Not all energy gels are the same. They can vary hugely in their consistency, energy content, other ingredients (such as electrolytes and caffeine) and taste. All of these different characteristics mean that they behave very differently in the body and will be absorbed at different rates.

The concentration of a gel is called its tonicity. The higher the tonicity, the more water you need to take with it in order for it to be absorbed optimally. If you don’t take enough water with it, it can sit in your stomach and make you feel uncomfortable and bloated.

The tonicity of a gel can only be measured in a lab with an osmometer and it won’t be marked on the packaging of a gel. The amount of simple sugars will give some indication, however, and more than 5g of simple sugars per gel will indicate the likelihood of a high tonicity.

Isotonic gels offer the best solution as they don’t need any additional water with them in order for them to be absorbed optimally, but still deliver energy quickly. Most standard gels will require 250ml-500ml of water with them in order to make them isotonic. If you take insufficient water with them, water has to be pulled into the gut from the fluid in your cells or blood stream in order to try and dilute it.

Most gels contain between 20-30g of carbohydrate. More than 30g of carbohydrate is quite a lot to take on board at once and will require a lot of water to be taken with it. You should use standard energy gels in an event longer than 90 minutes. Caffeine can be used at any time but is most effective to be saved for the end of a long ride or taken before a short, intensive effort such as a TT or a crit. Electrolyte gels can be an option if you are not using an energy drink containing electrolytes.