ReviewMeat consumption and cancer risk: a critical review of published meta-analyses
Introduction
Cancer is one of the leading causes of morbidity and death around the globe, averaging approximately 14 million new cases and 8.2 million cancer-related deaths each year. Even more importantly, the number of new cancer cases is expected to rise by nearly 70% over the next two decades, up to 22 million new cases per year, which would probably make it the first cause of mortality worldwide (Stewart and Wild, 2014). The five most common types of malignancies are represented by lung, prostate, colorectal, stomach, and liver cancers in men, whereas breast, colorectal, lung, cervix and stomach cancers are the five most common types of malignancies in women, respectively (Stewart and Wild, 2014). Although cancer pathogenesis is challenging and multifaceted, it is now established that genetic and environment factors interplay to promote carcinogenesis. In particular, certain physical (e.g., ultraviolet and ionizing radiation) and biological carcinogens (viral, bacterial or parasitic infections) interact with behavioural and dietary risk factors such as obesity, low fruit and vegetable intake, lack of physical activity, tobacco and alcohol, to favour the transformation of a normal cell into a malignant cell, a phenomenon that can be particularly magnified in genetically predisposed individuals (World Cancer Research Fund, 2007).
Among the various factors, diet habits play a substantial role for increasing or reducing the risk of various cancers. Although the causal link between diet and cancer is complex and can be hardly unravelled due to the fact that conventional diets entail many different foods and nutrients, evidence is being gathered that certain foods may be more harmful than others (Bishop and Ferguson, 2015).
A reasonable amount of meat is part of a balanced humans diet, since it provides valuable nutrients such as proteins and essential amino acids, vitamins, minerals and other micronutrients (Lafarga and Hayes , 2014). In the traditional culinary terminology, meat is conventionally classified as “red” when characterized by a typical red hue, whereas “white” usually defines a lighter-coloured subtype. Although a semantic debate is still opened, the former type defines the meat of most adult mammals (i.e., cow, pork, sheep, horse), whereas the latter is typically used to identify poultry (i.e., chicken, turkey) and rabbit. The meat can be marketed fresh, immediately after slaughter, or processed by means of salting, curing, addiction of spices and non-meat additives, stuffing, fermentation, drying or smoking (Food and Agriculture Organization of the United Nations, 2015).
According to the recent statistics of the Food and Agriculture Organization of the United Nations (FAO), the current worldwide consumption of meat is as high as 311.8 million tonnes/year, and prevalently include pork (115.5 million tonnes), followed by poultry (108.7 million tonnes), beef (68.0 million tonnes) and ovine (14.0 million tonnes) (Food and Agriculture Organization of the United Nations, 2014). Importantly, the worldwide meat production is projected to double by the year 2050, especially in developing countries. Due to the development of societies, urbanization and growth in disposable income levels, the demand for processed meat will also consistently increase (Food and Agriculture Organization of the United Nations, 2014). Therefore, the impact of fresh and processed meat on human health is expected to grow exponentially in the next decades. In a recent meta-analysis including 13 cohort studies and 1,674,272 individuals (Abete et al., 2014), higher intake of processed meat was found to be a significant risk factor for all-cause (relative risk [RR], 1.22; 95% CI, 1.16–1.29) and cardiovascular (RR, 1.18; 95% CI, 1.05–1.32) mortality. A higher intake of total red meat was significantly associated with cardiovascular mortality (RR, 1.16; 95% CI, 1.03–1.32), whereas no significant association was found between all-cause death and total meat intake (RR, 1.04; 95% CI, 0.84–1.30) or total white meat (RR; 0.90; 95% CI, 0.73–1.11). These results were substantially confirmed in another meta-analysis including 9 prospective studies and 1,330,352 individuals (Larsson and Orsini, 2014), in which all-cause mortality was significantly associated with higher intake of total red meat (RR, 1.29; 95% CI, 1.24, 1.35) and processed meat (RR, 1.23; 95% CI, 1.17–1.28), but not of unprocessed meat (RR, 1.10; 95% CI, 0.98–1.22). According to this persuasive epidemiological evidence, the American Institute for Cancer Research published a public health goal, that population average consumption of red meat should be less than 300 g (11 oz) a week, very little (if any) to be processed (World Cancer Research Fund, 2007).
Therefore, to establish whether the consumption of total meat and meat subtypes may be associated with human cancer, we performed a critical review of meta-analyses that have been published so far on this topic.
Section snippets
Search methodology
We performed an electronic search on Medline and Scopus, using the keywords “meat” AND “cancer” OR “neoplasm” OR “tumor” OR “malignancy” AND “meta-analysis” OR “critical review” in “Title/Abstract/Keywords”; with no language restriction. The search was limited to recent meta-analyses; i.e.; those published in the past 10 years (between 2005 and 2015). Clinical studies; letters or commentaries; review articles with no data on cancer risk; review articles with no data on meat consumption; and
Results
The main outcome of this systematic literature search about meat intake and cancer risk is shown in Table 1, Table 2, Table 3.
Discussion
Accurate information on the potential association between meat consumption and health risk is essential for driving consumer choices, for establishing and implementing dietary recommendations, for changing diet and lifestyle behaviors, as well as for reformulating foods to minimize health hazards. A larger intake of meat, and particularly of red and processed meat, has been convincingly associated with a variety of human disorders, including cardiovascular disease (Abete et al., 2014), diabetes
Funding support
None
Conflict of interest
None.
Giuseppe Lippi born in Padova (Italy) on October 4th, 1967, currently serves as Full Professor of Clinical Biochemistry at the University of Verona and Director of the clinical chemistry and haematology laboratory of the University Hospital of Verona. He has published more than 1150 articles in peer-reviewed journals, his total Impact Factor is 4120 and the Hirsch Index (H-index) is 61. He has recently been awarded with the 2014 Management Sciences and Patient Safety Division Award of the
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Giuseppe Lippi born in Padova (Italy) on October 4th, 1967, currently serves as Full Professor of Clinical Biochemistry at the University of Verona and Director of the clinical chemistry and haematology laboratory of the University Hospital of Verona. He has published more than 1150 articles in peer-reviewed journals, his total Impact Factor is 4120 and the Hirsch Index (H-index) is 61. He has recently been awarded with the 2014 Management Sciences and Patient Safety Division Award of the American Association for Clinical Chemistry (AACC) for outstanding contributions in the field of patient safety in the clinical laboratory/healthcare industry.