For decades, athletes and weekend warriors alike have been told to “carb-load” before strenuous activity – pasta dinners, energy gels, and sugary drinks consumed in large quantities to fuel their performance. However, a new scientific review, synthesizing over 100 years of research from 160+ studies, challenges this long-held belief. The findings suggest that sustained energy during exercise relies more on stable blood glucose levels than simply maximizing muscle glycogen stores.
The Myth of Glycogen and the Reality of Glucose
Traditional sports nutrition has focused on maximizing glycogen – the stored form of carbohydrates in muscles – believing that depletion is the primary cause of fatigue. While glycogen certainly plays a role, the review demonstrates that fatigue in prolonged exertion is more closely linked to declining blood glucose. The brain relies on glucose to function, and when levels drop, it signals the body to conserve energy, leading to perceived exhaustion.
This doesn’t mean carbohydrates are unnecessary. Instead, it highlights the importance of consistent glucose availability. Small, regular carbohydrate intake during exercise – as little as 15-30 grams per hour (roughly half a banana or 15 grapes) – appears more effective at stabilizing blood sugar than a large pre-event meal.
Why This Matters: Beyond Athletic Performance
The implications extend beyond elite athletes. The review arrives at a critical time: one in three U.S. adults has prediabetes, and 81% are unaware of it. Surprisingly, even endurance athletes aren’t immune; studies show that up to 30% may unknowingly have prediabetic conditions.
Large carbohydrate binges can cause rapid spikes and crashes in blood sugar, potentially increasing the risk of insulin resistance over time. The research suggests that a more balanced approach – small, steady carbohydrate intake during activity – may be more sustainable for both performance and metabolic health.
A Nuanced Perspective
This doesn’t invalidate low-carb or ketogenic diets for everyday life. Instead, it acknowledges that carbohydrates can be strategically used to support energy stability during periods of high demand. The body’s ability to produce glucose from other sources (gluconeogenesis) has limits. When activity exceeds the liver’s capacity, carbohydrates become crucial.
Ultimately, the science supports a personalized approach. There’s no “one-size-fits-all” strategy. Whether you’re an athlete, a casual exerciser, or simply interested in optimizing your energy levels, understanding the role of blood glucose is key.
The latest research underscores that carbohydrates aren’t inherently “good” or “bad.” Their value lies in how they’re used: not as a fuel to be depleted, but as a tool to maintain energy stability and prevent performance-limiting drops in blood glucose.
