Energy gels explained: fueling strategies for runners and how to use them effectively

Original publisher: Nature. This article explains how energy gels fuel endurance running, how they work, the evidence around performance benefits, and practical tips for training and racing.

• Gels deliver fast, concentrated carbohydrates mid-race, but effects vary and GI distress is possible.
• Carbohydrate content and osmolality vary across products; start with small doses and test in training.
• A glucose and fructose blend can improve carbohydrate delivery during intense efforts.
• Gels may offer similar benefits to drinks or foods when calories are matched; hydration with water remains essential.
• Shorter runs (60 minutes) may not require gels; plan fueling around endurance duration and training tolerance.

Overview

Energy gels have become a staple for many runners, offering a convenient, mid-race source of carbohydrates. This article synthesizes what is known about how gels work, their potential benefits for endurance performance, and their drawbacks, including cost and gastrointestinal (GI) discomfort. While gels can provide precise dosing, scientists remain divided on how consistently they boost performance, and individual tolerance varies. The piece also emphasizes the value of testing any fueling strategy in training rather than on race day. The original publisher is Nature.

"Gels can be a convenient way to fuel mid-run, but GI distress is a commonly reported issue" - Nature

How gels fuel endurance

During exercise, glycogen stores in the muscle and liver supply energy, but these stores are finite and can be depleted after roughly 90 minutes of sustained activity. Energy gels provide a fast, concentrated source of carbohydrates that can be ingested without breaking stride, in contrast to some whole foods that may be harder to digest during running. The gels discussed typically contain maltodextrin and fructose blends, designed to supply glucose to muscles efficiently and to tap into multiple carbohydrate absorption pathways, potentially widening the available carbohydrate supply during long efforts.

"A mix of glucose and fructose appears to be most useful when intensity is high" - Nature

Product variability and evidence

Research indicates substantial variation among gel products in serving size, carbohydrate content, free sugars, and osmolality, which can influence tolerance and energy delivery. Some classic studies suggested gels and drinks deliver carbohydrates to muscles at similar rates, a point later supported by newer data. Taken together, these findings imply that the unique advantage of gels is not universally energy delivery but the convenience and precision they offer, especially when a race demands quick, mid-activity fueling.

"There’s a lot of variation between available products, especially osmolality, which has implications for how and when you should use gels" - Nature

How to use gels effectively

Practical guidance centers on race duration and pacing. For runs under 60 minutes, gels are often unnecessary. For 60–90 minutes or more, consuming around 30–60 g of carbohydrates per hour helps maintain energy before fatigue. Very long races may require 60–90 g/hour, with glucose-fructose mixtures supporting energy delivery during high-intensity segments. The consensus across studies is to practice with gels in training to gauge tolerance, taste preference, and whether they provide measurable performance benefits. Staying hydrated with water alongside gels is frequently advised to mitigate GI discomfort caused by concentrated sugars.

"The most important thing is to test gels while training. Don’t use them for the first time on race day" - Nature

Downsides, alternatives, and practical tips

Gels are not universally better than alternatives such as sports drinks, chews, or simple foods. They can be expensive, palatability varies, and GI distress remains a common challenge for some runners, especially when hydration is inadequate. Hydrogel-based products attempt to modulate water transport in the gut, but evidence of superior performance or reduced GI symptoms is not consistent when calories are matched. For those who experience persistent GI issues, brands and formulations can be swapped in training to find tolerable options, or athletes may rely on bread, fruit, dates, or rice cakes, with careful practice to understand how these fuels affect performance at different intensities and durations.

"Gels may not offer any additional benefits over other products, such as sports drinks, when calories are matched" - Nature

Key takeaways for athletes

• Gels are a convenient, precisely dosed carb source for mid-race fueling, with clear utility for longer events, provided tolerance is good.
• Expect variability across products; test with the water you plan to drink and in training sessions that mimic race conditions.
• While glucose-fructose blends are often advantageous during intense effort, hydration strategy remains essential to minimize GI issues.
• If gels bother you, there are viable alternatives that can meet energy needs during endurance events, but they may require more planning and practice.

The article consolidates current evidence and emphasizes practical testing and personalization for endurance runners seeking to optimize fueling, while acknowledging that gels are one tool among many in a balanced nutrition strategy for performance and health.