Lectin poisoning occurred in Japan in 2006 after a TV broadcast that introduced a new diet of eating staple foods with powdered toasted white kidney beans, seeds of Phaseolus vulgaris. Although the method is based on the action of a heat-stable α-amylase inhibitor in the beans, phaseolamin, more than 1,000 viewers who tried the method suffered from acute intestinal symptoms and 100 people were hospitalized. Lectins in the white kidney beans were suspected to be the cause of the trouble. We were asked to investigate the lectin activity remaining in the beans after the heat treatment recommended on the TV program. The test suggested that the heat treatment was insufficient to inactivate the lectin activity, which, combined with our ignorance of carbohydrate signaling in the intestine, was the cause of the problem.