Background: Findings among randomized controlled trials evaluating the effect of red meat on cardiovascular disease risk factors are inconsistent. We provide an updated meta-analysis of randomized controlled trials on red meat and cardiovascular risk factors and determine whether the relationship depends on the composition of the comparison diet, hypothesizing that plant sources would be relatively beneficial.
Methods: We conducted a systematic PubMed search of randomized controlled trials published up until July 2017 comparing diets with red meat with diets that replaced red meat with a variety of foods. We stratified comparison diets into high-quality plant protein sources (legumes, soy, nuts); chicken/poultry/fish; fish only; poultry only; mixed animal protein sources (including dairy); carbohydrates (low-quality refined grains and simple sugars, such as white bread, pasta, rice, cookies/biscuits); or usual diet. We performed random-effects meta-analyses comparing differences in changes of blood lipids, apolipoproteins, and blood pressure for all studies combined and stratified by specific comparison diets.
Results: Thirty-six studies totaling 1803 participants were included. There were no significant differences between red meat and all comparison diets combined for changes in blood concentrations of total, low-density lipoprotein, or high-density lipoprotein cholesterol, apolipoproteins A1 and B, or blood pressure. Relative to the comparison diets combined, red meat resulted in lesser decreases in triglycerides (weighted mean difference [WMD], 0.065 mmol/L; 95% CI, 0.000-0.129; P for heterogeneity <0.01). When analyzed by specific comparison diets, relative to high-quality plant protein sources, red meat yielded lesser decreases in total cholesterol (WMD, 0.264 mmol/L; 95% CI, 0.144-0.383; P<0.001) and low-density lipoprotein (WMD, 0.198 mmol/L; 95% CI, 0.065-0.330; P=0.003). In comparison with fish, red meat yielded greater decreases in low-density lipoprotein (WMD, -0.173 mmol/L; 95% CI, -0.260 to -0.086; P<0.001) and high-density lipoprotein (WMD, -0.065 mmol/L; 95% CI, -0.109 to -0.020; P=0.004). In comparison with carbohydrates, red meat yielded greater decreases in triglycerides (WMD, -0.181 mmol/L; 95% CI, -0.349 to -0.013).
Conclusions: Inconsistencies regarding the effects of red meat on cardiovascular disease risk factors are attributable, in part, to the composition of the comparison diet. Substituting red meat with high-quality plant protein sources, but not with fish or low-quality carbohydrates, leads to more favorable changes in blood lipids and lipoproteins.
Keywords: apolipoproteins; blood pressure; diet; lipids; meat; red meat.