Food change due to cooking temperature and unrecognized heat-formed chemical carcinogens may impact on the risk of stomach and colo-rectal cancers. To test this hypothesis a case-control study was performed. A total of 670 cases of stomach and colo-rectal cancers matched with 672 hospital controls for sex and -/+5 years age admitted to three hospitals in Hanoi city in the North Viet Nam from October 2006 to September 2007 were the subjects. Five levels of food change due to cooking temperature were based on food color; white, pale yellow, yellow, dark yellow, and burnt. We asked study subjects to themselves report which of these five colors was their preferable intake before the onset of disease. The present study included; fried fishes-meats-eggs-potato-tofu; grilled foods; roasted foods; sugar, bread, heated wheat, and biscuits. These were cooked at temperatures as high as from 165 to 240 degrees C, based on the literature. Adjusted estimation of odds ratio was conducted controlling for possible confounding factors using STATA 8.0. A high intake of roasted meats, bread and biscuit significantly increased the risk of cancer as much as OR= 1.63, 95%CI= 1.04-2.54; OR= 1.40, 95%CI= 1.03-1.90; OR= 1.60, 95%CI= 1.03-2.46 with probabilities for trend = 0.029, 0.035, and 0.037, respectively. For exposure among controls: 529 (79%) were not exposed at all to roasted meats; 449 (67%) were not exposed at all to bread; and 494 (74%) were not exposed at all to biscuit. Observation of food change due to cooking temperature based on color is practically feasible for detecting associations with risk of developing cancer.