters
Matt and Molly open episode seven of Legwork with a topic that every runner wrestles with: how to fuel properly. They aren’t nutritionists—and they’re quick to say so—but they aim to demystify how nutrition products work, why certain strategies fail, and how runners can think more critically about what they consume during training and racing.
Matt reflects on his many “fueling eras,” from GU packets and maple syrup to homemade honey concoctions. He admits that, early on, nutrition wasn’t even on his radar—until he learned the hard way through fatigue and injury, including a sacral stress fracture linked to underfueling.
Their early conversation sets the theme for the episode: understanding fueling not just as a race-day variable, but as a key part of training, recovery, and injury prevention.
Takeaways:
- Nutrition isn’t just for race day—it’s central to consistent training and recovery.
- Many runners underfuel early in their careers because they don’t yet feel its limits.
- The right approach to fueling is both scientific and deeply personal.
09:08 – Agenda for the Episode
Molly outlines how they’ll tackle a notoriously confusing topic by layering the discussion from first principles to practical applications.
They’ll cover:
- A brief history of nutrition and fueling in sport.
- How the body’s energy systems actually work.
- How products are formulated around those systems.
- Guidance on what to use, when, and how much.
- Carb loading and troubleshooting common problems.
Matt frames the goal: to help listeners think methodically about fueling without getting lost in pseudo-science or one-size-fits-all advice.
Takeaways:
- The aim isn’t to prescribe products but to explain how and why they work.
- Fueling science has patterns and logic—once you understand them, product choices make more sense.
- There’s a difference between dietary nutrition and athletic fueling.
10:00 – Historical Perspectives on Nutrition and Performance
Molly takes listeners back to the 1920s, when Harvard researchers drew blood at the finish line of the Boston Marathon to measure glucose levels and discovered a link between blood sugar and fatigue.
From ancient warriors eating animal organs to “carb loafing” in the 1980s, the conversation traces how ideas about performance fuel have evolved—from mystical beliefs to scientific trial and error.
Matt adds color with the role of World War–era nutrition experiments (and Snickers bars as proto–energy bars). The conversation weaves together physiology, social attitudes, and even the amateur ethos of early sport, when training science was viewed almost as cheating.
Takeaways:
- Protein was long believed to be the best performance fuel until mid-century research proved otherwise.
- The development of Gatorade in the 1960s marked the start of modern sports nutrition.
- The concept of carb loading emerged in the 1970s and has been refined ever since.
16:09 – The Evolution of Sports Training and Nutrition
They connect scientific breakthroughs to cultural shifts—how postwar research, Olympic experimentation, and endurance booms pushed nutrition from superstition to science.
The duo laughs over the brief, forgotten 1980s trend of “carb loafing,” which meant eating normally while tapering (and doing no workouts). It didn’t work—but the term deserves a comeback.
Takeaways:
- Every era of training science mirrored broader social changes—from industrialization to the rise of amateur athletics.
- By the 2000s, sports fueling became more data-driven, focusing on absorption and gut tolerance rather than calories alone.
- Despite better science, modern athletes still struggle with misinformation and overwhelm.
20:06 – Understanding Energy Systems: Carbs
Molly explains how glycogen—the stored form of carbohydrates—powers most endurance performance. The pair break down how intensity determines which fuel the body prefers: at slower paces, fat dominates; once you cross roughly 60% of VO₂ max, glycogen takes over.
They unpack why “the fat-burning zone” is misleading and why running too fast on easy days sabotages aerobic development.
Takeaways:
- Glycogen powers anything over ~60% VO₂ max—so most racing is carb-dependent.
- Easy running trains the body to use fat more efficiently, which supports long-term endurance.
- Depleting glycogen too far delays recovery and raises injury risk.
29:22 – Understanding Energy Systems: Fats
Fat oxidation is slow but powerful—like a diesel engine compared to glycogen’s turbo mode. Molly explains why fat is vital for endurance but too slow for high-intensity racing.
They discuss how women’s physiology allows slightly greater fat reliance and why slow-twitch athletes differ from fast-twitch ones in fueling needs.
Takeaways:
- Easy running develops the “fat factory”—more mitochondria for efficient energy use.
- Women may have a small advantage in fat utilization and pacing longevity.
- Fast-twitch athletes burn through glycogen faster and may need more frequent fueling.
