Can eating certain meats reduce my risk of heart disease and cancer?

Red meat is defined as beef, veal, pork, lamb, mutton, horse, or goat meat.¹ Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, and other processes with the goal of enhancing flavor or prolonging preservation. Red meat contains valuable protein and micronutrients such as B vitamins and iron. Its fat content varies. There is some evidence that the consumption of red or processed meats may have a deleterious effect on health, including cardiovascular health and an increased risk of cancer. Processing of meat can result in the formation of carcinogenic chemicals and high-temperature cooking can also produce known or suspected carcinogens.^2–7 Some studies have demonstrated that a higher intake of red meat is associated with elevations in blood pressure⁸ and cholesterol.⁹

A working group from ten countries met at the International Agency for Research on Cancer in 2015 to evaluate the available data on the carcinogenicity of red and processed meat. They assessed over 800 studies, with emphasis given to prospective cohort studies and high-quality population-based case-control studies.¹ Multiple studies reported a positive association with colorectal cancer risk and consumption of red^10,11 and processed^7,10,12–14 meat. A meta-analysis of colorectal cancer in ten cohort studies reported a significant dose-response relationship: a 17% increased risk per 100 g/day of red meat, and an 18% increased risk per 50 g/day of processed meat.¹⁵ Positive associations were also seen between red meat consumption and cancers of the pancreas and prostate, and between processed meat consumption and cancer of the stomach. On the basis of this large data review, the working group concluded that there was sufficient epidemiological evidence for the carcinogenicity of processed meat. They classified processed meat as “carcinogenic” on the basis of its association with colorectal cancer. Chance and confounding could not be ruled out with the same degree of confidence for the data on red meat. They concluded there was limited evidence for the carcinogenicity of red meat, since several high-quality studies found no clear association, and ultimately classified red meat as “probably carcinogenic”.

Pan et al. studied two cohorts from the Health Professionals Follow-up Study (n=37,698) and the Nurse’s Health Study (n= 83,644) who had no cardiovascular disease (CVD) or cancer at baseline.¹⁶ In this prospective observational study, diet was assessed at baseline from validated food history questionnaires and reassessed at 4-year intervals. Adjusting for major lifestyle and dietary risk factors, the pooled hazard ratio (HR) for CVD mortality with a one-serving per day increase in unprocessed red meat was 1.18 (95% confidence interval [CI] [1.13 – 1.23]) and for processed red meat was 1.21 (95% CI [1.13 – 1.31]). For cancer mortality the HR were 1.10 (95% CI [1.06 – 1.14]) and 1.16 (95% CI [1.09 – 1.23]), respectively. Based on the dietary data, they also estimated that substituting one serving per day of other proteins (fish, poultry, nuts, legumes, low-fat dairy, and whole grains) for one serving per day of red meat was associated with a 7% to 19% lower mortality risk.

Micha et al. conducted a systematic review and meta-analysis of available research on the association of red meat consumption with coronary heart disease (CHD), stroke, and diabetes risk among healthy adults.¹⁷ Twenty studies (total n= 1,218,380) met their inclusion criteria, of which 17 were prospective cohort studies and three were case-control studies. Based on data from five studies, processed meat was associated with a 42% higher risk of CHD. The relative risk (RR) per 50 gram serving per day was 1.42 (95% CI [1.07 – 1.89], p=0.04). Red meat was not associated with CHD based on the four studies that included the relevant data.

Another meta-analysis was conducted by Kim et al. to analyze the association between red, processed, and white meat with the incidence of gastric cancer.¹⁸ The analysis included 43 studies, 11 cohort and 32 case-control studies (n=1,764,894). The RR for the development of gastric cancer was 1.41 (95% CI [1.21 – 1.66]) among the highest consumers of red meat, and 1.57 (95% CI [1.37 – 1.81]) among the highest consumers of processed meats compared to the lowest consumers. White meat consumption was negatively associated with gastric cancer risk (RR 0.80, 95% CI [0.69 – 0.92]).

Sinha et al. conducted a prospective study of the relationship between meat consumption and mortality.¹⁹ They mailed questionnaires to 3.5 million AARP members and more than one-half million responded. During the 10-year follow-up, 47,976 male deaths and 23,276 female deaths occurred. The questionnaire sought data on diet as well as other lifestyle issues that might confound the relationship. These included personal and family history of cancer, body mass index, smoking history, physical activity, alcohol use, fruit and vegetable consumption, and hormone therapy among women. These confounding variables were considered when computing adjusted HR. The adjusted HR for overall mortality during 10 years of follow-up for men and women in the highest quintile of red meat consumption compared to those in the lowest quintile was 1.31 (95% CI [1.27 – 1.35]) and 1.36 (95% CI [1.30 – 1.43]), respectively. For processed meat consumption, the comparable HR were 1.16 (95% CI [1.12 – 1.20]) and 1.25 (95% CI [1.20 – 1.31]). In addition, comparing highest and lowest quintiles, the HR for the risk of CVD was also elevated for men and women who consumed red meat (1.27, 95% CI [1.20 – 1.35] and 1.50, 95% CI [1.37 – 1.65]) and processed meat (1.09 95% CI [1.03 – 1.15] and 1.38 95% CI [1.26 – 1.51]). Of note, comparing the highest and lowest quintiles of men who consumed white meat, there was an inverse relationship for total mortality (HR 0.92, 95% CI [0.89 – 0.94], p<0.0001) and cancer mortality (HR 0.84, 95% CI [0.80 – 0.88], p<0.001). There was a small increase in risk for CVD mortality in men with a higher intake of white meat (HR 1.0, 95% CI [1.00 – 1.11], p=0.009). Comparable HRs for women consuming white meat were 0.92 (95% CI [0.88 – 0.96], p<0.005) for all mortality, and 0.89 (95% CI [0.83 – 0.95], p=0.001) for cancer mortality. There was no significant relationship between white meat consumption and CVD mortality among women.

Kappeler et al. analyzed data from 17,611 participants in the Third National Health and Nutrition Examination Survey (NHANES III) and found no significant association between the consumption of red meat and mortality.²⁰ During the 15-year follow-up period there were 3,683 deaths. There was a tendency toward an inverse relationship between men who consumed white meat and the risk of all-cause mortality (p for trend=0.02), but no such association with women.

The magnitude of the effects is small. A separate analysis suggested a risk reduction on 11 people per thousand in ten years associated with decreasing red meat intake by three servings per week.²¹

While there are limitations to any prospective cohort or case-control study that is not randomized or representative of the population as a whole, the data gathered to date suggests that consumption of white meat or other proteins in place of red or processed meat will result in a measurable improvement in the risk of all-cause mortality. At the very least the data suggests further research is needed to clarify and quantify the relationship between meat subtypes and specific causes of mortality.

^References

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