This might be long discussion to explain, and I am not sure there is a Zone answer, either.
Years ago, I used to travel to California about once every 2-4 months for a week at a time.
(Previous Company, over 12 years ago.)
At the time, I noticed that after being out there 1 day, I would get some intestinal queasiness.
It took a couple of trips, talking to "knowledgeable" folks, and doing a bit of research to realize that each area has its own unique bacteria, and one builds immunity to the effects of their own local bacteria, primarily in the region's water supply.
So, I started carrying bottled water with me, and refilling the water bottles from the filtered water at the hotel or office I was working out of.
And gradually acclimating my body to the local water (bacteria), by ingesting local water in slowly increasing amounts each day.
And all has worked well, until recently.
You see Dr. Sears came out with the Zone Foods. And only upon return from this last trip, yesterday, was I able to put it together.
I used the Zone Foods for a trip to Berlin, Germany, Spring 2011 - no problem, but there I ate more local food and drank more local water.
We were not on per diem, but per meal reimbursement, so it made sense to eat locally.
However, recently our company switched to a straight per diem meal replacement policy.
Now I was able to purchase in advance just prior to my trip, the (now defunct) expensive Zone Foods, freeze, and then pack in my luggage just before leaving for the airport. I had a trip to Western Canada fall 2011, and most recently, returned from Singapore Saturday 11:30 PM.
After each of these two trips, I felt the same effects I used when I traveled to California, before I started using bottled water.
But this time, it was back in my home town.
On this last trip, it hit me on Sunday late afternoon, after ingesting a lot of our local hwater, to re-hydrate after traveling for 31 hours (flight time of 24 hours flying). So I started thinking about it Sunday evening, and the following hit me.
Because I was using ALL Zone Foods, and drinking ALL bottled water, these last two trips, especially because I was in a foreign country, that to some degree, my theory is that my system became some what less biologically active with my local bacteria/immunity.
In some way, and not knowing the complete science of it, and for lack of complete understanding, I'll use a term to convey my theory, that I in some way sterilized my self, from the local bacteria!
So, there appears to be a down-side, I did no consider from using exclusively ZoneFast Foods while traveling, especially to other countries.
They are no longer available; however, should a new version be reincarnated, as I hear there might be this Fall - this is something to keep in mind for future travels.
Yes, my theory is only based on observation; and only of one person, and only with two events. Not necessarily a scientific basis.
But, I believe there is some credibility, even if I do not know all of the biological processes and components involved.
Not saying there is anything wrong with using the Zone Foods, of any kind, existing or defunct versions - just learned to not totally rely on them, and to pay even closer attention. Who would have thought that eating the Hormonally controlled foods for a perfectly balanced diet, while traveling - would cause a reverse locality bacteria intestinal problem.
Fortunately, I am very healthy, take no medication (never have), eat right, exercise regularly - so it only lasted from late afternoon Sunday, to early morning Monday. Not bad for a (soon to be) double-nickel aged guy.