Once you start training for a long race, be it 10k, 1/2 or full marathon, or 50k.  You may start looking into longer races.  You may do like I did and try to find/read anything that might help make it a little easier or make me faster than molasses finally.  For me, the people who can finish a 50 – 100 mile race are definitely super human.  I look at how they train and what they eat before, during and after the race.  This is an interesting article about the Western States 100 running nutrition.  It is a good guide to how to adjust your nutrition depending on the conditions.  It is always a balancing act.  As a larger runner, you will also burn more calories than your smaller counterparts!