The lessons of life: keynote address to the nutrition and cancer conference.

Some 15 years ago there began to emerge a consensus among epidemiologists that diet might be responsible for 30-60% of cancers in the developed world, in the sense that it should be possible to reduce age-specific incidence rates by this amount by practicable dietary change. Within about 6 years it was also broadly agreed that the principal changes required to bring about this effect were a reduction in the consumption of fat; an increase in the consumption of fruit, green and yellow vegetables, dietary fiber, and some micronutrients; and possibly an improvement in the methods of food preservation. Very small effects, if any, were attributed to food additives and to the pollution of food by trace pesticides, which the public, who accepted much of the consensus advice, have increasingly regarded as important causes of risk. These past conclusions are reviewed in the light of increased knowledge of the etiology of cancer and the trends in its incidence. Contrary to common belief, the trends are broadly encouraging.