“Eat early and often.” For decades, this mantra has dominated the advice given to endurance runners, instilling the belief that more fuel equals better performance. From carbo-loading rituals the night before races to the incessant ingestion of gels, bars, and electrolyte drinks during events, the fear of running out of energy—“bonking”—has shaped how runners approach nutrition.
But have we taken it too far? Overfueling, while less dramatic than underfueling, is increasingly recognized as a significant problem in endurance sports. From nausea and cramps to long-term metabolic inefficiency, the consequences of overeating on the run can be just as detrimental as running on empty.
In this article, we’ll break down the myth of constant fueling, explore the science of energy balance during exercise, and help you understand when—and how much—you actually need to eat to perform at your best.
The concept of "hitting the wall" has become one of the most feared experiences in long-distance running. Glycogen, the body’s carbohydrate reserve, is finite. When it’s depleted, performance declines sharply, leaving runners fatigued, mentally foggy, and struggling to continue. This fear drives many runners to consume large amounts of food during races, aiming to "stay ahead" of glycogen depletion.
However, this narrative oversimplifies energy dynamics. While glycogen depletion is real, the body has multiple energy systems that work in tandem. It’s not an all-or-nothing scenario, and fueling doesn’t need to be constant to prevent disaster.
The sports nutrition industry capitalized on this fear. Gels, chews, and drinks have been marketed as essential tools for performance, with instructions to consume them every 20–30 minutes. While these recommendations have some basis in science, they’re often generalized for all runners, ignoring individual needs and race contexts.
Amateur runners often model their fueling strategies after elites. When Eliud Kipchoge consumes precise carbohydrate drinks during his record-breaking marathons, it’s easy to assume the same will work for recreational runners. However, elite runners operate at intensities and metabolic rates that most of us never reach, making their fueling needs vastly different.
The body relies on a combination of glycogen (carbohydrates), fat, and to a lesser extent, protein to fuel exercise. The proportion of each depends on factors like intensity, duration, and training status.
The most immediate consequence of overfueling is stomach trouble. When you consume more calories than your digestive system can process during exercise, undigested food sits in the gut, leading to bloating, cramping, nausea, and diarrhea.
Overloading on high-sugar products can cause rapid insulin spikes, followed by energy crashes. This creates a rollercoaster of performance, where you feel strong momentarily but struggle to maintain consistent effort.
Consistently relying on external fuel can blunt the body’s ability to utilize fat efficiently. Over time, this creates a dependency on constant carbohydrate intake, making bonking more likely when fuel isn’t readily available.
For recreational runners, overfueling can lead to consuming more calories than burned during training, potentially contributing to weight gain over time.
Fueling is highly individual. Factors like body weight, pace, metabolic efficiency, and race conditions all play a role in determining how much energy you need to consume.
This strategy involves training in a low-carb or fasted state occasionally to enhance fat oxidation, while still consuming carbs on race day to maximize performance. Studies in The Journal of Applied Physiology (2016) show that fat adaptation can improve metabolic flexibility, allowing athletes to perform well with less frequent fueling.
Kipchoge consumes around 60–90 grams of carbs per hour during marathons, but his strategy is meticulously planned. He trains his gut to tolerate this intake, and his body’s metabolic demands at world-record pace are vastly higher than the average runner’s.
Ultrarunner Zach Bitter follows a low-carb, high-fat diet, relying primarily on fat for energy during long, steady efforts. He supplements with small amounts of carbs during races, balancing metabolic efficiency with the need for quick energy.
Fueling during long runs and races is essential, but more isn’t always better. By understanding your body’s needs, experimenting with fueling strategies, and avoiding the temptation to overconsume, you can optimize performance while minimizing the risks of gastrointestinal distress and energy crashes.
Remember: the goal isn’t to eat as much as possible—it’s to fuel efficiently and effectively. Listen to your body, train your gut, and trust in your preparation.