Sports nutrition science has advanced significantly in recent years. Today, we clearly understand what makes a difference in a gel and what does not. In this article, we present the 6 criteria that guide Z2 Performance’s product development and that should guide any serious decision when choosing or prescribing a carbohydrate gel.
1. Different carbohydrate sources make all the difference
The most important criterion in a gel is not flavor, but where the carbohydrate comes from. The intestine absorbs different types of carbohydrates through different pathways. When a gel uses only one source, that pathway becomes overloaded, part of the energy is not absorbed, remains in the intestine, and causes cramping, bloating, and nausea. This is one of the most common causes of gastrointestinal distress during races.
The solution is to combine different sources that use parallel absorption pathways, such as glucose and fructose. This allows the intestine to absorb more carbohydrates per hour without overloading any single pathway. The most recent research indicates that the ideal ratio between these two sources is close to 1:0.8. This differs slightly from the old 2:1 standard, as this newer combination improves both absorption and gastrointestinal comfort.
Gels with maltodextrin as a single source are outdated technology from the 1990s. Well-formulated blends allow intake of 90 to 120 grams of carbohydrates per hour with much lower risk of gastrointestinal issues, which is crucial in long-distance events. However, there is a third dimension that most people ignore: the energy release curve over time.
This is where isomaltulose comes in as the third source in the Z2 blend. It is a natural carbohydrate with a more stable molecular structure, digested more slowly and gradually. Its glycemic index is 32, much lower than maltodextrin’s 85. In practice, this means it does not cause sharp spikes and crashes in energy, instead providing a more sustained glucose release over time. This becomes especially valuable in the final stages of a race, when energy stores are depleted and glycemic stability can determine whether an athlete maintains pace or breaks down.
Studies support this. In a clinical trial with 20 cyclists (König et al., 2016), those who consumed isomaltulose showed more stable blood glucose levels during exercise, increased fat oxidation sparing glycogen, and performed better in the final time trial compared to those consuming only maltodextrin. A second study with runners (JISSN, 2021) confirmed the same pattern: more stable glycemia, lower insulin spikes, and no difference in gastrointestinal comfort. Tolerance was comparable to other carbohydrate sources.
For this reason, the Z2 blend uses a 2:1:1 ratio (maltodextrin, fructose, and isomaltulose). Each plays a different role over time: maltodextrin provides rapid energy in the first minutes after ingestion; fructose uses a parallel intestinal pathway, increasing total absorption capacity without overloading a single route; and isomaltulose sustains energy delivery in the mid and late stages of the race, when glycogen levels begin to drop. Three sources. Three time windows. One gel that supports performance from start to finish.
2. Consistency and formulation matter
Many athletes arrive well-trained at a race but fail to finish due to gastrointestinal issues. Cramping, nausea, and that persistent feeling of a full stomach all have a cause. A gel that is too concentrated or poorly formulated takes longer to be absorbed, remains in the stomach, and causes discomfort exactly when energy is most needed. This is not bad luck. It is poor formulation.
A gel’s formulation must match the intestine’s absorption speed during exercise. Isotonic gels, meaning those with a concentration similar to body fluids, are absorbed more quickly and with much lower risk of discomfort. A practical benefit is that you do not necessarily need to consume water alongside it. This is particularly important in situations where water is not readily available, such as during a cycling descent or in the middle of a trail run.
There is also an important factor that changes how gels should be prescribed: the intestine adapts. The more you practice carbohydrate intake during training, the greater your tolerance during competition. This means gels should be introduced in training, never tested for the first time on race day. For nutritionists and physicians, this has direct implications: digestive preparation begins weeks before the event, not the day before.
3. Flavor and taste fatigue determine how much you can tolerate
Liking the flavor of a gel may seem trivial, but it has a scientific component that directly affects performance. If you get tired of the product mid-race, you stop consuming it. And stopping intake when you still have hours of effort ahead is a serious problem. Flavor is not just personal preference, it is part of the fueling strategy.
