Why the 10g Carbohydrate Theory Fails: What the Science Really Says About Carbs, the Brain, and Fatigue
- Annie Bothma
- 4 days ago
- 5 min read
~ Annie Bothma, Endurance Athlete, Sports Nutritionist (MSc), Running & Strength Coach
On The Real Science of Sport Podcast on the 16th of October 2025, sports scientist Dr Ross Tucker dissected a provocative claim recently shared by Professor Tim Noakes — that athletes might need only 10 grams of carbohydrate per hour to sustain endurance performance.
Dr Tucker, one of South Africa’s most renowned voices in the scientific space, offered a nuanced, physiology-based critique. His discussion echoed what decades of research have already demonstrated: endurance performance depends on complex, integrated regulation between the brain, muscles, and metabolic systems, not on a single variable like blood glucose.
This blog draws on that discussion — and the broader scientific literature — to explain why the 10 g/hour hypothesis fails and what athletes actually need to know about fueling with carbohydrates for optimal performance and longevity in the sport as an athlete.
The Theory in Question
The new hypothesis argues that fatigue occurs when the brain senses falling blood glucose. Supposedly, a minimal glucose trickle — around 10 g per hour — is sufficient to sustain endurance performance. According to Tim Noakes and colleagues, their new theory proposes “fatigue is all in the brain,” and as long as you can “keep the brain happy,” you can prevent fatigue.
While elegant in its simplicity, this view neglects the reality that fatigue is multifactorial. It arises from coordinated feedback among the central nervous system, muscular metabolism, thermoregulation, cardiovascular strain, and psychological perception of effort.
Reducing carbohydrate intake to this minimal amount disrupts this balance rather than optimizing it. Just because you can doesn’t mean you should!
Fatigue Is an Integrated Safeguard
Fatigue protects the body from catastrophic failure. The brain continuously monitors:
Blood glucose and hepatic glycogen — fuel for the central nervous system.
Muscle glycogen — local energy needed for muscle contraction.
Core temperature, hydration, oxygen delivery, and sodium balance.
When any of these systems approach danger, the brain lowers motor drive to preserve homeostasis. Adequate carbohydrate intake provides reassurance to the brain that energy reserves are secure, delaying this protective slowdown. Insufficient carbohydrate intake — such as 10 g/h — signals vulnerability and triggers fatigue sooner (Abbiss & Laursen, 2005; St Clair Gibson & Noakes, 2004; Noakes, 2012).
Why the “Brain-Only” Model Fails
Dr Tucker notes that Noakes’ argument contradicts his own earlier data showing that higher carbohydrate availability slows the rise in rating of perceived exertion (RPE) and prolongs time to exhaustion (Coyle et al., 1986). When carbohydrate is limited, RPE climbs steeply, and performance drops even if blood glucose appears “normal.”
The brain functions best when it perceives abundance rather than scarcity.
What the Scientific Evidence Actually Shows
Research consistently demonstrates that carbohydrate requirements scale with exercise duration and intensity.
For events lasting between 1 and 2.5 hours, ingesting around 30–60 grams of carbohydrate per hour is sufficient to maintain plasma glucose levels and delay the onset of fatigue (Coyle et al., 1986).
During longer sessions of 2.5 hours or more, higher intakes of approximately 60–90 g per hour — ideally from multiple transportable carbohydrate sources such as glucose and fructose — enhance endurance capacity and reduce gastrointestinal discomfort (Jeukendrup & Moseley, 2010).
In ultra-endurance events, where energy demands are extreme and prolonged, athletes can benefit from consuming up to 90–120 g of carbohydrate per hour to maximize carbohydrate oxidation, sustain cognitive performance, and support overall race intensity (Jeukendrup & Moseley, 2010; Burke et al., 2017).
No peer-reviewed study has demonstrated equivalent performance at 10 g per hour. At such low intake, muscle glycogen depletes rapidly, RPE rises, and both power and pace decline (Coyle et al., 1986).
