Nausea during running long distance

Question
Thanks for the advice.  I definitly thought that I would have to test other strategies during long runs but felt that assistance from something like Gu would enhance my performance and thus would have never thought of not taking some kind of a energy substance.  We'll see what happens next weekend.  I would love to hire you, but given my status as a poor college student, I don't think I can afford professional help.  In regards to my times....Last year, I ran a 3:19:30 marathon, and the two years ago, I ran a 3:28 marathon.  In April, I ran three races.  They were a 30:42 8k, 1:22:35 half-marathon, and a 62:30 10-miler.  Since, I have recently done one half-marathon but was unable to compete as I usually do because I had been ill and unable to run for the 12 days before the race.  My goal for the Marathon on 10/22 is under 3:10:59...All I care for is qualifying for Boston.   
-------------------------

Followup To

Question -
I'm looking for some advice to avoid nausea that I often experience when running long distances.  My nausea problem occurs on runs over fifteen miles.  Most commonly, the problem starts when I get to around 18-20 miles.  This phenomena has given me difficulty in at least two marathons and once for a ten mile run.  I have had a couple of hypothesis as to the cause...I once thought over-hydration or lack of food in my stomach(as it seems to empty after running a long duration).  However, my leading suspicion is that the Gu I take causes my nausea.  Do you have any suggestions as to steps that I could take to avoid just missing Boston as a result of nausea again? If you think Gu is the problem, what is it about Gu that I want to avoid?  Is there a particular ingredient that may cause my trouble?  Any guidance would be greatly appreciated so that I can fix my stomach problem before the Chicago Marathon.

Answer -
Hi jim
I'm sure it is the gu.The high sugar content can easily do it.What kinds of times do you run and for the marathon and planing to do in chicago.If you have properly prepared you should be able run the marathon with just water and a few sport drinks.I personally can only handle water in a marathon.Leave the gu behind in a test 20 miler right away.Test,test,test and then you no it works.And second suggestion is hire me.Let me know about your times.

To your success

John

Answer
Good to hear from ya Jim
Those are some really solid times at 8k,1/2,10 mile.With those times you should be able to go sub 3hr.if you back them up with good solid preperation.Let me know how your non gu 20 miler goes this weekend and we can evaluate it together.I do no how important it is to get this right,and time is getting short.Also let me know your traing leading up to the 20 miler since this is also part of the puzzle.

Look forward to your results
this weekend

John