Green lentils and chickpeas featured in a taco recipe by chef Michael Smith. Harvard researchers consider those ingredients high-quality plant proteins. (Tim Chin/Canadian Press)
Swapping out red meat for plant-based sources of protein reduced heart disease risks in a review of research.
For the meta-analysis on meat consumption, researchers analyzed data from 36 randomized controlled trials comparing diets with red meat with diets that replaced red meat with a variety of foods.
The studies, involving 1,800 participants, looked at diets that included poultry and fish, diets that included just fish or just chicken, diets with or without dairy, diets with more carbohydrates (like bread and cereal) and diets with plant proteins (legumes, soy, or nuts).
The focus of the paper, published in the journal Circulation, was on factors associated with heart disease: blood concentrations of cholesterol, triglycerides, lipoproteins, and blood pressure.
The study's lead author, Marta Guasch-Ferré, a research scientist at Harvard's nutrition department, and her team crunched the numbers by comparing high-meat diets to a combination of other diets. Overall, across all diets, they found no major differences in the factors associated with heart disease.
Then the researchers took a deeper dive to check the diets individually.
"We find that when red meat was substituted by high-quality plant protein sources including legumes, soy or nuts, that led to more favourable changes in blood lipids and lipoproteins compared to red meat," Guasch-Ferré said in an interview.
Legumes include beans, peas, lentils and chickpeas.
Burgers versus fries
The researchers say this explains inconsistencies found in previous studies on the effects of red meat on cardiovascular risk.
Previous research didn't take into account the composition of the comparison diet, as substituting low-quality carbohydrates did not have a positive effect on heart health, they said.
"Asking 'Is red meat good or bad?' is useless," Meir Stampfer, a professor of epidemiology and nutrition and senior author of the study, said in a release from Harvard T.H. Chan School of Public Health. "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 Harvard authors recommended that consumers follow healthy vegetarian and Mediterranean-style diets, both for their health benefits and to promote environmental sustainability.
The findings emphasize that proteins are an important aspect of a diet to reduce cardiovascular risk, said Laura Rosella, an associate professor in epidemiology at the Dalla Lana School of Public Health at the University of Toronto.
What's substituted for red meat in the diet matters, nutrition researchers say.(Eugene Hoshiko/Associated Press)
"Canada's new Food Guide encourages a range of protein sources, including beans, peas and soy products. The Food Guide also emphasizes a range of healthy choices across your diet," Rosella said in an email.
Unlike prescription drug studies that compare a medication to a placebo, researchers who study diet have to be aware that people will always replace one food with something else.
"The impact of the diet change can vary a lot depending on what is being replaced by what is taken away," said Rosella, an expert in population health research. "This is an important message for consumers, because often results from studies like this can be interpreted too simplistically to — 'don't eat this' or 'eat that' — when in fact consumers should be thinking about their overall diet and how to make that as healthy as possible across the board, including what they drink."
Randomized trials themselves can vary in quality and duration. And many more factors influence disease than what can be captured in a trial.
The meta-analysis was about cardiovascular risk factors only, not other health outcomes such as cancer or mortality.
With files from CBC's Amina Zafar
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