Breaking the Ceiling of Carbohydrate Oxidation During Exercise: New Research on 120g/h with a Glucose-Fructose Blend

This article is based on peer-reviewed research from international sports science journals, providing an in-depth analysis of the impact of “exogenous carbohydrate oxidation” on athletic performance, and combining it with Taiwan’s local cycling and race scenarios to offer actionable training nutrition recommendations.

The success or failure of prolonged endurance exercise often hinges not on engine size, but on fuel supply. Traditional sports nutrition textbooks have long stated the iron rule that “the human body can oxidize at most 60 grams of exogenous carbohydrates per hour,” with anything beyond that accumulating in the gut and causing gastrointestinal distress. However, over the past fifteen years, a series of isotope-tracking studies originating from Asker Jeukendrup’s laboratory have completely rewritten this ceiling. By mixing glucose and fructose in specific ratios and leveraging two independent intestinal transport pathways, exogenous carbohydrate oxidation rates have been pushed to 90 g/hr, 105 g/hr, and even an astonishing 120 g/hr observed in a 2022 trail-running study. For athletes tackling Wuling Climb, 226 ultra-triathlons, or 100-kilometer trail races, this means “hitting the wall” is no longer an inevitability.

In Taiwan’s endurance sports community—whether it’s climbing enthusiasts heading west up Wuling, long-distance riders heading east through the Huadong Rift Valley, or participants in Sun Moon Lake loop rides, Taroko Marathon, and 226-kilometer ultra-triathlons—the topic of “exogenous carbohydrate oxidation” matters because it directly determines whether you can maintain pace in the latter stages of an event, avoid cramping and hitting the wall, and recover effectively between consecutive training days. Many amateur athletes pour all their effort into power training and equipment upgrades while overlooking nutrition—this “free margin of improvement.” In fact, when training volume and equipment are comparable, the quality of nutritional strategy is often the key variable separating finishing from dropping out, and personal bests from collapse. This article will walk you through the complete context—from cellular molecular mechanisms and randomized controlled trial evidence to dose-response curves and practical application—debunking long-standing myths so that your fueling strategy is truly built on science.

Academic Research Review

Regarding the scientific exploration of “exogenous carbohydrate oxidation,” top international journals have accumulated rich and rigorous evidence. Below are several representative studies selected for their value in methodological design, sample populations, and strength of conclusions, which together construct our current understanding of this topic:

1. Jeukendrup AE et al. (2004, Journal of Applied Physiology) used ^13C stable isotope labeling to compare a glucose-only drink with a glucose+fructose mixed drink, finding that the mixed drink’s exogenous oxidation rate was approximately 40% higher than glucose alone.

2. Jentjens RL and Jeukendrup AE (2005, British Journal of Nutrition) confirmed that at a glucose:fructose ratio of 2:1, the exogenous carbohydrate oxidation rate could reach 1.26 g/min (approximately 75 g/hr), breaking the 60 g ceiling.

3. Viribay A et al. (2020, Nutrients) administered 120 g/hr of maltodextrin+fructose to mountain trail runners, finding that the high-dose group had significantly lower muscle damage markers (CK, myoglobin) and faster recovery.

4. King AJ et al. (2022, Medicine & Science in Sports & Exercise) used a randomized crossover design to confirm that 120 g/hr was well tolerated in trained athletes while maintaining higher power output.

Looking across these studies, it becomes clear that the scientific picture of “exogenous carbohydrate oxidation” is not a single fixed conclusion but has been continuously revised and deepened as research methods have advanced. Early studies predominantly used laboratory-controlled time trials or exhaustion tests, while subsequent research progressively incorporated stable isotope tracking, muscle biopsies, functional magnetic resonance imaging (fMRI), and molecular biomarkers, allowing us to move from “phenomenon observation” to “mechanistic explanation.” It is worth noting that most high-quality studies employ randomized crossover designs, where each subject serves as both experimental and control, substantially reducing noise from individual differences. However, extrapolation of research conclusions still requires caution: the responses of trained subjects in the laboratory may not fully translate to general amateur athletes; and the effects of a single acute intervention may not equate to long-term chronic adaptation. When reading the “effect sizes” and “statistical significance” of these studies, we must also distinguish between “statistically significant” and “practically meaningful”—a 1% improvement might determine medal placement in elite competition, but its significance is relatively limited for recreational riders.

