How strong is the link between red meat and cancer? New study to put the evidence to the test

By Dr. Chinta SidharthanReviewed by Susha Cheriyedath, M.Sc.Mar 18 2025

With decades of conflicting studies on meat and cancer, researchers are cutting through the noise with a high-level review to determine whether red and processed meat truly increase cancer risk—or if the evidence is weaker than we think.

Study Protocol: Association of red and processed meat consumption with cancer incidence and mortality: An umbrella review protocol. Image Credit: Franck Boston / Shutterstock

Could your favorite steak or bacon be increasing your cancer risk? Various studies have linked red meat consumption to an increased risk of cancer. In a recent article published in the journal PLOS ONE, researchers from Huaqiao University and Shandong University in China proposed a comprehensive study protocol to analyze decades of research on processed and red meat consumption and its links to cancer. This protocol aims to establish a standardized method for assessing previous findings but does not present new conclusions at this stage.

Red Meat Consumption and Cancer

Red and processed meats are dietary staples worldwide, but their impact on health has been contentious for years. Studies have suggested links between these meats and various types of cancers, such as colorectal, pancreatic, and breast cancer.

In 2015, the International Agency for Research on Cancer classified processed meat as carcinogenic and red meat as "probably carcinogenic." However, inconsistencies in study methods, definitions of meat intake (e.g., grams per day vs. servings per week), and dose-response analyses have led to ongoing debate.

Previous systematic reviews have explored these associations, but few have critically examined the statistical credibility of these findings. Additionally, many studies have assessed different cancer types separately, making it difficult to draw broad conclusions.

Investigation Protocol

The researchers proposed an umbrella review to address these gaps in knowledge about the link between red meat and cancer risk. This method consolidates data from multiple meta-analyses to offer a more precise and statistically robust assessment of cancer risks associated with red and processed meat consumption.

This proposal recommended a rigorous methodology for synthesizing evidence from multiple systematic reviews and meta-analyses. The researchers suggested five major electronic databases—PubMed, Embase, Web of Science, Scopus, and the Cochrane Library—along with additional registers such as PROSPERO and INPLASY to search for reviews and meta-analyses. Only systematic reviews that focus on observational studies (cohort and case-control studies) linking red and processed meat to cancer incidence and mortality were to be included in the analysis.

To ensure a comprehensive and updated evaluation, the team also recommended incorporating new primary studies not previously included in existing meta-analyses. Furthermore, the protocol’s statistical approach involved re-performing meta-analyses using random-effects models (though fixed-effects models would be used for associations with fewer than five studies in sensitivity analyses), assessing heterogeneity, and evaluating small-study effects. This means that results from smaller studies, which may exaggerate risks, will be carefully assessed before drawing conclusions.

The credibility of evidence would be categorized (Class I being strongest, IV weakest) based on statistical significance, sample size, and potential biases. Additionally, the researchers recommend a sensitivity analysis to test the findings’ robustness and re-assessment of dose-response effects to determine how different levels of meat consumption influence cancer risks.

The protocol also suggested using AMSTAR 2, a recognized tool for evaluating systematic reviews. Additionally, the strength of associations would be graded based on factors such as bias, inconsistency, and the magnitude of effects. The researchers believe that following this proposed protocol will help determine whether the link between red and processed meat and cancer is strong, suggestive, or weak, ultimately guiding public health recommendations.

Primary Aims of the Protocol

The study aimed to clarify the degree of cancer risk associated with red and processed meat consumption. Furthermore, the researchers hypothesized that systematically analyzing previous research will help determine which types of cancer are most strongly linked to meat consumption and assess whether current dietary guidelines align with the best available evidence.

Previous studies have reported a greater risk of colorectal, pancreatic, gastric, and bladder cancers in individuals who consume high amounts of processed and red meats. However, inconsistencies in reporting and lack of uniform evidence grading have made it difficult to draw definitive conclusions. This umbrella review protocol aims to address these concerns by evaluating the robustness of existing evidence and identifying areas where more research is needed. The study does not preemptively assume that small amounts of red or processed meat pose a risk—this remains systematically reviewed.

One important aspect of the proposed protocol is the dose-response relationship assessment, which will help determine whether even small amounts of red or processed meat pose a risk or if the danger is primarily associated with excessive consumption. This review will provide a more accurate picture of how dietary choices influence cancer risk by reassessing the validity of previous findings and integrating newly published research.

Additionally, a key component of the study is its focus on epidemiological estimates from prospective cohort studies. By analyzing these studies, the researchers aim to estimate the prevalence of various cancers among populations with different levels of processed and red meat intake. This estimate will be based on cohort studies rather than case-control studies, as the latter may not provide reliable prevalence data.

The researchers stated that they are in the process of publishing the assessment results using the protocol described here and will use this framework to guide a systematic evaluation of the evidence. At this stage, no changes to dietary recommendations are being proposed.

Conclusions

In summary, the proposed umbrella review protocol could be instrumental in understanding how red and processed meat consumption affects cancer risk. By consolidating vast amounts of research and rigorously assessing evidence quality, it will provide a clearer framework for future research rather than immediate dietary guidance. While the debate on meat and cancer continues, the findings from this assessment will help determine whether existing studies provide strong, suggestive, or weak evidence regarding meat consumption and cancer risk.