40:15 – The Impact of Carbohydrates on Performance
They tackle the myth of “fat adaptation” as a sustainable performance strategy. While it’s possible to train the body to use more fat, it caps speed and limits glycogen efficiency.
Molly emphasizes that even slower marathoners are working at high relative effort—so everyone needs carbs, regardless of pace.
Takeaways:
- Fat adaptation has limits; glycogen remains essential for marathon and faster efforts.
- Effort, not pace, determines fuel usage—slower runners aren’t exempt from carb needs.
- Fueling adequately during training prevents low-energy injuries and better supports recovery.
47:07 – How Nutrition Products Reflect These Energy Systems
The conversation shifts from biology to the shelf. Nutrition companies design products based on how carbs and electrolytes move through the body. Molly explains the key sugar types (glucose and fructose) and how using both in tandem increases absorption rates—one relies on sodium, the other doesn’t.
Takeaways:
- Most products mix glucose (or maltodextrin) and fructose to bypass absorption bottlenecks.
- Sodium levels determine how well glucose can cross cell membranes.
- Training with the same fuel you race with helps the gut adapt and improves absorption.
49:27 – Understanding Sugar Ratios in Sports Nutrition
They decode the mysterious “2:1” and “1:0.8” ratios on fuel labels—what they mean, how they affect GI comfort, and why brands like Maurten, GU, and Honey Stinger differ so much.
Matt jokes about discovering maltodextrin in his own smoothie while Molly explains why “natural” fuels like honey or maple syrup are less optimized but more palatable.
Takeaways:
- 2:1 glucose-to-fructose fuels are classic, stable, and generally easier on the gut.
- 1:0.8 ratios maximize carb absorption but can increase GI risk.
- “Natural” fuels are often 1:1 and may work well if balanced with salt and water.
55:21 – Isotonic vs. Hypertonic Fuels: What You Need to Know
They introduce another key distinction: isotonic (pre-diluted, like Maurten or Science in Sport) versus hypertonic (concentrated, like GU or Huma).
Matt confesses to misunderstanding isotonic labeling—thinking he didn’t need extra water—and realizes why his race-day strategy once failed.
Takeaways:
- Isotonic = balanced with body fluids; no extra water required, but lower salt.
- Hypertonic = more concentrated; must be taken with water or absorption suffers.
- No single product provides carbs, salt, and water perfectly—you must build a system.
01:04:49 – Carbohydrate Requirements for Endurance Events
They get quantitative: 30g/hour for short events, 60g/hour for marathons, up to 90g/hour for ultras—with corresponding sodium needs (300–600mg/hour).
They explain how absorption caps at ~60–90g/hour depending on sugar ratios and how dehydration or under-salting can make gels feel “sloshy.”
Takeaways:
- Fueling rates scale with duration and intensity.
- Every gel ≈ 25–30g carbs and 100 calories—most runners need 2–3 gels per hour plus water.
- Separate carb and salt sources if you prefer flexibility (e.g., gels + electrolyte tablets).
01:13:17 – The Importance of Carb Loading Before Races
Carb loading, they clarify, is not about a single pasta dinner. It’s a multi-day strategy tied to muscle glycogen replenishment. Molly explains gender differences: men can substitute carbs for other macronutrients, but women often need to increase total calories to see performance benefits.
Matt shares his infamous “Philadelphia Marathon 2023” story of overdoing it—ice cream, pizza, mashed potatoes, and Naked Juice in one night—with predictable GI disaster.
Takeaways:
- Start carb loading right after your final hard workout—muscles absorb best then.
- One to three days of loading is sufficient; the day before the race should be light.
- Women may need to increase calories by ~30% to see full glycogen benefits.
- Liquid carbs (Maurten 320, Naked Juice, Coke) help reduce volume and ease digestion.
01:28:03 – Troubleshooting Nutrition Issues During Races
They close by addressing the most common fueling problems:
- Texture aversion: try chews or isotonic liquids.
- Sloshy stomach: may be low sodium, not “too much water.”
- GI distress: could stem from poor timing, dehydration, or a mismatch in carb ratios.
The final reminder: there’s no universal fix—and “not fueling” is never the answer. Runners should experiment, train with their chosen products, and understand why something does or doesn’t work.
Takeaways:
- Identify whether your issue is absorption, hydration, or taste—not all GI issues are equal.
- Think of fueling as a modular system: carbs + salt + water, not a single product.
- Gut training and product awareness are key to race-day success.
