• Research Review
• Journal Review

Authors: R Micha, S Wallace, D Mozaffarian

Reference: Circulation. 2010; 121: 2271-2283
http://circ.ahajournals.org/cgi/content/short/121/21/2271

Reviewer: Robert Goldberg, PhD, Contributing editor, ProCor; Professor of Medicine and Epidemiology, Division of Cardiovascular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA

Reviewer comments: The role of the type of diet one consumes, individual dietary factors, and select nutrients in the development of coronary heart disease (CHD) and other chronic diseases of major health importance has been extensively discussed and debated for several decades. While the importance of excessive dietary fat in the development of CHD and stroke has been suggested by numerous epidemiologic studies, the effects of meat consumption on CHD and other chronic diseases, as well as type of meat consumed, are less well established. The potentially adverse effects associated with excessive meat consumption are thought to be related to its effects on serum total and LDL-cholesterol levels and possibly other lipid or lipoprotein fractions. Even though recent US dietary guidelines recommend that the consumption of red and processed meat should be moderated, relatively limited data are available to support more specific recommendations about the actual amount of meat to be consumed, or type of meat, namely red versus processed meats that Americans should eat to reduce their risk of major chronic diseases.

The results of the present carefully performed summary overview suggest that the consumption of processed meats, but not red meats, is associated with an increased risk for CHD and diabetes; on the other hand, due to the relative lack of data and few studies in this area, no firm conclusions could be drawn about the association between meat intake and the risk of stroke.

The present findings suggest that men and women should be particularly encouraged to eat less processed meats as part of a heart healthy diet and to consume meat, in general, in moderation. Processed meats are often quite high in their sodium content as well as use of nitrate preservatives reinforcing the benefits of consuming lesser amounts of these foods such as hot dogs, bacon, and cured meats. On the other hand, a number of gaps exist in our knowledge base which does not allow for more specific recommendations to be provided.

A well-crafted advertisement had been utilized in the past by one of the world's largest hamburger chains asking the question "Where's the beef?" in criticizing their competition's hamburgers, both in terms of quality and size. The results of the present study suggest that while the consumption of meat need not be abandoned, the "beef" might be replaced by other less atherogenic sources of protein and dietary pleasure including fish, grains, nuts, legumes, and fresh fruit and vegetables as part of an overall heart healthy diet. Consumption of these heart healthy food sources may also help Americans reduce their burgeoning waistlines.

Purpose of study: To provide a summary overview of the association between meat consumption and the risk of CHD, stroke, and diabetes.

Location of study: Boston, MA

Study design: Systematic review

Results: The authors carried out a systematic overview of observational studies and randomized-controlled trials (RCTs) that examined the association of red, processed, or total meat consumption with the development of either CHD, stroke, or diabetes mellitus.

A total of 95 full-text articles were obtained after an extensive search of the published literature using a variety of search terms. After applying various exclusion criteria, a total of 20 studies were identified which were summarized in the present publication. These investigations included 17 prospective cohort studies and three case-control studies; no randomized trials were identified. These 20 investigations were performed in the US (n=11 studies), Europe (n=6), Asia (n=2), and Australia (n=1). A total of 1,218,380 persons were included in these studies in which 23,889 cases of CHD developed, 10,797 cases of diabetes mellitus, and 2,280 cases of stroke.

The majority of studies included in this overview used food frequency questionnaires to quantify meat consumption and extent of adjustment for several potentially confounding variables differed between the studies included. Relative risks of several chronic diseases were calculated and various modeling approaches were utilized.

In examining the association between the intake of meat and the development of CHD in nine cohort and case-control studies, consumption of red meat was not associated with the development of CHD (RR=1.00; 95% CI 0.81,1.23) per daily serving). On the other hand, the number of daily servings of processed meat (RR=1.42; 95% CI 0.94,1.89) and total meat consumption (RR=1.27; 95% CI 0.94,1.72) were associated with a higher risk of developing CHD.

In examining the association between meat intake and the development of diabetes mellitus, seven studies provided adequate data to assess this association. While the level of statistical significance varied depending on the type of meat consumed, daily servings of red meat (RR 1.16; 95% CI 0.92,1.46), processed meat (RR=1.19; 95% CI 1.11,1.27), and number of total daily meat servings (RR=1.12; 95% CI 1.05,1.19) were associated with an increased risk of developing diabetes. The consumption of bacon and hot dogs was associated with a particularly high risk of developing diabetes.

Finally, in examining the association between red, processed, or total meat consumption and the development of total stroke or stroke subtypes, only three cohort studies provided adequate data to assess this relationship. In general, there was a slightly increased risk of stroke with various types of meat consumed, but these data were difficult to interpret given the small number of studies included and between study heterogeneity.