Core Mechanisms

The key lies in two transport proteins on the small intestine’s brush border: glucose is absorbed via SGLT1 (sodium-glucose cotransporter), while fructose travels through the GLUT5 channel. When glucose is consumed alone in large quantities, SGLT1 becomes saturated at approximately 60 g/hr, and excess sugar滞留 in the intestinal lumen causes osmotic diarrhea and bloating. Adding fructose provides a second “parallel” highway via GLUT5, allowing total absorption to stack. Fructose is converted to glucose or lactate in the liver before being used by muscles—though this adds a metabolic step, it effectively unloads the burden on SGLT1.

To truly understand how “exogenous carbohydrate oxidation” affects athletic performance, one must return to physiology at the cellular and systemic levels. Athletic performance is the result of multi-system coordination: the cardiovascular system handles oxygen and fuel delivery, muscle cells handle energy conversion and mechanical contraction, the central nervous system regulates motor unit recruitment and fatigue perception, while the gut and liver form the hub of nutrient absorption and metabolism. The reason the aforementioned mechanisms translate into measurable performance differences is precisely because they act on one (or multiple) critical links in this chain. The table below organizes the key points of action at different physiological levels for this topic, helping you build a complete mechanistic picture:

| Level of Action | Key Mechanism | Significance for Athletic Performance |

|—|—|—|

| Cellular/Molecular | Affects mitochondrial efficiency, enzyme activity, and signal transduction | Determines the efficiency of energy conversion and adaptive direction |

| Muscle Tissue | Regulates substrate utilization, buffering capacity, and contractile function | Affects sustainable power output and fatigue onset |

| Systemic Integration | Alters blood flow distribution, thermoregulation, and hormonal environment | Determines stability and safety during prolonged exercise |

| Central Nervous System | Regulates fatigue perception, drive, and motor unit recruitment | Affects “how tired it feels” and the ability to persevere |

Particular emphasis should be placed on the two dimensions of “dose-response” and “temporal dynamics.” The same nutritional intervention, at different intake amounts and different timing, can produce vastly different or even opposite effects—this is precisely why many mainstream recommendations are one-sided. Only by understanding the mechanisms can we judge “under what circumstances to use it, how much, and when,” rather than blindly following trends.

Furthermore, the limiting factors of athletic performance shift dynamically with exercise intensity and duration: in short, high-intensity efforts, limitations often stem from the phosphagen system and the accumulation of glycolytic byproducts; in multi-hour endurance events, limitations shift toward the combined effects of glycogen depletion, rising core temperature, fluid and electrolyte imbalance, and central fatigue. The reason “exogenous carbohydrate oxidation” deserves in-depth exploration is precisely because it can specifically target certain of these limiting factors. This also reminds us that no nutritional strategy can be evaluated in isolation from the “exercise context”—a fueling rhythm suited to a 40-minute criterium may not apply to a 6-hour climbing epic, and vice versa. The more thoroughly you understand the mechanisms, the more flexibly you can adjust across different event formats, rather than rigidly adhering to a fixed formula. This ability to “adapt to context” is precisely the dividing line between amateur athletes and those who truly understand sports science.

Dose-Response Relationship

In sports nutrition, “the dose determines both the toxicity and the benefit.” Doses that are too low fail to reach the physiological threshold and yield nothing; doses that are too high may trigger side effects, gastrointestinal distress, and even interfere with training adaptations in the opposite direction. The table below summarizes the dose-response relationship for “exogenous carbohydrate oxidation” and serves as the most important quantitative reference when designing a personal fueling plan:

Dose / Condition	Applicable Scenario	Key Recommendations
< 30 g/hr	Low intensity / < 1 hour exercise	Single-source glucose is sufficient; no mixing required
30–60 g/hr	1–2 hours moderate intensity	Glucose or maltodextrin; 2:1 mixing not necessary
60–90 g/hr	2–3 hours long-distance	Glucose:fructose 2:1; requires gut training
90–120 g/hr	> 2.5 hours high-intensity events	Maltodextrin:fructose 1:0.8; mandatory 4–6 weeks of prior gut training

As the table shows, the benefit often follows an “inverted U-shaped” or “threshold-plateau” curve: effectiveness increases with dose until the effective threshold is reached, but beyond a certain plateau, there is not only no additional benefit—the marginal costs (side effects, gastrointestinal burden, financial expense) rise sharply instead. This means “finding your own optimal dose” matters far more than “eating as much as possible.” It is recommended to progressively test different doses during training (not on race day), recording subjective feelings, gastrointestinal responses, and power data to build your own dose profile. Remember: the laboratory average is a starting point, not the endpoint; each person’s body weight, metabolic rate, gut tolerance, and genetic background will shift the optimal dose in an individualized way.

