Scientific Evidence Submissions: IARC

Case Study: Mechanisms of Dietary BaP Exposure in Colorectal Cancer (July 29, 2015)
Consumption of polycyclic aromatic hydrocarbons (PAHs) has been proposed as a mechanism by which foods cooked via high temperature grilling could increase human risk for colorectal cancer. However, this submissions highlights the evidence from recent reviews that have failed to find sufficient evidence directly linking PAH consumption from red meat with colorectal cancer. This submission outlines findings from a systematic review of the mechanistic evidence relating dietary exposure of benzo[a]pyrene (BaP), a specific PAH, to human colon carcinogenesis.

Based on a comprehensive analysis of the available data, the review concludes that a critical research gap exists regarding mechanistic evidence linking BaP exposure from the diet and colorectal cancer. In addition, the review of the data indicates that the evidence is weak and inadequate in both humans and animals concerning the mechanistic relationship between dietary BaP exposure and human colorectal cancer.

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Systematic Review: Mechanisms of Dietary Heme Iron Intake in Colorectal Cancer (August 28, 2015)
Although the human observational data linking red meat and various cancers remain inconclusive, a number of potential mechanisms have been hypothesized related to the role of red and processed meat and the development of various cancers. One proposed mechanism is related to the naturally occurring essential nutrient, iron, which is a component of heme iron as it occurs in red meat. The European Food Safety Authority (EFSA) recently reiterated earlier conclusions that iron is an essential nutrient, evidence is insufficient to establish a tolerable upper intake level for iron, and insufficient data exists to link total dietary iron to increased risk of colorectal cancer (CRC).

In addition, this systematic review identified numerous methodological limitations and inconsistencies in the evidence, noting several critical research gaps on this topic. Importantly, the type of heme iron supplemented in animal diets in the research, as surrogates for naturally occurring heme iron from hemoglobin and myoglobin in red and processed meat, independently affects outcomes. Moreover, none of the various mechanisms tested by the studies included in this review are supported by evidence sufficient to confirm a mechanistic link between red meat and CRC. The review concludes that evidence is weak and inadequate in both humans and animals related to a mechanistic relationship between dietary heme iron, from red and processed meat, and the development of human CRC.

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Evidence regarding Benzo[a]pyrene (BaP) content in foods is weakened by critical research gaps that call into question the ability to assess BaP as a mechanistic link associated with red and processed meat and cancer (September 3, 2015)
Benzo[a]pyrene (BaP) is the most studied polycyclic aromatic hydrocarbon (PAH) and is found in foods as a result of both environmental contamination and exposure to smoke and/or flame during processing or cooking. While red and processed meats contain varying amounts of BaP and other PAHs, which may increase with various cooking methods, epidemiologic evidence fails to clearly demonstrate a significant relationship between BaP intake from meat and colorectal cancer risk.

This submission highlights the BaP content in the current food supply as the result of various cooking methods and as the content released in cooking fumes. For example: with the exception of fish, pan and deep fried meats do not contain significant amounts of BaP. In addition, BaP concentrations in plant-based foods, in particular bread and/or toasted bread, are equal to or exceed those reported for well-done meats.

The review notes that the evidence regarding BaP content in foods is weakened by critical research gaps that call into question its relevance and the ability to assess BaP as a mechanistic link associated with red and processed meat and cancer. For example, shortfalls and barriers to accurately assess exposure to BaP from all foods significantly limits the ability to draw conclusions in this area, and there is a need to update existing databases to better evaluate exposure to BaP from red and processed meats, as well as other foods.

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Systematic review: Evidence is weak and inadequate in both humans and animals concerning the mechanistic relationship between dietary HCA exposure from red and processed meat and human prostate, breast, and colorectal cancer (September 10, 2015)
Population-based studies fail to demonstrate consistent and convincing evidence for a relationship between heterocyclic amines (HCAs), when consumed as part of a diet, and cancer risk. This submission highlights results of a systematic review of the evidence to determine whether consumption of HCAs in red and processed meat as a result of cooking could be mechanistically linked with cancer risk in humans.

The review of the evidence shows that interactions between individual genetic factors, estimations of HCA intake from red and processed meat, and cancer outcomes were inconsistent. In addition, due to limitations of estimating dietary HCAs with existing databases and lack of in-study validation, any mechanistic links of dietary HCAs with cancer in humans are inconclusive. The submission concludes that, based on the review, evidence is weak and inadequate in both humans and animals concerning the mechanistic relationship between dietary HCA exposure from red and processed meat and human prostate, breast and colorectal cancer.

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Intake of Red and Processed Meat in the United States (September 10, 2015)
“Meat” is a broad food category that is ambiguous in nutritional epidemiology. This submission provides the latest evidence on consumption of red and processed meat in the United States, to support an accurate assessment of the data, given possible limitations of international databases. Key points noted include:

  • The average intake of fresh red meat in the United States is 44.2 g per day (WWEIA, 2011-2012).
  • The average intake of processed (cured) meat is 27.8 g per day. (WWEIA, 2011-2012)
  • Usual U.S. adult consumption of red and processed meat is within, and often lower, than that reported in observational studies of the Mediterranean-style dietary pattern, which is recognized for its reduction in chronic disease risk. (Romaguera et al., 2009; Buckland et al., 2011)

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Weak and limited evidence regarding heterocyclic amine (HCA) content in foods limits the ability to estimate human HCA exposure and calls into question the ability to assess HCAs as a mechanistic link associated with red and processed meat and cancer (September 11, 2015)
This submission focuses on the content of heterocyclic amines (HCAs), also known as heterocyclic aromatic amines (HAAs), in various foods during cooking. However, the relevance and accuracy of the available evidence is significantly limited by research gaps. For example, despite the availability in the past decade of numerous quantitative reports of HCAs in various foods, the two most readily available HCA estimation databases have not been updated since at least 2003. Continuous updating of food HCAs analyses is required, as well as standardization of cooking methods and terminology, to accurately assess HCA content and impact.

The submission concludes that the failure to update HCA databases to reflect the current food supply, detection methodology and equipment, world-wide food availability and preparation techniques prevents the accurate assessment of human exposure to HCAs. These significant evidence limitations call into question the relevance of HCAs exposure as a possible mechanism associated with cancer risk for red and processed meat intake.

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