Science refers to this as Sensory-Specific Satiety, or taste fatigue. It occurs when the body begins to reject something that was previously enjoyable simply due to repetition. Very sweet or intense flavors tend to accelerate this fatigue. Athletes relying on strongly flavored gels are more likely to struggle with intake in the later stages of a race.
Studies show that in the first 60 minutes of exercise, athletes prefer sweeter flavors. After that, preferences shift toward more neutral or slightly salty profiles. Gels with milder flavor profiles perform better over time, allowing continued consumption when it matters most, without resistance.
4. Sodium beyond replacement
Most people associate sodium with replacing what is lost through sweat. That is true, but it is only part of the story. Sodium plays an active role in glucose absorption in the intestine, acting as a co-transporter. Without it, glucose uptake becomes less efficient. In practical terms, a gel without adequate sodium delivers less usable energy, even with a perfect carbohydrate formulation.
Additionally, sodium enhances water absorption in the intestine, meaning it supports hydration while also aiding energy delivery. In long events and hot conditions, where sweat losses are higher, a gel with insufficient sodium can compromise both energy and hydration simultaneously.
The optimal sodium amount varies depending on sweat rate, exercise intensity, and environmental conditions. At Z2, sodium is treated with the same level of importance as carbohydrates in formulation.
5. Caffeine: dose and timing make all the difference
Caffeine is the most studied supplement in sports nutrition, with consistent evidence showing improved endurance performance. The ideal dose does not need to be high. Moderate doses, used at the right time, provide the same benefits as high doses without the side effects: increased heart rate, nervousness, irritability, and gastrointestinal discomfort.
Caffeine primarily acts on the brain, reducing the perception of effort, making you feel less fatigued than you actually are. This effect is most valuable in the final stages of a race, when mental fatigue becomes a limiting factor. Therefore, the optimal strategy is not to consume caffeine from the start, but to reserve it for critical moments: a climb during a run, the final segment of a cycling leg, or the sprint to the finish line. Non-caffeinated gels early on, caffeinated gels strategically later.
Gels containing very high doses of caffeine per unit, above 200 mg, reduce flexibility and increase the risk of cumulative effects during long events. The ideal design uses moderate, effective doses that allow flexibility within a fueling strategy.
6. Packaging as a strategic factor
Packaging is often treated as an aesthetic decision. This is a mistake. Imagine opening a gel with sweaty hands, at 170 beats per minute, while maintaining your running pace. If the packaging does not facilitate this, part of the effort is wasted. The best formula in the world does not work if it does not reach the body at the right time.
What truly matters in packaging: the ability to open it with one hand; appropriate volume per serving, not too small requiring multiple gels per hour, and not too large making it difficult to consume quickly; and consistency stability in heat, since gels that become too liquid or too thick at high temperatures negatively affect intake.
At Z2, these criteria are part of the validation protocol, treated with the same rigor as formulation parameters. Because a perfect gel on the inside is useless if it fails at the most critical moment: when the athlete needs it most.
Choosing or prescribing a carbohydrate gel is a technical decision, even if it seems simple. The six criteria presented here are not elite-level demands, they are the minimum any serious product should meet. Where the carbohydrate comes from, how the intestine responds, whether the flavor sustains intake throughout the race, whether sodium is correctly dosed, whether caffeine is strategically designed, and whether the packaging works in practice. All of this directly impacts the final outcome.
At Z2, each of these criteria has a specific answer in every product in the lineup. Not because it is trendy, but because the science is clear, and ignoring it has a real cost: the athlete who could have finished stronger, faster, or simply finished.
References
A Review of Carbohydrate Supplementation Approaches and Strategies for Optimizing Performance in Elite Long-Distance Endurance. Nutrients, 2025.
A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise. PLOS ONE, 2014.
Podlogar, T., Wallis, G. A. Dietary Carbohydrate and the Endurance Athlete: Contemporary Perspectives. GSSI Sports Science Exchange, 231, 2022.
Spriet, L. L. Caffeine and Exercise Performance: An Update. GSSI Sports Science Exchange, 203, 2020.