Differences Across Populations

The benefits of “exogenous carbohydrate oxidation” are not equal for everyone. Age, sex, training status, body size, and genetic background all significantly modulate the magnitude of individual responses. Ignoring these differences and applying a one-size-fits-all recommendation is one of the most common mistakes in sports nutrition.

Population Dimension	Response Characteristics	Practical Recommendations
Beginners vs. Advanced	Advanced athletes have more mature physiological adaptations; responses are often more stable but with smaller marginal gains	Beginners should start conservatively at low doses and build tolerance first
Male vs. Female	Body weight, hormonal cycles, and sweat composition differ, affecting dose and requirements	Females should individualize by body weight and pay attention to iron and energy availability
Young vs. Older	Older individuals often experience reduced absorption efficiency and anabolic resistance	Older individuals may need higher doses or better timing
Body Size Differences	Body weight directly affects the absolute amount calculated per mg/kg or g/kg	Always convert to a dose corresponding to individual body weight; avoid copying general rules

When interpreting “individual differences,” one must also be wary of a common statistical pitfall: studies mostly report “group average responses,” but beneath the average often lies enormous individual variability. In the same intervention, some may be strong responders, some non-responders, and some even negative responders. This is why, even when a study shows that something is “effective on average,” you still need to confirm through your own trials which category you fall into. The recommended approach is to conduct personalized A/B testing: in two training sessions with conditions as similar as possible, adopt or omit the strategy respectively, compare power, heart rate, and subjective feelings, and repeat several times before drawing conclusions. This empirical spirit of “using yourself as the sample” is the essential path from group science to a personal prescription.

Taking Taiwan’s common amateur endurance population as an example, many are middle-aged cyclists over 35 who train around work commitments. This group simultaneously faces declining recovery speed, insufficient sleep, and time pressure, so the “return on investment” of nutritional strategies is often higher than for young elites—meaning that correct nutritional intervention can yield relatively greater room for improvement. Female athletes, in particular, need to pay close attention to the effects of the menstrual cycle on metabolism and requirements, as well as whether energy availability is sufficient, to avoid falling into the low energy availability (LEA) trap while pursuing lighter body weight. After understanding population differences, you will realize: truly professional nutritional advice is always an individualized prescription that varies from person to person, not a one-size-fits-all slogan.

Practical Training Application

Theory must ultimately be translated onto the training plan and the race course. Below is a practical framework for converting “exogenous carbohydrate oxidation” into concrete training and race-day operations:

• Pre-race testing principle: All nutritional strategies must first be rehearsed in training; “never try anything new on race day” is an iron rule. Gut tolerance to new fueling products takes time to build.

• Periodization mindset: Align nutritional strategies with the training cycle—the base phase can emphasize adaptation-oriented strategies, while the pre-season shifts to performance-oriented fueling optimization.

• Progressive introduction: Start with low doses and low frequency, adjust gradually based on bodily responses, and build a personalized dose and timing profile.

• Data tracking: Combine power meter data, heart rate, subjective fatigue (RPE), and gastrointestinal comfort records to objectively evaluate whether an intervention is truly effective.

• Holistic context: Nutrition is one part of training, sleep, recovery, and psychology; a single supplement cannot compensate for sleep deprivation or flawed training design.

Using a one-week training schedule as an example, it is recommended to rehearse different fueling scenarios in the key high-intensity sessions of the week (such as threshold intervals or repeated climbs) and the weekend long ride: high-intensity days focus on rapid energy supply and central activation, while long-distance days focus on sustained energy delivery, gut tolerance, and recovery. Through repeated rehearsal, the body can execute the optimal fueling rhythm “automatically” on race day, leaving mental resources for pacing and tactical decisions. Remember, the goal of a nutritional strategy is not theoretical perfection, but stable reliability under the fatigue, heat, and pressure of a real race course.

