"Food is Fuel" – Why proper fueling is absolutely essential?

Ferenc Soma Kovács, national record holder middle-distance runner

 

The cliché in the title is often encountered in conversations among athletes, and in books and videos on sports nutrition. Although the saying has become quite trite by now, it still expresses a fundamental truth: our body provides the energy (ATP) needed for movement by oxidizing macronutrients (primarily carbohydrates and fats) consumed through food. This is precisely why proper fueling plays a crucial role before, during, and after long-distance endurance competitions – such as marathon and ultra-running, open water swimming, long-distance cycling races, and Ironman. Fortunately, the advancements of our current era enable the highest possible level of fueling in these demanding disciplines.

Consider that in the 1980s, excellent marathon runners would minimize their carbohydrate intake for a few days during the week preceding their marathon races, thereby completely depleting their glycogen stores. In practice, this meant that for several days they consumed almost exclusively protein and fat-rich foods – mainly various meats. However, in the last two to three days before the race, their diet was characterized by very high carbohydrate intake. This so-called supercompensation process resulted in muscles being "overloaded" with glycogen. However, this extreme Scandinavian method came at a high price: runners were tired and irritable; their performance was explicitly poor in the first few days of "starvation."

Naturally, the carbohydrate loading protocol discussed above is quite outdated today, and athletes simply consume more carbohydrates during the last week before a race, alongside reduced training volume. In addition, sports nutrition science has also developed significantly; scientists have found solutions to countless previously unanswered mysteries, so the number of blind spots in science has dramatically decreased since the 2000s. With the advancement of science, the market has naturally kept pace: new dietary supplement products have appeared that were able to eliminate problems previously considered insoluble. The arsenal of these competing products has significantly expanded due to fierce market competition.

Let's take a look at the history of fueling in long-distance endurance competitions. Before 2004, athletes primarily relied on maltodextrin (glucose). Since the maximum saturation level of SGLT1 glucose transport in the small intestine was 60 grams per hour, any higher intake caused serious intestinal problems. Consequently, the science of sports nutrition considered energy depletion, often referred to as "hitting the wall" among athletes, to be inevitable.

Between 2004 and 2010, pioneering research by Dr. Asker Jeukendrup shed light on the so-called 2:1 glucose-fructose ratio, which activated the GLUT5 fructose transporter. This dual-source carbohydrate model then made possible an hourly carbohydrate absorption rate of 90 grams, representing a significant, fifty percent extension of the former 60 gram per hour limit.

However, the real breakthrough came between 2016 and 2018 with the hydrogel revolution. A company called Maurten developed and patented a special process that combined carbohydrates with alginate and pectin. The essence of the process was that as soon as the drink powder reached the acidic region of the stomach, the compound formed a protective hydrogel casing, allowing the drink powder to pass into further regions of the intestine without being detected by intestinal receptors. Alongside the emergence of carbon-plated racing shoes, which offered a significant mechanical advantage, this was undoubtedly the other major catalyst behind Eliud Kipchoge's sub-two-hour marathon performance in 2017. Maurten hydrogel enabled carbohydrate absorption of over one hundred grams per hour.

The appearance of hydrogel triggered an endless cascade in the field of optimizing sports gels. In 2020, we entered the era of "extreme 1:0.8 carbohydrates." Companies such as Nduranz, Precision Fuel & Hydration, and Neversecond developed a 1:0.8 maltodextrin-fructose ratio that effortlessly allowed the absorption of 120-140 grams of carbohydrates per hour.

Presentation of the Research

However, the reader might rightly ask whether the explosive development in fueling technology has had any impact on elite athletes? And if so, to what extent? Well, to answer this question, I conducted a small research study. I was curious about the extent to which world records in long- and ultra-distance running improved between 2000 and 2023. I wanted to prove whether the two main factors leading to performance improvement – the appearance of carbon-plated running shoes and hydrogels – clearly coincided with the temporal improvements. Of course, I am aware that other factors, such as the refinement and optimization of training methods, as well as the emergence and spread of high-tech recovery tools, can also be considered potential causes behind the improving trend of world records. Nevertheless, in long-distance running and ultra-running, I attribute less significance to the factors listed above, as the positive changes in training methods after 2000 were primarily evident in short- and middle-distance running. Consider the spread of the Norwegian double threshold method, which is hardly used by the world's best in their 50 and 100 km preparations. Furthermore, the latter two events are not part of the Olympic program, meaning that ultra-runners training for them certainly do not prepare in modern Olympic training camps where a complete range of high-tech recovery tools would be at their disposal. The discipline – with a few exceptions – is largely represented by amateur athletes who cover the costs of their recovery tools from their own budgets. Thus, after due consideration, the other independent variables mentioned above can be considered irrelevant.

Research Methodology

In my research, I examined the development curve of running world records between 2000 and 2023 for both genders across four different race distances: 10, 42.195, 50, and 100 kilometers. I designated the year 2000 as the baseline year. I expressed the development of world records as a percentage relative to this baseline year.

