Associations of dietary fat with risk of early neoplasia in the proximal colon in a population-based case-control study. 
Excess dietary fat consumption is strongly associated with the risk of colorectal cancer, but less is known about its role in the earliest stages of carcinogenesis, particularly within the proximal colon.  In the following case-control study, we evaluated the relationship between the intake of dietary fats and the frequency of early proximal neoplasia [aberrant crypt foci (ACF) or polyps], detectable by high-definition colonoscopy with contrast dye-spray.  Average-risk screening individuals underwent a high-definition colonoscopy procedure as part of larger ongoing clinical study of precancerous lesions in the proximal colon.  Dietary fat intake was assessed using the Block Brief Food Frequency Questionnaire, which estimates average dietary intake based on 70 food items.  The diets of individuals with no endoscopically identifiable lesions (n = 36) were compared to those with either ACF or polyps detected in the proximal colon.  In multivariate analysis, high dietary intake of total polyunsaturated fatty acids (PUFAs) and intake of omega-6 and omega-3 fatty acids were positively associated with neoplastic lesions in the proximal colon.  When comparing ACF and polyp groups separately, a positive association was observed for both proximal polyps (OR 2.28; CI 1.16-7.09) and ACF (OR 2.86; CI 1.16-7.09) for total PUFA intake.  Furthermore, the prevalence of proximal ACF was increased with higher intake of omega-6 (OR 3.54; CI 1.32-9.47) and omega-3 fatty acids (OR 2.29; CI 1.02-5.13), although there was no discernible difference in the omega-6/omega-3 ratio.  These results suggest that dietary PUFAs may be positively associated with risk of early neoplasia in the proximal colon.  This study provides further evidence that dietary PUFA composition may play an important role in altering the microenvironment within the human colon.