Refuelling in training

I am wondering whether it is necessarily a good idea to re-fuel during longer training runs. I have in the past, mainly to get used to actually using them, so I know which gels suit me. However, now I have a feeling that I might be better not re-fuelling in training, to assist in fat burning, and leave the gels until the actual day of the race. Any thoughts?

www.mcmillanrunning.com talks about that very idea.

I think it's a trickier question than it sounds. I know McMillan advocates a ''running on empty'' approach to promote better fat burning but I personally get a bit scared of trying it out.  If you 'bonk' during a long run, apart from the fact that it's an uncomfortable experience, the loss of energy can't help with your training in general.  So I understand the theory but I think it's a balancing act between promoting fat burning and at least being able to successfully complete the long runs which will promote the necessary endurance fitness.

I tend to take the approach of taking on enough fuel to get through the runs without wilting.  That generally means no more than 500ml Lucozade Sport for 20 - 23 miles, although depending on time on feet others might need more.  Anything up to 2 hours I'll just make sure I'm topped up and well hydrated before I go out, or possibly drink water along the way if it's warm.  I generally save the gels for the dress-rehearsal runs/preparatory 20 mile race a few weeks before.