Endurance athletes consume highly concentrated carbohydrate solutions because it maintains blood glucose levels and spares limited accessible energy sources. There are many “energy gel” sports nutrition products to choose from.
They can be costly, anywhere from $1 per 25g of carbohydrates to as much as $3.5 per 25g for high-end solutions. If you’re running a 4:00 marathon, that means spending $8-$28 for 60g per hour, or twice as much to use a higher dosage. Once you factor in the need to practice with them before a race, you might spend about $50-$150 per marathon training block on gels.
Fortunately, it’s easy to make passable gels at home. The basic idea is to use honey and maltodextrin to get a 3:1 glucose to fructose ratio, then add water to reach a manageable concentration.
DIY means you can easily add caffeine and salt, or substitute a carb source, all with the flexibility to use the containers of your choice. I am partial to these 100ml flip-cap plastic pouches which fit in most shorts’ gel pockets. For workouts, I dump the ingredients in a bottle, energy drink style.
- Add honey (or pure fructose) to water and mix until dissolved.
- Add maltodextrin and mix until dissolved.
Keeps for atleast 2-3 days in a refrigerator.
How many carbs per hour?
The recommendation for events longer than an hour is 60g per hour, and there’s evidence of performance and recovery benefits for using as much as 120g of carbohydrate an hour (in elite endurance athletes). Tolerance varies between individuals and is trainable.
Glucose and fructose use separate metabolic pathways. The recipe defaults to a low amount of fructose compared to common recommendations of 2:1 or 1:1 ratios because using honey keeps the flavor tolerable, and because fructose is largely a moot point until you’re able to saturate the glucose pathway. If you want to go lower than 1.25:1 you’ll need to swap honey, and it’s tag-along 30% glucose content, for pure fructose to keep the osmolality manageable.
Osmolality and isotonicity
Absorption is best if the solution is isotonic, meaning it has osmotic concentration (units mOsm/L, milliosmole per liter) matching that of bodily fluids. If the solution is too concentrated, it’ll cause GI stress as fluids are pulled in. If it’s too dilute, it’ll pass quickly before full absorption. The only way to change osmolality while holding carbohydrate mass constant is to use fewer particles (e.g. use heavier carbohydrates, like maltodextrin, which are still quickly metabolized) or add more water. Given the typical estimate of blood plasma osmolality at 280 mOsm/L, the default 4300 mOsm/L for this recipe is high (albeit similar to that of most commercial products). Making the solution isotonic will usually involve adding so much fluid as to make it impractical (and doesn’t align with fluid consumption of high-performing athletes either).
Maltodextrin is a large molecule consisting of chains of glucose and is created by chemically processing starch. Its properties are somewhere between that of starch and pure sugar; less sweet and crystallization-prone than sugar, but also less viscous in solution than a starch. It is quickly broken down into glucose inside the body, and is typically easier to tolerate in large quantities. All of this is why it’s the primary carb source in commercial gels.
Unfortunately, the length of the glucose chain is variable depending on the chemical process and starches used. Anything between 2 and 20 glucose groups (degree of polymerization) are sold alike. Longer chains are preferable as they’ll result in a lower osmolality. You can contact the manufacturer to get the number, but generally longer chain versions will take longer to dissolve in water and will be barely sweet. The calculator assumes a degree of polymerization of 10 (I was quoted 10-12 by a representative of the company I use).
The recommendation is 3-6mg caffeine per kilogram body mass, spread through the window starting an hour before the event to an hour before completion. Caffeine powder is dangerous and easily mishandled. Save yourself the trouble; buy capsules and dump the contents in as needed.
You can also use this gel/drink recipe in the lead up to a big event for an easy-to-tolerate carb load. See this helpful calculator for an idea of how many carbs and when to eat them.
- Honey: $6/lb, 1 ⅓¢/g, 1lb grocery store container.
- Maltodextrin: $6/lb, 1 ⅓¢/g. 4lb (1 gallon) container.
- Fructose: $8/lb, 2¢/g. 3lb bag.
- Caffeine: 5¢/100mg, 250 capsule container