Energy gels keep you fueled during the hardest sessions, the quick workouts, and the longest efforts, but timing and type matter. This guide explains how they work, when to take them, and which ones to try.
Your body stores roughly 500 grams of carbohydrates, which translates to about 2,000 calories. That sounds like a lot until you consider what happens during a long run or ride. At moderate to high intensity, those reserves last 90 to 120 minutes. After that point, you enter a state endurance athletes know all too well: the bonk.
Your legs stop cooperating, your brain turns foggy, and the finish line feels impossibly far. Energy gels are designed to prevent this, and knowing how to use them correctly can mean the difference between a strong finish and a painful shuffle to the end.
This guide explains how to use energy gels for endurance activities. We cover:
The science behind glycogen depletion
How gels work when consumed
Proper timing and dosing for different race distances
Gastrointestinal problems that can arise
Strategies for training your gut
By the end, you will have a practical framework for incorporating gels into your training and racing.
How Your Body Fuels Endurance Exercise
The human body relies on two primary fuel sources during physical activity: carbohydrates and fat. Fat stores are abundant in most people, but fats break down slowly into usable energy. Carbohydrates can be processed much faster, and the harder you work, the more your body draws from carbohydrate stores rather than fat.
Carbohydrates are stored as glycogen in two central locations: the liver and the muscles. The liver stores about 100 grams of glycogen, while muscles store between 350 and 700 grams, depending on factors such as training status, diet, muscle fiber composition, sex, and body weight. Muscle glycogen powers the contractions that keep you moving. Liver glycogen maintains blood glucose levels and, importantly, fuels your brain.
Here is where things get interesting. During exercise lasting 90 minutes or longer at moderate to high intensity, liver glycogen becomes substantially depleted when you do not consume additional carbohydrates. High-intensity efforts like sprinting or heavy lifting burn glycogen at 4 to 5 mmol/kg/min, which can deplete your glycogen stores within 90 to 120 minutes.
The phenomenon known as hitting the wall, or bonking, occurs when glycogen stores are critically low. This is not simply extreme tiredness. Bonking can cause symptoms such as dizziness, confusion, shakiness, and altered mental status. Your brain runs exclusively on glucose from liver glycogen, so as muscles absorb more blood glucose during extended exercise, less glucose reaches the brain. The result is that hazy, disconnected feeling that makes you question why you ever signed up for this race.
What Energy Gels Are and How They Work
Energy gels are concentrated carbohydrate supplements in liquid or semi-liquid form that athletes consume during exercise. Most gels contain 20 to 30 grams of rapidly digestible carbohydrates, with some products providing up to 40 grams per serving. A typical gel weighs around 30 grams, delivers about 20 grams of carbohydrates, and provides roughly 100 calories.
The main carbohydrate in many gels is maltodextrin, which breaks down quickly and delivers glucose to your bloodstream. Many gels also contain simple sugars such as glucose and fructose. Studies show that combining glucose and fructose in a 2:1 ratio can increase carbohydrate uptake compared to glucose alone because your body uses different transporters for each sugar.
Glucose raises blood sugar quickly, while fructose raises it more gradually. Combining these sugars during exercise allows for greater carbohydrate absorption per hour.
When you consume a gel, the carbohydrates break down into glucose that enters your bloodstream. This glucose is either used immediately for fuel or stored as glycogen. However, gels do not provide a direct one-to-one replacement for depleted muscle glycogen. The carbohydrates must first be digested, pass through the intestinal wall, and then be absorbed by the muscles. This process takes time and is not perfectly efficient.
Some people notice a mental boost after taking a gel, likely due to increased blood glucose.
How Quickly Energy Gels Take Effect
Energy gels are designed for fast absorption. Most people feel the effects within 5 to 15 minutes, though this varies by individual and gel formulation.
Some athletes notice a boost within 3 minutes, while others may wait up to 15 minutes. Isotonic gels often absorb faster than thicker or more concentrated gels. Expect to feel the effects within 5 to 10 minutes after consumption.
The absorption rate varies with factors such as blood flow to the digestive system. Taking gels earlier in your activity gives your body time to process the carbohydrates before you need them.
Timing Your First Gel and Subsequent Intake
A common mistake is waiting too long to take your first gel. Take your first gel about 30 minutes into your activity if it will last 60 to 90 minutes or longer.
After your first gel, continue taking additional gels every 20 to 45 minutes, depending on your needs and race duration. Some people use one gel every 45 to 60 minutes, while others prefer every 30 to 40 minutes for longer events.
The American College of Sports Medicine recommends 30 to 60 grams of carbohydrates per hour during exercise. For events longer than 2.5 hours, intake may increase to 60-90 g/hour if tolerated.
Start fueling before your energy stores dip too low. Take your first gel around the 30- to 45-minute mark, then follow up at regular intervals to help keep your energy steady.
Fueling by Race Distance
Fueling strategies vary by race distance. See below for gel requirements by event duration.
