Diets that replaced red meat with healthy plant proteins led to decreases in risk factors for cardiovascular disease (CVD), according to a study from Harvard TH Chan School of Public Health and Purdue University. The study is the first meta-analysis of randomised controlled trials examining the health effects of red meat by substituting it for other specific types of foods.
“Previous findings from randomised controlled trials evaluating the effects of red meat on cardiovascular disease risk factors have been inconsistent. But our new study, which makes specific comparisons between diets high in red meat versus diets high in other types of foods, shows that substituting red meat with high-quality protein sources lead to more favourable changes in cardiovascular risk factors,” said Marta Guasch-Ferré, research scientist in the department of nutrition and lead author of the study.
The study included data from 36 randomised controlled trials involving 1,803 participants. The researchers compared people who ate diets with red meat with people who ate more of other types of foods (chicken, fish, carbohydrates, or plant proteins such as legumes, soy, or nuts), looking at blood concentrations of cholesterol, triglycerides, lipoproteins, and blood pressure – all risk factors for CVD.
The study found that when diets with red meat were compared with all other types of diets combined, there were no significant differences in total cholesterol, lipoproteins, or blood pressure, although diets higher in red meat did lead to higher triglyceride concentrations than the comparison diets. However, researchers found that diets higher in high-quality plant protein sources such as legumes, soy, and nuts resulted in lower levels of both total and LDL (“bad”) cholesterol compared to diets with red meat.
The results are consistent with long-term epidemiologic studies showing lower risks of heart attacks when nuts and other plant sources of protein are compared to red meat, the authors said. The findings also suggest that the inconsistencies found in prior studies regarding the effects of red meat on cardiovascular risk factors may be due, in part, to the composition of the comparison diet. They recommended that future studies take specific comparisons into account.
“Asking ‘Is red meat good or bad?’ is useless,” said Meir Stampfer, professor of epidemiology and nutrition and senior author of the study. “It has to be ‘compared to what?’ If you replace burgers with cookies or fries, you don’t get healthier. But if you replace red meat with healthy plant protein sources, like nuts and beans, you get a health benefit.”
The authors recommended adherence to healthy vegetarian and Mediterranean-style diets, both for their health benefits and to promote environmental sustainability.
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.
Marta Guasch-Ferré, Ambika Satija, Stacy A Blondin, Marie Janiszewski, Ester Emlen, Lauren E O’Connor, Wayne W Campbell, Frank B Hu, Walter C Willett, Meir J Stampfer