Not if you need high-quality carbohydrates that will work most effectively for your long-term running. Here’s the main point: empty calories are your enemy, and not are a healthy way to prepare for a marathon. These energy gels have about 100 calories and give you the carbs you need without anything that you don’t need.
Having said that, we are talking about the gels being a way to access 100% energy-rich food which digests very quickly into the body and gives you a boost of stamina and energy. If you were to consult a dietician it is certain that they could advise a diet which you could follow in the days building up to a race and this diet combined with training would be another way to improve your endurance and stamina but though dieticians are excellent you need to keep in mind that they will charge a fee.
If you are very regularly competing in physically demanding races at a professional level diet is a very important factor. If you occasionally enter a marathon run then the energy gels are a perfect alternative to get needed energy at exactly the time you choose to need it.