Animal source foods: the health controversy

Dietary recommendations often advocate for limiting the consumption of animal source foods, particularly red and processed meats, as well as animal fat. Some authors even categorize animal source foods as 'less healthy' compared to plant-derived foods, and equate red meat with unhealthy foods like sugar. However, contrary to claims made by vocal public health nutritionists, these recommendations lack consensus and unanimous scientific support. Some experts have expressed concerns, especially for populations with high nutritional needs. They argue that these recommendations rely on incomplete data and problematic interpretations. Moreover, overly restricting animal source foods may lead to nutrient deficiencies that outweigh any potential risk of chronic disease.

Observational studies suggest that high consumption of some animal source foods may be associated with slightly increased health risks, but these findings are debatable and suffer from confounding and bias. Moreover, human intervention studies do not strongly support these claims, and biochemical studies lack clear mechanisms to explain them. Despite these uncertainties, observational studies often embed causal messages and recommendations in their findings, which can undermine the credibility of nutritional sciences. Researchers, however, tend to be more nuanced than policymakers, by acknowledging the limitations and potential biases in their findings and cautioning against overinterpretation due to heterogeneity and residual confounding. The WHO/IARC panel investigating the link between red meat and colorectal cancer also emphasized the possibility of chance, bias, or confounding and did not establish red meat consumption as a cancer cause.

Various experts have criticized the recommendations made by organizations such as the WCRF, WHO/IARC, EAT-Lancet Commission, Nordic Nutritional Recommendations, and Global Burden of Diseases consortium. Some concerns include issues with data quality and weak evidence for associations with diseases like cancer, diabetes, and heart disease. The GRADE system, a widely respected method for evaluating epidemiological data, suggests there is 'low' to 'very-low' certainty evidence that reducing red and processed meat intake leads to benefits in terms of cancer mortality, cardiometabolic outcomes, and all-cause mortality. As a result, it weakly recommends that adults maintain their current consumption of these meats, emphasizing individual decision-making based on absolute effect estimates. Additionally, the PURE study, a large global dietary cohort, suggests that unprocessed red meat should not be a primary target for health concerns and may be part of healthy dietary patterns.

The reporting of 'relative' risks associated with the intake of animal source foods in relation to health outcomes often leads to overstatements and sensationalism. These values are frequently presented without mentioning the 'absolute' risk, which can create exaggerated interpretations, especially among non-experts. Dietary guidelines also tend to overlook or downplay the very small absolute risk reductions that come with dietary changes. For example, an 18% relative risk increase for colorectal cancer linked to high processed meat consumption may sound alarming, but its corresponding absolute risk increase is only 1%. To put it differently, the likelihood of someone not developing colorectal cancer during their lifetime would only shift from 94% to 93% with such a dietary change. Moreover, the risk increase is based on low-certainty evidence and may as well be an artefact due to bias.