Research Results

Looking at the graphs above, we can establish the following clear facts:

• At 10 kilometers: Around 2010, both genders achieved a 2% improvement compared to the world record in effect in 2000. This stagnated for a long time, then for women, in the year of the carbon-plated running shoes' appearance, this improvement rate doubled to 4%. In the new fueling era, it was possible to push this slightly above 4%. In subsequent years, it approached 6%. For men, carbon-plated shoes brought nearly a 4% improvement, but hydrogel brought none. For women, the extent of the first world record improvement after the appearance of carbon-plated shoes is roughly the same as the extent of world record improvement achieved in the new fueling era. The same is not observed for men.
• In the marathon: A total of sixteen world records have been broken since 2000, significantly exceeding the number of records set at 10 kilometers in the same period (10). The world of athletics reached a point around 2014 where the 2000 record was surpassed by at least 2% in both genders; by 2022, this was at least 4%. In the marathon by 2023, although not by much, overall a greater improvement in world records was achieved in both genders than at 10 kilometers. For women, the extent of the first world record improvement after the appearance of carbon-plated shoes is slightly greater than the extent of world record improvement demonstrated in the new fueling era. For men, the two values are approximately equal.
• At 50 kilometers: Both revolutionary innovations brought improvement, but the spread of extreme 1:0.8 carbohydrates brought by far greater gains. For women, the extent of world record improvement achieved in the new fueling era is approximately four and a half times greater than the extent of world record improvement after the appearance of carbon-plated shoes. For men, this multiplier is approximately threefold.
• At 100 kilometers: For women, no improvement occurred at all during the examined period, while for men, extreme 1:0.8 carbohydrates and carbon-plated shoes induced similar degrees of improvement.

Interpretation of Results and Conclusion

Overall, for both genders, it can be stated that world records set in the new fueling era resulted from record-breaking performances that were at least as great – but rather greater – than those induced by carbon-plated shoes. With the exception of 100 kilometers, women generally achieved greater improvements thanks to the new fueling formulas than men. In other words, women benefited more from the development of fueling gel technology. In the marathon and at 50 kilometers, the improvement compared to previous years was significantly more pronounced in the new fueling era than at 10 kilometers.

How does Polar FuelWise™ help in practice?

As the data clearly shows, appropriate quality and quantity of carbohydrate intake is now at least as critical a factor for peak performance (especially in marathon and ultra distances) as physical fitness itself or the latest carbon-plated wonder shoes. Hydrogels and extreme 1:0.8 ratio fuels theoretically allow for the absorption of 90-120 grams of carbohydrates per hour, but practical implementation often presents serious challenges for both amateur and professional athletes.

The biggest problem is not what to eat, but when and how much. During a long training session or race, with an elevated heart rate, accumulating fatigue, and narrowing mental focus, people tend to forget to refuel. And when we already feel the lack of energy or the approach of the dreaded "wall," it's usually too late – glycogen stores are depleted, blood flow to the stomach is minimized, so a sudden large intake of carbohydrates, instead of being absorbed, only causes stomach problems and cramps.

This is where sports technology comes in, specifically Polar FuelWise™'s intelligent fueling assistant. The FuelWise™ feature (available in Polar watches like the Vantage, Grit X, or Pacer series) is a repeating timer that alerts the athlete to refuel again with beeps at certain intervals.

The Smart Carbs Reminder feature is what makes Polar truly special. Before a training session or race, you enter the following parameters into the watch:

• The planned training time (e.g., 3 hours 30 minutes).
• The planned intensity (based on heart rate zones).
• The carbohydrate content of one serving of the gel or sports drink you intend to use.

And the watch – based on your previous training data, physical parameters (weight, age, gender, VO2max), and planned intensity – calculates approximately how much carbohydrate you will need to complete the distance. The genius of the watch lies in the fact that the device monitors your heart rate and actual energy expenditure in real time. If you run at a higher intensity than expected (e.g., into a strong headwind or uphill), your body burns carbohydrates faster. FuelWise™ detects this and automatically increases the frequency of fueling reminders. However, if you slow down and stay in the fat-burning zone, the reminders become less frequent.

When the time comes, the watch vibrates, and a clear message appears on the display: "Consume carbohydrates (X g)!" This way, you will never make the mistake of forgetting to eat, and you can replenish the energy used according to your current, real intensity.

Post-Workout Analysis 

The Polar ecosystem (Polar Flow) has another huge advantage in making fueling more conscious. After completing a workout, the watch not only shows the number of calories burned but also the proportion of energy your body derived from carbohydrates, fats, and proteins. During high-intensity interval training or in the first half of a marathon, you will see that up to 80-90% of the energy came from carbohydrates. In contrast, during a slow, recovery run, this ratio shifts towards fats. Breaking down burned calories into macronutrient sources thus makes conscious replenishment after training a breeze.