Hi, the research is pretty limited from what I can see.
With more moderate exercise your body will adjust over time to make more use of fats as an energy source but with higher intensity bouts of training, carbs will undoubtedly be beneficial.
It’s worth remembering that the 8 weeks is a temporary measure, to reset your system. After that, while still on a lower carb regime, you will be fuelling your system very differently than when on the 800 cals. You will then have different energy levels and be less likely to hit the wall as soon.
Competitive sports are a very different beast to the moderate exercise most people will undertake. You may benefit from sensible carb loading with low GI, healthy carbs – I wouldn’t use the energy gels! They’re so disgusting anyway so hopefully this shouldn’t be a great hardship!