The most common mistake many people make when executing a nutrition plan is “being serious only on race day while eating carelessly during regular training.” This is precisely putting the cart before the horse: regular training is the best laboratory for building gut tolerance, testing doses, and cultivating fueling rhythm. If you hope to execute an 80 g/hr carbohydrate intake on race day, you must rehearse it repeatedly in training until your body becomes accustomed to it; if you want to rely on a certain supplement, you must confirm during training that it is genuinely effective for you and free of side effects. It is recommended to integrate a nutrition log with your training log, recording the fueling content, intake timing, gastrointestinal responses, and performance data for each key session. After weeks to months of accumulation, the value of this personalized database will far exceed any generic nutrition guide. Additionally, do not overlook the often-underestimated “post-training recovery fueling”—the quality of recovery between consecutive training days often determines whether you can steadily accumulate training volume without injury, and training volume is the most fundamental engine of long-term progress. Treat nutrition as a serious part of training rather than a last-minute accessory before race day, and your progress curve will look noticeably different.

Local Application in Taiwan

Taiwan’s unique climate, terrain, and race culture add localized considerations to the application of “exogenous carbohydrate oxidation.” Taiwan’s summer is hot and humid, with apparent temperatures often exceeding 35°C; sweat rates and fluid/electrolyte losses are far higher than the research conditions of temperate countries, meaning that hydration and fueling recommendations from foreign literature often need to be “revised upward.” In events like the Westbound Wuling climb, which ascends from sea level to 3,275 meters, the appetite suppression at altitude, low temperatures, and prolonged exercise duration pose a severe test for energy planning.

Regarding local fueling options, Taiwan’s abundant bananas, sweet potatoes, pineapples, sports drinks, and convenience store ready-to-eat foods can all be incorporated into fueling strategies; the extremely high density of convenience stores also makes mid-ride refueling on long-distance rides relatively easy. It is recommended that Taiwanese cyclists, when planning classic routes such as Sun Moon Lake, Wuling, Beiyi, Buyan Pavilion, and the Eastbound route, survey fueling points along the way in advance and strengthen sodium and fluid intake in response to Taiwan’s humid and hot environment. Athletes in the Taroko Marathon, Taipei Marathon, and triathlon events across the island should likewise incorporate the above local climate factors into their individualized nutrition plans to perform at their best under subtropical conditions.

Common Myth-Busting

Myth: Popular belief holds that “the more sugar you eat, the faster you run,” but if you force 120 g/hr without gut training, the unabsorbed sugar will only trigger diarrhea. The key finding from research is the “trainable absorption ceiling,” not “unconditionally more is better.”

This type of myth spreads widely often because it “sounds reasonable,” is easy to pass along by word of mouth, or is amplified by marketing hype. Yet the value of science lies precisely in testing intuition with rigorous evidence: many ideas that seem self-evident fail to hold up under randomized controlled trials. Sports nutrition, in particular, is rife with oversimplified “silver bullet” messaging that compresses complex dosing, timing, and individual differences into a single slogan. The next time you hear a dogmatic nutrition claim, it’s worth asking: “What is the level of evidence behind this statement? Who is the target population? Are the dose and timing clearly specified?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for amateur athletes moving toward scientific training.

Conclusion

“Exogenous carbohydrate oxidation” is a topic in sports nutrition that combines both theoretical depth and practical value. From the academic evidence reviewed in this article, its benefits are real, but it is by no means an unconditional silver bullet—the key lies in correct dosing, appropriate timing, individualized adjustments, and synergy with overall training, recovery, and sleep. For endurance sports enthusiasts in Taiwan, while grasping the scientific principles, it is equally important to integrate local climate, terrain, and race characteristics to turn general principles into a personalized prescription that suits oneself. May every rider sweating on Wuling, in the rift valleys, or along the island-circumnavigation route break through their limits through science-based nutrition strategies and enjoy the pure joy that sport brings. Before you next step onto the race course, don’t forget—your bottle holds not just water and sugar, but an entire validated system of sports science.

Related Reading

• Carbohydrate Oxidation Rate Ceiling: The Scientific Basis of the 90g/hr Dual-Source Strategy
• 90 or 120 Grams of Carbs Per Hour on Race Day? Interpreting the Latest Intake Ceiling
• Research Review: Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Recent Academic Literature Review and Training Practice (Article 1294)
• Research Review: Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Study of Elite Athletes’ Physiological Characteristics (Article 1135)