Objectives: To evaluate the empirical evidence and models cited by the Nordic Nutrition Recommendations of 2023 (NNR2023) in support of their recommended consumption of ≤350 grams/week of unprocessed red meat (RM) based on association with colorectal cancer (CRC).
Methods: We fitted empirical DR models (EMP) to the studies included in two systematic reviews (SRs) selected by NNR2023 on the RM-colorectal cancer (CRC) association- the World Cancer Research Fund CRC continuous update project from 2018 (WCRF) and the burden of proof study (BoP) (Lescinsky et al 2022). We compared the predicted relative risks (RR) at different consumption levels between these EMP and the models reported by the two SRs. The SR’s models included parametric assumptions including linearity/non-linearity, monotonicity, and between-study heterogeneity uncertainty.
Results: Twenty-one studies (20,604,188 patient-years) were analyzed. We found no significant association (RR=1.04, 0.99-1.09) between 350g/week of RM and CRC using the EMP, in agreement with the least restrictive models reported by BoP (RR=1.11 (0.89-1.38)) and WCRF (RR= 1.01(0.96-1.07)) with between-study heterogeneity, and neither linearity nor monotonicity imposed). The RM-CRC association was significant at 350 g/week only under restricting assumptions such as monotonicity RR=1.3(1.01-1.64), and linearity RR=1.06(1.00-1.12), and omitting between-study heterogeneity (1.11 (1.05-1.19)). Furthermore, the EMP model shows no significant empirical association under 567 g/week in the studies used by NNR2023.
Conclusions: The evidence cited by NNR2023 do not support a consumption restriction of ≤350 grams/week of RM due to CRC, and other studies omitted by NNR2023 do not support association between RM and CRC. We show that model assumptions rather than empirical evidence drive this recommendation. Model uncertainty should be explicitly incorporated in food-based dietary guidelines.
