Comprehensive Assessment of Diet Quality and Risk of Precursors of Early-Onset Colorectal Cancer.

Background The role of poor diet quality in the rising incidence of colorectal cancer (CRC) diagnosed under age 50 has not been explored. Based on molecular features of early-onset CRC, early-onset adenomas are emerging surrogate endpoints. Methods In a prospective cohort study (Nurses' Health Study II), we evaluated two empirical dietary patterns (Western and prudent) and three recommendation-based indexes (Dietary Approaches to Stop Hypertension [DASH], Alternative Mediterranean Diet [AMED], and Alternative Healthy Eating Index [AHEI]-2010) with risk of early-onset adenoma overall and by malignant potential (high-risk: ≥1 cm, tubulovillous/villous histology, high-grade dysplasia, or ≥ 3 adenomas), among 29474 women with ≥1 lower endoscopy before age 50 (1991-2011). Multivariable logistic regressions were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Results We documented 1157 early-onset adenomas with 375 of high-risk. Western diet was positively, whereas prudent diet, DASH, AMED, and AHEI-2010 were inversely associated with risk of early-onset adenoma. The associations were largely confined to high-risk adenomas (OR [95% CI] for the highest versus lowest quintile: Western = 1.67 [1.18 to 2.37]; prudent = 0.69 [0.48 to 0.98]; DASH = 0.65 [0.45 to 0.93]; AMED = 0.55 [0.38 to 0.79]; AHEI-2010 = 0.71 [0.51 to 1.01]; all P trend≤.03), driven by those identified in the distal colon and rectum (all P trend≤.04 except AMED: Ptrend=.14). Conclusion Poor diet quality was associated with an increased risk of early-onset distal and rectal adenomas of high malignant potential. These findings provide preliminary but strong support to the role of diet in early-onset CRC.