Carbohydrates, the Brain, and Efficiency
From a metabolic standpoint, carbohydrates remain the most oxygen-efficient fuel for high-intensity exercise. Adequate carbohydrate availability supports sustained neural drive, stable perceived effort, and higher training quality. When carbohydrate intake is restricted — such as limiting intake to 10 g per hour — the body is forced to rely more heavily on fat oxidation, which is slower and more oxygen-demanding, leading to earlier fatigue and reduced race-pace capacity (Burke et al., 2017; Jeukendrup & Moseley, 2010).
Real-World Fueling Practices
Elite marathoners, cyclists, and long-course triathletes routinely fuel at aggressive carbohydrate intake rates — often 90 to 120 g of carbohydrate per hour from blended sources like glucose and fructose — to sustain race-level intensity, protect cognitive function late in competition, and delay the rise in perceived effort. These high-intake strategies have been repeatedly shown to improve long-duration endurance performance and gut tolerance (Jeukendrup & Moseley, 2010), and attempts to adhere to a low-carb dietary approach at the elite level increase oxygen cost and compromise race-pace output (Burke et al., 2017).
If you want to see peak performance, you have to look at what the top in the sport are doing — they are pushing the upper limits of carbohydrate intake to keep the fire burning hot and maintain the highest level of intensity and performance. There will always be outliers and those that succeed despite their habits, not because of them! However, the vast majority of the top endurance athletes are consuming carbohydrates during training and racing —and a lot more than 10 g per hour!
The Verdict
The idea that “10 g/h is enough” is scientifically indefensible. It misrepresents the central-governor concept, overlooks decades of performance data, and contradicts the very research it cites.
In reality:
Fatigue is anticipatory and multifactorial.
The brain allows sustained performance only when energy supply feels secure.
Adequate carbohydrate (60–120 g/h) reassures the brain, maintains muscle drive, and optimizes both metabolic and cognitive performance.
Cutting intake to 10 g/h doesn’t prevent fatigue — it provokes it earlier. Optimal endurance performance demands a fueling enough to sustain all physiological systems—not just the brain!
This position is supported by controlled laboratory trials in endurance athletes (Coyle et al., 1986), systematic reviews and performance studies of carbohydrate intake (Jeukendrup & Moseley, 2010), randomized adaptation studies in elite race walkers (Burke et al., 2017), and foundational models of fatigue regulation (Abbiss & Laursen, 2005; St Clair Gibson & Noakes, 2004; Noakes, 2012).
Conclusion
Peak performance requires proper fuel. You can’t train intensely, adapt, recover, and maintain high performance without adequate nutrition. What matters is consistency over a long period of time. Personal bests and records are built over months of stacking bricks. Progress is made through training blocks consisting of quality workouts and long endurance sessions. Relying on just 10 g per hour won’t cut it in this sport — you won’t last long!
References
Abbiss, C. R., & Laursen, P. B. (2005). Models to explain fatigue during prolonged endurance cycling. Sports Medicine, 35(10), 865–898. https://doi.org/10.2165/00007256-200535100-00004
St Clair Gibson, A., & Noakes, T. D. (2004). Evidence for complex regulation of human exercise performance: The integration of the neural and metabolic systems. British Journal of Sports Medicine, 38(6), 797–806. https://doi.org/10.1136/bjsm.2003.009852
Noakes, T. D. (2012). Fatigue is a brain-derived emotion that regulates the exercise behaviour to ensure the protection of whole-body homeostasis. Frontiers in Physiology, 3, 82. https://doi.org/10.3389/fphys.2012.00082
Coyle, E. F., Coggan, A. R., Hemmert, M. K., & Ivy, J. L. (1986). Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Journal of Applied Physiology, 61(1), 165–172. https://doi.org/10.1152/jappl.1986.61.1.165
Jeukendrup, A. E., & Moseley, L. (2010). Multiple transportable carbohydrates enhance gastric emptying and fluid delivery. Scandinavian journal of medicine & science in sports, 20(1), 112–121. https://doi.org/10.1111/j.1600-0838.2008.00862.x
Burke, L. M., Hawley, J. A., Jeukendrup, A. E., Morton, J. P., Stellingwerff, T., & Maughan, R. J. (2017). Adaptation to a low-carbohydrate, high-fat diet: Effects on exercise metabolism and endurance performance in elite race walkers. Journal of Physiology, 595(9), 2785–2807. https://doi.org/10.1113/JP273230
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