Based on available evidence, it is very difficult to quantify how much red meat can be safely consumed without raising one’s risk for heart disease and cancer. Randomized controlled trials (RCTs), if available would provide the strongest evidence that a specific lifestyle choice is associated with a specific disease. It is difficult, however, to develop such a trial that can isolate a single dietary component, such as red meat, to prove it is the culprit that is raising a given risk. The duration of such a study needed to prove an increased risk of cancer or heart disease is also an enormous challenge. Consequently, few such RCTs exist that can quantify the risk of developing heart disease or cancer associated with red meat consumption.1 One alternative approach is to examine the effect of red meat on known risk factors for these diseases.
Guasch-Ferre et al. conducted a meta-analysis of 36 RCTs (total n=1803) that compared diets that included red meat with diets that replaced red meat with a variety of other foods.2 The comparison diets studied were stratified into:
- high-quality plant protein sources (legumes, soy, nuts)
- chicken/poultry/fish
- fish only
- poultry only
- mixed animal poultry sources (including dairy)
- carbohydrates (low quality refined grains and simple sugars
- a usual diet.
The random-effects meta-analyses examined the diets’ effects on cardiovascular risk factors and found no significant differences between the red meat diets and all other diets combined with respect to changes to blood cholesterol or blood pressure.2 However, substituting red meat with high-quality plant protein sources, and not with fish or low-quality carbohydrates, led to more favorable and statistically significant changes in total cholesterol and low-density lipoprotein cholesterol (LDL-C). Red meat led to lesser decreases in LDL-C (weighted mean difference [WMD] 0.264 mmol/L, 95% confidence interval [CI] [0.144 – 0.383], p<0.001) and total cholesterol (WMD 0.264 mmol/L, 95% CI [0.144 – 0.383], p<0.001) compared to a high-quality plan protein diet. The authors emphasize that the evidence suggests the risk of red meat consumption on cardiovascular risk factors depends on the diet to which it is compared. Eliminating red meat from the diet and substituting it with an unhealthy alternative may not lower the risk of heart disease.
Bouvard et al. analyzed data from 800 epidemiological studies and summarized what is known about the carcinogenicity of red meat.3 The risk associated with consuming red meat varies by the type of cancer studied. The strongest evidence links red meat consumption with colorectal cancer risk. Of 14 studies that provided data on red meat risk and colorectal cancer, a positive association was found in seven studies when comparing high red meat consumption with low red meat consumption. In a meta-analysis of the relevant studies, a 17% increased risk of colorectal cancer (95% CI [1.05 – 1.31]) was found for each 100 g of red meat consumed per day. Positive associations were also seen with red meat consumption and cancers of the pancreas and prostate. However, the authors could not rule out that bias, confounding, and chance with confidence for data linking red meat consumption to cancer. Since several high-quality studies found no clear association, they 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.4 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% 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 their 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.
Zeraatkar et al. conducted a systematic review and meta-analysis of cohort studies that examined red meat consumption and the risk of all-cause mortality, cardiovascular disease, stroke, diabetes, and anemia.5 The quantitative analysis included 61 reports (total n=4.2 million participants). Follow-up periods ranged from 2 to 28 years. Based on these meta-analyses, they estimated that reducing unprocessed red meat consumption by three servings per week lowered the risk of all-cause mortality (relative risk [RR] 0.93, 95% CI [0.87 – 1.00]), cardiovascular mortality (RR 0.90, 95% CI [0.88 – 0.91]), and myocardial infarction (RR 0.93, 95% CI [0.87 – 0.99]). Although the authors caution that these reductions in risk are based on lower-quality evidence than an RCT could provide, the results do suggest that lowering red meat consumption is likely to reduce your risk of cardiovascular disease, consistent with results from other observational analyses.6,7
Han et al. conducted a similar analysis of cohort studies that examined the effect of red meat consumption on overall cancer mortality (56 cohorts with over 6 million participants).8 A reduction of three servings per week of red meat was associated with a small overall reduction in lifetime risk of cancer mortality (RR 0.93, 95% CI [0.91 – 0.94]).
Zhong et al. pooled data from six prospective cohort studies (total n= 29,682) to measure the additional risk effected by adding two servings per week of various protein sources, including red meat.9 Each additional two servings per week of unprocessed red meat increased the risk of incident CVD by 3% (absolute risk difference [ARD] 0.62%). Further, each additional two servings per week increased the risk of all-cause mortality by 3% (ARD 0.76%) over 30 years of follow-up. An advantage of this study was the standardization of the food history data to minimize the heterogeneity among the various cohorts studied. While the effect sizes were small, the study supports the recommendation that lowering one’s consumption of red meat can lower risk.
The data gathered to date suggests that consumption of other proteins in place of red meat will result in a small but measurable improvement in the risk of all-cause mortality, cardiovascular mortality, and some types of cancer. How much to reduce one’s intake of red meat, and whether eliminating red meat completely is recommended cannot be determined from the available evidence.
References
- Zeraatkar D, Johnston BC, Bartoszko J, et al. Effect of lower versus higher red meat intake on cardiometabolic and cancer outcomes: a systematic review of randomized trials. Ann Intern Med 2019; 171 (10): 721-731.
- Guasch-Ferre M, Satija A, Blondin SA, et al. Meta-Analysis of randomized controlled trials of red meat consumption in comparison with various comparison diets on cardiovascular risk factors. Circulation 2019; 139 (15): 1828-1845.
- Bouvard V, Loomis D, Guyton KZ, et al. Carcinogenicity of consumption of red and processed meat. Lancet Oncol 2015; 16 (16): 1599-1600.
- Pan A, Sun Q, Bernstein AM, et al. Red meat consumption and mortality: results from 2 prospective cohort studies. Arch Intern Med 2012; 172 (7): 555-563.
- Zeraatkar D, Han MA, Guyatt GH, et al. Red and processed meat consumption and risk for all-cause mortality and cardiometabolic outcomes: a systematic review and meta-analysis of cohort studies. Ann Intern Med 2019; 171 (10): 703-710.
- Micha R, Wallace SK, Mozaffarian D. Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis. Circulation 2010; 121 (21): 2271-2283.
- Wang X, Lin X, Ouyang YY, et al. Red and processed meat consumption and mortality: dose-response meta-analysis of prospective cohort studies. Public Health Nutr 2016; 19 (5): 893-905.
- Han MA, Zeraatkar D, Guyatt GH, et al. Reduction of red and processed meat intake and cancer mortality and incidence: a systematic review and meta-analysis of cohort studies. Ann Intern Med 2019; 171 (10): 711-720.
- Zhong VW, Van Horn L, Greenland P, et al. Associations of processed meat, unprocessed red meat, poultry, or fish intake with incident cardiovascular disease and all-cause mortality. JAMA Intern Med 2020; 180 (4): 503-512.
