A new wave of sports-nutrition research is challenging fixed carbohydrate rules, as endurance athletes increasingly use individualized testing to determine exactly how much fuel their bodies can absorb and burn.

For years, endurance athletes were given relatively straightforward nutritional advice: consume enough carbohydrates before competition, replenish glycogen stores and, during long events, aim for a prescribed number of grams per hour.

That formula is now being rewritten.

One of the most significant emerging trends in sports nutrition in 2026 is the rise of personalized carbohydrate fueling — an approach that treats an athlete’s ability to absorb and metabolize carbohydrates as an individual physiological characteristic rather than something that can be determined solely from generic guidelines.

The shift has gained new momentum following the launch in August of FuelSync, a laboratory-based test developed by sports-nutrition researchers at the University of Birmingham. The system measures how much carbohydrate an athlete actually converts into usable energy while exercising, potentially allowing cyclists, runners, triathletes and other endurance competitors to tailor race nutrition far more precisely.

The concept addresses a problem that has become increasingly visible at the highest levels of endurance sport.

Athletes know that carbohydrates are a critical fuel during prolonged exercise. Consume too little and performance can deteriorate as readily available energy declines. Consume too much, however, and the digestive system may struggle to cope, producing bloating, nausea, cramping or other gastrointestinal problems that can ruin a race.

Until recently, athletes largely managed that balance by following standardized recommendations and gradually experimenting during training.

New research suggests the difference between individuals may be far greater than previously assumed.

In the research underpinning the Birmingham testing system, endurance-trained participants consumed carbohydrate at the same rate — 90 grams per hour — during prolonged exercise. Yet the amount their bodies actually oxidized varied dramatically. Some used approximately 49 grams per hour, while others converted as much as 81 grams per hour into energy.

That variation means two athletes following precisely the same nutrition plan may be receiving very different physiological benefits.

For one competitor, 90 grams per hour could be close to an effective fueling strategy. For another, much of that carbohydrate may provide little additional performance benefit while increasing the possibility of gastrointestinal distress.

According to the University of Birmingham, individual optimal intake could differ by as much as 25 percent above or below conventional guideline-derived estimates.

The finding reflects a broader transformation in elite sports nutrition.

Carbohydrates are making a comeback

The new enthusiasm for carbohydrate optimization is particularly striking because popular diet culture spent much of the previous decade moving in the opposite direction.

Low-carbohydrate, ketogenic and high-fat diets became influential among recreational athletes, with advocates arguing that training the body to rely more heavily on fat could provide a virtually inexhaustible energy supply during long-distance exercise.

The scientific debate has continued, but the current consensus in elite endurance sport remains strongly favorable toward making carbohydrates available when high performance is required.

A major 2026 scientific debate published in The American Journal of Clinical Nutrition concluded that strategies designed to ensure sufficient carbohydrate availability remain the best-supported approach for optimizing endurance performance, particularly when athletes must sustain higher exercise intensities.

The question at the cutting edge of sports nutrition is therefore increasingly not whether athletes should consume carbohydrate, but how much each athlete should consume and when.

That distinction is producing increasingly sophisticated strategies.

The race toward 120 grams an hour

Traditional endurance-sport recommendations have commonly suggested carbohydrate intakes of up to around 90 grams per hour during events lasting more than roughly 2½ to three hours.

Professional athletes, however, have increasingly pushed beyond that ceiling.

Cyclists, marathon runners and ultra-endurance competitors have experimented with intakes approaching 120 grams per hour, while some athletes have reportedly attempted 150 grams or even more.

A major review published this year in The Journal of Nutrition noted that real-world endurance athletes have experimented with intakes ranging from 120 to 200 grams per hour, although scientific evidence does not yet support such extreme quantities as a universal recommendation.

The research suggests that approximately 120 grams per hour may be physiologically achievable for some trained athletes, particularly when glucose and fructose are combined in formulations that use different intestinal transport mechanisms.

But researchers increasingly caution against turning 120 grams into the new 90.

The emerging philosophy is that the highest possible intake is not necessarily the optimal intake.

Rather than asking how much carbohydrate an athlete can force the digestive system to tolerate, sports scientists are beginning to ask how much carbohydrate that particular athlete can actually absorb, oxidize and convert into useful energy.

Measuring fuel through breath

Personalized testing attempts to provide that answer scientifically.

The Birmingham protocol uses carbohydrates containing a naturally traceable carbon isotope known as carbon-13. Athletes consume a carbohydrate drink while running or cycling at a controlled intensity, and researchers analyze samples of their breath.

Because carbon dioxide produced when the ingested carbohydrate is metabolized contains the carbon-13 marker, scientists can calculate how much of the fuel the athlete is actually oxidizing.

The FuelSync assessment involves approximately two and a half hours of sustained exercise, with athletes consuming carbohydrate at regular intervals while respiratory samples are collected.

