An estimate of the proportion of colo-rectal and stomach cancers which might be prevented by certain changes in dietary habits.

The colo-rectum and stomach are the 2 sites for which the role of diet in the etiology of cancer is most heavily implicated. Quantitative estimates as to the proportion of cancer deaths attributable to diet vary considerably. This may be partially due to the application of the concept of population attributable risk which has proved a useful yardstick in estimating the public health impact of completely removing an exposure factor under study. This simple concept may well serve in occupational epidemiology, but with more and more risk factors found on a metric scale, or at least characterized on an ordinal scale, extensions should be considered. In this report, a preventable proportion is defined as the excess risk which would be removed if the population exposure distribution were to change ina favorable direction. A simple way of modelling such changes is proposed. This new measure is illustrated with data from 6 case-control studies on colo-rectal or stomach cancer. The results indicate that the proportion of these cancers which may be prevented assuming arbitrary shifts of a single risk factor towards the next lower risk category if populations were to change their dietary habits is in the order of magnitude of 15% to 20%. This figure is much lower, but not necessarily in contradiction to the figures considered for the proportion of cancers attributable to diet.