- Strict Vegetarians will be excluded from the study; it was found that consuming one portion per day of fruit or vegetables resulted in a significant decrease in oral cancer incidence; in those persons consuming multiple portions each day, there was a 50% reduction in risk; we assume that strict vegetarians will consume multiple portions each day of foods with chemopreventive activity and therefore inclusion of these individuals would have a negative impact on the study; there are several reports in the literature that herbal or multivitamin/mineral supplements have no effect on oral cancer incidence