Dietary factors and colorectal cancer risk: an ONCODIR systematic review and meta-analysis

Colorectal cancer (CRC) remains a leading cause of cancer morbidity and mortality worldwide. We conducted a systematic review and meta-analysis to evaluate associations between dietary factors and CRC risk comprehensively. Following PRISMA guidance, we searched for observational studies published between 2010 and 2024 (PROSPERO protocol ID: CRD42025642356). We included 123 eligible studies, assessing 35 dietary exposures across 58 syntheses. Pooled estimates were reconstructed from crude, unadjusted data with random-effects models, for both dichotomous and quantitative analyses. Study quality was assessed using the Newcastle–Ottawa Scale, and between-study dispersion was quantified using I2, tau-squared, and 95% prediction intervals. Red meat intake was associated with higher CRC risk in quantitative and dichotomous analyses (quantitative OR 1.38, 95%CI: 1.09–1.75; dichotomous OR 1.58, 95%CI: 1.15–2.16), with similar findings when it was analysed jointly with processed meat (OR 1.52, 95%CI: 1.08–2.15; OR 1.38, 95%CI: 1.20–1.59). Sweets and desserts were associated with higher CRC risk (dichotomous only; OR 1.92, 95% CI: 1.30–2.84). Consistent protective associations were observed for vitamin D (OR 0.76, 95%CI: 0.58–0.99; OR 0.81, 95%CI: 0.75–0.86) and vegetables (OR 0.82, 95%CI: 0.72–0.93; OR 0.79, 95%CI: 0.64–0.98). Several other factors reached statistical significance in at least one model, including calcium, milk, fiber, whole grains, legumes, nuts, fruits, fish, coffee, folate, vitamin E, sodium, and iron. In contrast, cheese, potassium, garlic, chicken, vitamin A, and eggs showed no significant associations. Between-study heterogeneity was high (I 2 above 75% in 42 of the 58 syntheses), and the 95% prediction interval included the null in all 25 syntheses for which it could be calculated, including the 15 whose confidence interval excluded it. Higher intake of red and processed meat was associated with increased CRC risk, whereas plant-based foods and vitamin D were associated with reduced risk. Because these estimates were reconstructed from unadjusted data and every prediction interval included the null, they reflect the average across a heterogeneous literature rather than an effect expected in a new population. They support prevention strategies that prioritize plant-based dietary patterns and limit red and processed meat, and highlight the need for harmonized exposure definitions and higher-quality prospective evidence.