Runs Under 90 Minutes
For runs under 90 minutes, energy gels are generally not needed. Your body’s existing carbohydrate stores usually support activities lasting less than an hour.
Half Marathon
Most runners consume 2 to 4 gels during a half-marathon, depending on their finish time. If your race will take longer than 90 minutes, a range of 1 to 3 gels is typical. Some runners finishing between 1 hour 30 minutes and 2 hours may use gels, depending on their preference and training.
Take your first gel around the 45 to 50-minute mark and another as you approach 90 minutes. Space gels 30 to 45 minutes apart.
Marathon
Most marathon runners deplete their muscle glycogen before finishing. At marathon pace, glycogen typically lasts about 2 hours. Most runners need external fuel to complete the distance.
Most marathon runners use 3 to 5 gels, taken every 30-45 minutes starting around the 30-minute mark. For a 4-hour marathon, 4 to 8 gels are commonly used. Taking more than this may cause stomach issues for some people.
Ultra Endurance Events
For events lasting more than 3 hours, 60 to 90 grams of carbohydrate per hour is appropriate for most athletes. Some research supports 100 to 120 grams per hour with prior gut training, but this may cause stomach issues without preparation.
Quick Reference: Gel Intake by Event Duration
| Event Duration | Gels Needed | Timing | Carbohydrates Per Hour |
|---|---|---|---|
| Under 60 minutes | 0-1 | Not neccessary, but 1 at beginning is okay | The body stores sufficient |
| 60-90 minutes | 1-2 | Around 30 minutes in, then after 30min more | Up to 60g |
| 1.5-2 hours | 2-3 | First at 30 min, then every 30 min | 60-90g |
| 2-3 hours | 3-5 | First at 30 min, then every 30-45 min | 60-90g |
| 3-5 hours | 4-8 | First at 30 min, then every 30-40 min | 60-90g |
| 5+ hours | 8+ | Every 20-40 min | 60-120g (trained gut) |
Hydration and Energy Gel Absorption
Take gels with water to support absorption and reduce the risk of stomach problems. Energy gels are concentrated products and require hydration.
A standard guideline is 250 mL of water per 20 to 25 g of carbohydrate. Drinking 200 to 300 mL of water after taking a gel facilitates absorption.
Isotonic gels are formulated to match your body’s fluid balance and may be taken without extra water. For standard gels, drink water with or after the gel.
Avoid combining gels with sports drinks. Use water to reduce the risk of stomach upset.
Gastrointestinal Side Effects
Stomach problems are common with energy gels. Symptoms include bloating, nausea, cramps, gas, and diarrhea.
Why Gels Cause Stomach Issues
The high sugar and carbohydrate content of gels can be difficult to digest, especially during exercise. Several factors contribute to gastrointestinal distress.
Consuming gels without sufficient water may lead to digestive issues and dehydration. Reduced blood flow to the gut during exercise slows carbohydrate absorption, and unabsorbed carbohydrates can cause gas, bloating, and diarrhea.
Running increases gut motility, which can trigger bowel movements. Reduced blood flow during exercise may also cause nausea, vomiting, pain, and diarrhea.
Certain ingredients can cause more problems. Fructose and high caffeine content may cause gas or gastrointestinal upset in some people. Unabsorbed carbohydrates may ferment, leading to bloating, cramping, and diarrhea during exercise.
Reducing Stomach Problems
Several strategies can help minimize stomach problems:
Water: Take gels with 200 to 300 mL of water per gel.
Limit intake: Do not exceed two gels per hour; your body absorbs about 60 to 90 grams of carbohydrates each hour.
Timing: Start fueling early. Taking a gel late in a race is more likely to cause problems if your stomach is already under stress.
Familiar brands: Train with the gels you plan to use on race day. If your event offers a specific brand at aid stations, use that product in training.
Training Your Gut
Your digestive system adapts with practice. Athletes who regularly use gels in training develop better tolerance for race day.
Train your gut by using gels at the same intervals and intensities you plan to use during your event. For example, practice taking a gel every 30 minutes during long runs if that is your goal for race day.
Practice your competition-fueling plan to minimize the risk of stomach discomfort. Increasing intake above 60 grams per hour may require adaptation during training.
If you plan to consume 90- 120 grams of carbohydrates per hour during ultra-endurance events, train for this intake in advance. Increasing your dose suddenly on race day may cause stomach problems.
Caffeine in Energy Gels
Many energy gels contain caffeine, which may delay fatigue and increase alertness. Research indicates that caffeine consumed before or during exercise can enhance performance.
Caffeine content varies by product. Some gels contain 20 milligrams, while others have up to 100 milligrams.
Caffeine can accelerate carbohydrate absorption. Some athletes use caffeinated gels late in a race for a boost, while those who are sensitive may prefer caffeine-free options.
Timing Before Exercise Starts
Taking a gel 1 to 2 hours before exercise may cause a drop in blood sugar just as the race begins, leaving you feeling tired. Avoid taking a gel within 15 minutes of starting your event unless you are already exercising.
