Posted: 09/01/2015 at 19:13
you'll get different advice from different people as we are all ... different.
Listen to the advice, but experiment on your long runs to find what works for you, and most importantly what doesn't upset your stomach. Running a marathon tests your gastric system along with the rest of your body.
Personally, two mistakes I've made that may be relevant to you:
(1) London has water stations every mile, so be disciplined and work out prior to the race how frequently you'll take a drink and resist the temptation to drink too often, as its easy to take on too much water.
(2) On my last marathon, I took my own gels but then took some isotonic drinks from the stations. This was a mistake as the combination was too much for my stomach, causing stomach cramps etc. I'd trained with gels and plain water, and should have stuck to that.