Ultra-High Carbohydrate Intake During Training and Racing
Background
Current sport nutrition guidelines recommend consuming 60-90 grams of carbohydrates per hour to fuel endurance performance. There are various individual factors that influence whether an athlete chooses to consume closer to 60 grams or at the higher end of 90 grams per hour of carbohydrates. Research literature has long-suggested that there are no additional benefits to consuming more than 90 grams per hour. Consuming more than this has been associated with increased GI discomfort as well due to the body’s limited ability to digest and absorb such large quantities of carbohydrates during endurance exercise.
A recent trend in endurance sport, particularly among professionals, has been to consume ultra-high carbohydrate (U-HC) intakes in training and racing, which is defined as consuming >90 grams of carbohydrates per hour (2). It seems like it is more commonplace today to see professional triathletes consuming 90-120 grams per hour in both training and racing. These athletes have also been objectively very successful, with athletes like the Norwegian trio being known to consume U-HC in training and racing and being some of the best triathletes in the world. There are other high-level triathletes and runners doing the same, consuming U-HC and winning some of the biggest races in their respective sport.
However, U-HC intake has been informed more by anecdotal evidence and less by scientific research. In other words, because some professionals started consuming U-HC have had recent success, more and more professionals and amateurs have tried to replicate this in an effort to “keep up” with the latest trend out of a fear of missing out on potential performance improvements. Plews and colleagues (2) recently published a paper reviewing the available research on this exact topic and discussed their findings. Before we dig into their findings, let’s start by covering the basics on carbohydrate intake during exercise.
The Benefits of Carbohydrate Intake on Endurance Performance
Carbohydrates play a critical role in fueling endurance performance. While endurance exercise (e.g., training and racing) is largely an aerobic sport in which the body relies heavily on the breakdown of fat as fuel, carbohydrates still provide a meaningful amount of fuel to support endurance exercise, even at lower exercise intensities. From an Ironman-distance triathlon to an all-out mile time trial, carbohydrates are essential to performance. As the duration of the event gets longer, however, consuming carbohydrates becomes critical in supporting performance as the body only stores a finite amount of carbohydrate in the form of glucose in the blood and glycogen in muscle and liver tissue. As the duration of an endurance event goes beyond a few hours, or as the intensity of an endurance event rises, supplying the body with carbohydrates helps maintain blood glucose levels and helps spare muscle and liver glycogen stores. Maintaining blood glucose levels helps ensure both cognitive and physical performance is maintained, and sparing glycogen stores helps make these stores last deeper and deeper into an endurance event before they are completely depleted.
Many endurance athletes are well aware of the impact of being low in blood glucose or depleted in their available glycogen stores (i.e., the dreaded “bonk”). Research has demonstrated that 60-90 grams of carbohydrates is the sweet spot for the majority of athletes in maintaining glucose availability to fuel performance while simultaneously avoiding an increased risk of GI issues from consuming too much (1). This recommendation has been around for decades now. With recent trends shifting to U-HC intakes of >90 grams per hour, is there new scientific evidence to support this shift?
What does recent research say about U-HC?
As mentioned previously, Plews et al (2) dug into the research available on this topic and discussed their findings. Firstly, the authors aimed to answer the question: “Does consuming >90 grams of carbohydrates per hour improve measured performance in a research setting?” Well, according to their findings, not really. Authors discussed the findings of various studies and meta-analyses that found the benefits of consuming more than 90 grams of carbohydrates per hour did not reliably translate to improved endurance performance, served to blunt fat breakdown (i.e., oxidation) while increasing carbohydrate oxidation, and paradoxically seemed to accelerate the rate of liver and glycogen depletion. Additionally, some research has found that consuming more than 90 grams of carbohydrates per hour only served to increase the proportion of ingested carbohydrates that were not absorbed into the bloodstream. In other words, the human body simply excreted these additional carbohydrates beyond 90 grams per hour rather than absorbing them into the bloodstream to be used as fuel and spare glycogen stores.
The next logical question then is: “Well then why do U-HC intakes seem to be associated with performance success among some elite endurance athletes?”. Plews and colleagues discussed some of these potential mechanisms but highlighted the fact that these mechanisms have not been validated in research studies to date. Therefore, the following are only hypothesized mechanisms as to the benefits of U-HC intake:
1. Carbohydrate breakdown is more oxygen-efficient than fat breakdown
The oxidation of carbohydrates requires less oxygen per liter than the oxidation of fat to yield the same energy output. Put simply, an athlete oxidizing carbohydrates at a greater rate from U-HC intake is more efficient when compared to a lower carbohydrate oxidation rate. U-HC intake has been shown to blunt fat oxidation and increase carbohydrate oxidation. This improved efficiency allows for a lower oxygen consumption rate for a given performance output, potentially explaining why some elite athletes are performing so well with U-HC intakes in racing. They can race at the same intensity prior to U-HC intake, but more efficiently and at a lower oxygen cost. However, this alone does not mean overall performance will be better as performance is influenced by many factors working in synchrony on race day. Despite the potential to improve exercise efficiency, there were notable drawbacks to U-HC intake discussed in the previous paragraphs that could negate this benefit.
2. Improved lactate metabolism
Many athletes and coaches still believe that lactate production is detrimental to performance. However, lactate production is not what causes fatigue and is a normal metabolic by-product of carbohydrate oxidation. If lactate production and/or clearance is not sufficient to meet energy demands of exercise, the accumulation of Hydrogen ions in the muscle is the cause of fatigue. Lactate production helps to buffer these hydrogen ions and lactate can be shuttled to highly aerobic muscle tissue during exercise and be utilized in energy production. U-HC intakes may allow for up-regulation of lactate being shuttled to active muscle tissue to be oxidized for energy. In turn, this may fuel improved performance. Among highly trained professional endurance athletes, this impact may be more readily realized compared to amateur athletes with less lactate shuttling capabilities. Again, however, this is theoretical and has not been verified with current experimental research.
3. Carbohydrate-induced perception of effort improvement
It has been shown that carbohydrate intake, and even just rinsing the mouth with a carbohydrate solution, can lower perceived effort via the reward center in the brain. The sweetness of carbohydrates signals to the brain that energy is coming and can have effects that result in an improved perception of effort. This has mainly been demonstrated in shorter and higher-intensity endurance performance or under carbohydrate-depleted conditions. Nonetheless, this could be a potential mechanism to explain improved performance with U-HC intakes.
Conclusions
In summary, there is no current evidence to support the general recommendation for endurance athletes to have U-HC intakes during training and racing. The current recommendation for consuming 60-90 grams of carbohydrates per hour is the gold standard, evidence-based recommendation for endurance athletes. While there is a recent trend for professional athletes towards consuming >90 grams of carbohydrates per hour, the possible benefits they are realizing may not be translatable to the everyday amateur or age group endurance athlete. Unique individual differences due to genetics or their elite level of endurance conditioning may allow them to “get away” with U-HC intakes that confer some performance benefit. Alternatively, there may not be any performance benefit to U-HC intake at all, and it is a trend that will fade with time. For now, my personal recommendation would be to avoid copying the pros and stick to what we know works well for most athletes based on the available evidence.
References:
1. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Nutrition and athletic performance. Med Sci Sports Exerc, 48(3), 543-568.
2. Plews, D. J., Booth, P. D., Krieger, T., & Maunder, E. (2026). Fuelled or Fooled? Examining the Evidence and Mechanisms Behind Ultra-High Carbohydrate Intake in Endurance Athletes. Sports Medicine, 1-22.
Happy training and racing!
-Ryan Eckert, MS, CSCS