Looking for evidence that personal hygiene precautions prevent traveler's diarrhea

In the 50 years during which traveler's diarrhea has been studied, it has always been assumed that personal hygiene precautions can prevent or reduce the likelihood of developing traveler's diarrhea. However, 7 of 8 studies that specifically addressed this issue showed no correlation between the types of food selected and the risk of acquiring traveler's diarrhea. The eighth study showed a correlation between a few dietary mistakes and a decreased risk of acquiring traveler's diarrhea. A further increase in the number of dietary mistakes, however, did not continue to increase the risk of acquiring traveler's diarrhea. Personal hygiene precautions, when performed under the direct supervision of an expatriate operating his or her own kitchen, can prevent traveler's diarrhea, but poor restaurant hygiene in most developing countries continues to create an insurmountable risk of acquiring traveler's diarrhea.