When you say you get sick after a marathon, do you mean that you come down with a cold or the flu within the week following the marathon, or do you mean you feel sick immediately afterwards on the same day as the marathon? The former is an immunity issue whereas the latter is a hypoglycemia problem (usually).

I just read the June 2003 issue (182) of Peak Performance. It said, "Rapid refuelling [sports drink, etc., immediately after a hard workout] allows for faster replacement of energy in the muscles, thus speeding recovery, and is also good for the immune system."

But the fact of the matter is that a marathon is a jolt to the body and to the immune system, which is not easily overcome by refueling alone. Your best bet is to eat and drink lots immediately after the marathon and get lots of rest and sleep. Recovery exercise should be short and slow. You should avoid hot tubs. If you take a hot shower, interrupt it every 3 minutes with 30 seconds of cold water on your legs. Within a couple days of the marathon, go swimming (at recovery pace). All these things help counteract the shock to the system that you experienced during your marathon.

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Do not take counsel of your fears.--Andrew Jackson

I completed my first marathon two weeks ago, and was sick most of the afternoon with GI distress. I attribute it to a high HR (in the range of my bike LTHR which was much higher than any of my training runs) for the duration of the race which may have caused stomach to shut down. I would be interested to hear an elaboration on why this occurs and how to prevent in the future.