What Experts Want You to Know About High-Carb Fueling

What Experts Want You to Know About High-Carb Fueling

For decades, the standard advice for endurance athletes has been straightforward: eat carbohydrates before and during prolonged exercise to maintain blood glucose levels and delay fatigue. Despite periodic surges in popularity of low-carbohydrate and ketogenic approaches, the scientific consensus remains clear that carbohydrate availability is a primary determinant of endurance performance. A 2020 review in the British Journal of Sports Medicine reaffirmed that carbohydrate intake before and during exercise improves performance in events lasting longer than 90 minutes.

The mechanistic rationale is well established. During prolonged exercise, muscle glycogen stores become progressively depleted, and blood glucose levels decline. Exogenous carbohydrate intake maintains blood glucose concentrations and sustains high rates of carbohydrate oxidation, allowing athletes to maintain their target intensity. Without adequate carbohydrate fueling, athletes experience a well-documented decline in power output and increased perception of effort.

Despite the strength of this evidence, a significant gap exists between what the research recommends and what many athletes actually do. Survey data consistently shows that a substantial proportion of endurance athletes fail to meet recommended carbohydrate intake during training and competition. Some of this gap can be attributed to the persistent marketing of low-carbohydrate and ketogenic approaches for endurance performance, which have found a receptive audience among athletes looking for a competitive edge or experiencing gastrointestinal distress with traditional fueling products.

The practical recommendations are straightforward. For events lasting longer than 90 minutes, athletes should aim to consume 30 to 60 grams of carbohydrate per hour, increasing to up to 90 grams per hour for events exceeding two and a half hours. This can be achieved through a combination of sports drinks, gels, chews, and whole food sources such as bananas or dates. Individual tolerance varies considerably, and athletes should practice their fueling strategy during training rather than experimenting on race day.

What about the argument that training with low carbohydrate availability enhances metabolic adaptations? There is some evidence that periodized carbohydrate availability, strategically training some sessions with low glycogen, can upregulate fat oxidation pathways. However, this approach is best reserved for specific training sessions rather than adopted as a full-time strategy, and should be implemented under the guidance of a sports nutrition professional. The consensus view is that low-carbohydrate training has a place in a periodized program but is not superior to adequate carbohydrate fueling for overall performance outcomes.

The bottom line: high-carbohydrate fueling is well supported by the evidence. Athletes concerned about gastrointestinal issues, weight management, or metabolic flexibility should work with a sports dietitian to develop an individualized plan rather than abandoning carbohydrate intake entirely. The science has not changed, regardless of what the latest diet marketing campaign claims.