Post-Exercise Recovery and Glycogen Restoration
Restoring muscle glycogen after intense exercise takes time. Complete replenishment requires at least 48 hours. The first 30 to 40 minutes after exercise is a window of rapid glycogen synthesis.
During this phase, glycogen synthesis is faster. Consuming 60 to 90 grams of carbohydrates within 15 to 30 minutes after exercise maximizes muscle glycogen storage.
For athletes training multiple times per day or on consecutive days, post-workout nutrition is as important as fueling during exercise. It takes at least 20 hours to restore muscle glycogen after intense workouts.
Common Mistakes to Avoid
Common mistakes with energy gels include:
Timing: Don’t wait too long to take the first gel. Start at ~30 minutes into your activity.
Limit intake: Taking too many gels at once. Don’t exceed 60 to 90 grams of carbohydrates in a short time frame if you aren't gut-trained.
Hydration: Skipping water. Always take gels with water for proper digestion and absorption.
Familiar brands: Trying new products on race day. Train with the gels you plan to use.
Gut training: Don’t ignore gut training. Practice your fueling strategy during training.
Pre-exercise timing: Taking gels too early before starting. Avoid gels 30-60 mins before exercise.
Energy Gels FAQs
How many grams of carbohydrates are in a typical energy gel?
Most energy gels contain 20 to 30 grams of carbohydrates, though some products provide up to 40 grams per serving.
How long do energy gels take to work?
Most athletes feel the effects within 5 to 15 minutes after consumption. Some may notice a boost within 3 minutes, while others may wait up to 15 minutes, depending on individual physiology and gel formulation.
Do I need energy gels for a 10K race?
For runs under 60 minutes, energy gels are generally not vital. Your body stores enough glycogen to fuel approximately 90 minutes of exercise, but taking one at the start can support blood sugar levels.
How much water should I drink with an energy gel?
Aim for 200 to 300 mL of water per gel. A general guideline is that approximately 20-25 grams of carbohydrates requires 250 ml of water for processing.
Why do energy gels give me stomach problems?
The concentrated sugars can be difficult to digest, especially when blood flow is diverted from your digestive system to working muscles. Insufficient water intake, excessive gel consumption, fructose content, and lack of gut training all contribute to gastrointestinal distress.
How do I train my gut to handle energy gels?
Practice your fueling strategy during training sessions at intensities and intervals similar to those encountered in races. Over time, your intestinal absorptive capacity will increase, and tolerance will improve.
Can I take energy gels before exercise starts?
Taking a gel within 15 minutes of starting is fine. Consuming a gel 30-60+ before exercise can trigger an insulin response that lowers blood sugar and leaves you feeling tired at the start.
How long do energy gels last before expiring?
Energy gels have expiration dates, typically 12 to 24 months from the date of production. For example, GU Energy Gels and Honey Stinger have an 18-month shelf life. Spring Energy lists a 6-month Best-By date.
Best-By dates indicate the period during which optimal taste and performance are expected. In the United States, these dates are not legally required except for infant formula. Manufacturers provide them as guidance.
Some gels remain safe for up to 6 months after the Best By date if stored properly. Best By dates indicate flavor, not safety cutoffs.
Store gels in a cool, dry place away from extreme temperatures. Sugars and salt help retain texture, but liquid gels have a shorter shelf life than dry products.
What is the maximum amount of carbohydrates I should consume per hour?
Your body absorbs more than previously thought. Most athletes should aim for a benchmark of 60 g per hour, training up to 90 g for longer events. Athletes who have trained their gut can sometimes tolerate 100 to 120 grams per hour during ultra-endurance events, but exceeding 90 grams without prior gut training often leads to gastrointestinal issues.
Should I use caffeinated or caffeine-free gels?
Caffeinated gels can help delay fatigue and improve alertness, and caffeine also accelerates carbohydrate absorption. However, athletes sensitive to caffeine or prone to stomach issues may prefer caffeine-free options.
Putting It All Together
Energy gels are a proven tool for endurance athletes, but their effectiveness depends entirely on how you use them. The science is straightforward. The body stores a finite amount of glycogen, which is depleted during prolonged exercise, and gels provide rapidly absorbed carbohydrates to maintain blood glucose and delay fatigue.
The practical application requires attention to timing, quantity, hydration, and gut training. Start your first gel before depletion becomes a problem, typically around 30 minutes into exercise lasting over an hour. Take subsequent gels every 30 minutes. Drink water with each gel. Practice your exact fueling strategy during training so your digestive system knows what to expect on race day.
Your individual needs will vary based on intensity, duration, fitness level, and how your body responds to different products. Experimentation during training is essential. By the time you reach your goal race, you should know exactly which gels work for you, when to take them, and how much water you need. Getting this right will not guarantee a personal best, but getting it wrong can guarantee a miserable last few miles.
