Cesium has a biological half life of one to four months. Removing yourself from the source of exposure, or diversifying your source of food to include produce from out of the affected area can almost completely eliminate internal contamination.
Certainly bio-accumulation is going to be a concern, especially after what we saw in Chernobyl. But unlike the Soviet disaster, most people in Japan don't acquire their food stuffs solely from local farms, and the contamination outside of Fukushima prefecture is almost nothing.
I live in one of the most contaminated areas outside of Fukushima, and the majority of food samples are testing free of cesium. Here are the testing results for August 2012; nothing detected. Here are the testing results for August of last year; only blueberries show cesium contamination at 44.6 bq/kg. Landlocked, fresh-water fish in my area have shown the most contamination, and as a result, they have been prohibited from consumption. Also, my family can avoid produce from Fukushima and Ibaraki prefecture as we live in a first-world nation with access to lots of alternatives.
The people living to the N/NW of Fukushima Daiichi (like in Iitatemura) got screwed the most because of government incompetence and lying. Most of those areas with the highest levels of contamination, including the more dangerous alpha emitters, are now in the exclusion zone, which means that farming is prohibited there. As for actual urine tests, the most cesium tested in a child was 17.5 becquerels per liter with the average being 2.2: Urine Tests These are levels are similar to when nuclear testing was being performed in the 60s.
This was a disaster of epic proportions, but we dodged a huge bullet. Most of the massive amount of radiation was blown out to sea, and even in areas like mine where contamination is high, it's now on par with cities like Hong Kong. In fact, the hospital by my house did a glass badge test for children in the area to test for yearly exposure levels, and not one child tested over an additional 1mSv/year.