I read a previous post in which a man suggested that his hair was better outside of the United States. I too have experienced a similar experience. In the beginning of 2007 I took a trip to Israel and stayed there for a month. You mentioned diet as being a possible cause. I ate alot of olives, salads, soups, eggs, and food made from scratch on a kibbutz. I also swam in the dead sea at least twice a week. I noticed that my hair over that month got dramatically thicker. However, when I returned to the U.S., I experienced a massive shed, and over a period of three months, I was back to baseline, prior to the trip. I have only minor thinning in behind my hairline.
Dead sea causing dead hair?! All joking aside, I do not have a good explanation for you on your hair loss after traveling abroad. Diet could be a possible cause. You can also consider stress involved in travel, as well as a component of genetic hair loss for an explanation of more hair loss with traveling in those that have it.