The result is effectively a metabolic fingerprint of the athlete’s fueling capacity.

Professor Gareth Wallis, an exercise metabolism and nutrition specialist at Birmingham who developed the system with Exeter University researcher Tim Podlogar, argues that the approach can help athletes avoid both under-fueling and unnecessary overconsumption.

That could be particularly valuable in sports where tiny differences in performance determine results.

From the laboratory to the Tour de France

Elite cycling is already becoming one of the clearest demonstrations of this new nutrition philosophy.

During the 2026 Tour de France, performance nutrition specialists described increasing use of personalized fueling strategies tailored not simply to individual riders but to individual stages, expected intensity, weather conditions and tactical demands.

Rather than consuming identical quantities every day, riders may alter carbohydrate intake depending on whether they are facing a flat sprint stage, a long mountain stage or a relatively low-intensity recovery day.

Nutrition planning is increasingly being integrated with power-meter data, estimated glycogen depletion and other physiological information.

In other words, diet is becoming part of the athlete’s performance-data ecosystem.

The same analytical mentality that transformed training through heart-rate monitors, GPS systems, power meters and continuous physiological monitoring is now moving into nutrition.

The gut is becoming trainable equipment

Another important development is the recognition that an athlete’s digestive system itself can be trained.

Regularly consuming carbohydrate during exercise can improve tolerance to larger quantities and potentially increase the intestine’s ability to transport carbohydrates.

Elite endurance athletes therefore increasingly practice their race-day nutrition during training rather than treating food and drink as something separate from physical preparation.

The phrase frequently used by sports nutritionists is “train the gut.”

Just as runners progressively condition their muscles to tolerate marathon distance, they may also condition their gastrointestinal system to process repeated carbohydrate intake while running at race intensity.

That has helped create an entirely new category of performance preparation in which gels, drinks and carbohydrate mixtures are tested as carefully as shoes, bicycles or aerodynamic equipment.

Glucose alone may no longer be enough

The composition of carbohydrate intake is also changing.

Recent studies have strengthened evidence that mixtures of glucose and fructose can allow athletes to oxidize more externally consumed carbohydrate than glucose alone because the two sugars use partially different absorption pathways in the intestine.

Research published in The Journal of Nutrition in July found higher exogenous carbohydrate oxidation when athletes consumed glucose and fructose together compared with glucose alone.

This helps explain why many modern endurance products increasingly contain carefully engineered combinations of sugars rather than simply large quantities of glucose.

For manufacturers, that means sports nutrition is evolving from a relatively simple market of energy drinks and gels into something closer to applied metabolic engineering.

The danger of copying professionals

The trend nevertheless carries an important warning for amateur athletes.

If professional cyclists begin consuming 120 grams of carbohydrate per hour, recreational runners may assume that doing the same will automatically improve their performance.

That conclusion would miss the central point of the emerging research.

Elite athletes often reach high intake levels only after years of endurance training and deliberate gastrointestinal conditioning. Their workloads, energy requirements and metabolic characteristics are also considerably different from those of most recreational competitors.

Even the scientific literature remains cautious. Researchers reviewing ultra-high carbohydrate strategies in 2026 have warned that evidence supporting intakes well beyond established recommendations remains limited and that aggressive fueling strategies should not automatically be generalized to every athlete.

Personalization, rather than maximization, is becoming the more important principle.

Sports nutrition enters the precision era

The trend also reflects a wider movement throughout health and fitness.

Wearable devices already attempt to personalize sleep, recovery and training intensity. Continuous glucose monitors have entered recreational sport. Algorithms analyze running mechanics and cycling power. Genetic tests and metabolic assessments promise increasingly individualized recommendations.

Nutrition is now moving in the same direction.

Instead of a diet being defined simply as “high carbohydrate,” “low carbohydrate” or “high protein,” athletes may increasingly receive fueling prescriptions based on their own metabolic response.

A future marathon plan might therefore resemble a training program: a specific carbohydrate target for each hour, different glucose-to-fructose ratios, fluid and sodium targets, and adjustments according to temperature, intensity and duration.

For elite sport, the attraction is obvious.

Once equipment, training and recovery have been optimized to extraordinary levels, nutrition represents another frontier where marginal gains remain available.

For recreational athletes, the implications may eventually be equally significant as sophisticated testing becomes cheaper and more accessible.

The latest sports-nutrition trend therefore represents something larger than another dietary fashion.

After years in which athletes debated whether carbohydrates were good or bad, sports science is moving toward a more nuanced question:

How much carbohydrate is right for this particular athlete, performing this particular event, at this particular intensity?

The answer increasingly appears to be different for everyone.

And in modern endurance sport, that difference may eventually be measured not in grams alone, but in seconds at the finish line.