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While some retrospective studies have reported that certain dietary habits may affect rectal cancer, the types of dietary habits involved are limited. We employed a classical 2-sample Mendelian randomization approach to investigate the causal relationship between dietary habits and rectal cancer. Rigorous instrumental variable selection included P-value filtering, linkage disequilibrium assessment, and sensitivity analyses utilizing methods like Steiger filtering and Mendelian Randomization Pleiotropy RESidual Sum and Outlier to ensure robust inference. Utilizing Mendelian randomization, we assessed the influence of dietary habits on rectal cancer using data from 706 single nucleotide polymorphisms derived from the UK Biobank. Our analysis, incorporating rigorous instrumental variable (IV) selection and sensitivity checks, revealed significant associations for 5 dietary habits with rectal cancer. Notably, herbal tea intake (raw P = .007; odds ratio = 0.998; 95% confidence interval (CI) 0.997-0.999), average weekly beer plus cider intake (raw P = .038; OR = 0.867; 95% CI: 0.757-0.992), pancake intake (raw P = .040; OR = 0.753; 95% CI: 0.574-0.987), and salad/raw vegetable intake (raw P = .049; OR = 0.809; 95% CI: 0.6554-0.9995) were found to have a protective effect against rectal cancer. Conversely, we found the average weekly spirits intake (raw P = .041; OR = 1.261; 95% CI: 1.010-1.575) to be a potential risk factor for rectal cancer. Our findings suggest that several genetically proxied dietary traits may be associated with rectal cancer risk. These findings should be interpreted cautiously and require validation in independent and ethnically diverse populations before informing dietary recommendations.