Adherence to the Planetary Health and Healthy Plant-Based Diets and risk of colorectal cancer: a prospective analysis of the UK Biobank

Abstract

Higher adherence to the PHD and HPDI was associated with lower colorectal cancer risk in 204,369 UK Biobank participants followed for 11 years. Comparing highest versus lowest adherence, hazard ratios were 0.66 (95% CI: 0.58–0.75) for the PHD and 0.77 (95% CI: 0.68–0.87) for the HPDI. Associations were consistent across tumour subsites. Dietary patterns that emphasise plant-based foods and environmental sustainability may play an important role in colorectal cancer prevention(1–3). The Planetary Health Diet (PHD)1, which promotes high intake of plant foods with limited animal-source and ultra-processed foods, and the Healthy Plant-Based Diet Index (HPDI)(3), which prioritises healthy plant foods over less healthy plant and animal foods, have both been proposed as cancer-preventive dietary patterns(2,3). Higher adherence to these diets may reduce colorectal cancer risk through increased intake of dietary fibre, antioxidants, and anti-inflammatory compounds, alongside lower consumption of red and processed meats, which are linked to carcinogenesis via inflammation, insulin resistance, and alterations in the gut microbiome(4). However, prospective evidence directly comparing the PHD and HPDI in relation to colorectal cancer risk remains limited. We therefore examined the associations between adherence to these dietary patterns and incident colorectal cancer in the UK Biobank. This prospective study included 204,369 participants from the UK Biobank cohort (mean age 56.5 years; 54.3% women). Adherence to the PDH and HPDI was assessed using repeated 24-hour dietary recalls and rescaled from 0 to 1 to ensure comparability. Incident colorectal cancer, including proximal and distal colon cancer, was ascertained through linkage to national cancer registries and hospital admission records. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Models were adjusted for sociodemographic characteristics, lifestyle behaviours, multimorbidity, and body mass index (BMI). During a median follow-up of 11 years (interquartile range: 10.2–11.7), 2,220 participants developed colorectal cancer, 822 proximal and 637 distal colon cancer. Higher adherence to both the PHD and the HPDI was associated with a lower risk of colorectal cancer. Comparing the highest versus lowest quartile of adherence, HRs were 0.66 (95% CI: 0.58–0.75) for the PHD and 0.77 (95% CI: 0.68–0.87) for the HPDI. Similar associations were observed for distal colon cancer (PHD: HR 0.71, 95% CI: 0.55–0.91; HPDI: HR 0.73, 95% CI: 0.57–0.92). Associations for proximal colon cancer were slightly weaker but remained significant (PHD: HR 0.75, 95% CI: 0.61–0.94; HPDI: HR 0.86, 95% CI: 0.77–0.99). Greater adherence to the PHD and HPDI was associated with a substantially lower risk of colorectal cancer, with consistent associations across tumour subsites. These findings support the potential role of environmentally sustainable and plant-forward dietary patterns in colorectal cancer prevention and strengthen the evidence base for integrating planetary health principles into public health nutrition strategies.