The high prevalence of varicose veins in Western countries contrasts with their relative rarity in traditionally living communities in the Third World. Evidence is presented in support of the hypothesis that a major causative factor is the transmission of raised intra-abdominal pressures to the veins of the legs. One important cause of these pressures is the abdominal straining necessitated to evacuate small firm stools, which in turn are the result of fiber-depleted diets.