Bonking is when the body runs out of necessary sugar energy and is forced to turn to other less efficient sources of energy. Sugar is the only thing the body can use for energy, so when it runs out, it’s forced to convert protein (muscle) into sugar.

This conversion process has serious side effects. When marathoners reach this point they are said to have “bonked.” The human body can store enough sugar energy to sustain a typical marathoner for between 45 minutes to an hour. After that you have a choice. You can try and “bonk” for the rest of the marathon, or you can use energy gels or energy drinks.

Energy gels are designed to be digested almost immediately and provide the body with sugar that can be used for energy. These energy boosts usually last for 15 to 30 minutes. Marathoners can avoid the “bonk” by taking an energy gel after the first 45 minutes and then every 20 to 30 minutes after that.

The body can only absorb around 400 calories per hour. Most gels contain anywhere from 90 to 150 calories.

So generally, 3-4 per hour are enough to maintain good energy levels. If a runner tries to consume more than 400 calories every hour, the runner may become nauseated since the body can’t absorb the sugars and carbohydrates fast enough.

Consuming a sports drink will have the same effect as the energy gels. Sports drinks like Cytomax and HEED contain carbohydrates and sugars just like the gels. Some people find them easier to digest than the gels, and they usually contain a more rounded electrolyte supplement.

Here are some of our top tips for staying hydrated:

  • Using a combination of gels and a sports drink concurrently can cause problems. Typically, runners will avoid using both due to the fact that the body can’t digest the excess sugars and carbohydrates fast enough. It’s recommended to separate the two, meaning use either gels or a sports drink as your energy source, not both.
  • If using just gels, you will more than likely need an alternative source for electrolytes and hydration. Water by itself for hydration is not enough. Gels have some electrolytes, but usually just potassium and sodium. A good electrolyte replacement will have more than that.
  • Sports drinks can be enough for your hydration/electrolytes and energy needs, depending on the person. If you sweat profusely it could be tough to keep yourself hydrated properly and maintain your 200 to 300 calories per hour.

To find what works for you will be a matter of trial and error. Everyone is different so what works for someone else may not work for you.

Good energy gels:

  • PowerBar
  • Hammer
  • GU
  • E Gels
  • Accelerade
  • Cliff Shots
  • Cliff Blocks
  • Carb BOOM

Good sports drinks:

  • Cytomax
  • Gatorade Endurance
  • Cliff Shot
  • Perpetuem by Hammer
  • Sustained Energy by Hammer
  • HEED by Hammer
  • Gleukos
  • EFS by First Endurance
  • PowerBar Endurance
  • Accelerade
  • GU2O
  • Carbo Pro

Good electrolyte products:

  • Endurolytes capsules
  • Thermolyte capsules
  • NUUN tablets
  • Elite drops
  • Ultima Replenisher packets

Words of caution: if you’re not used to eating and drinking while running, you should practice during your training runs. Nobody wants to discover during the marathon that his or her stomach can’t handle this.


Fueling for races over 3 hours long

Long Run and Marathon Nutrition