Plant-based foods confer mortality, CHD benefits
Two studies presented at the American Heart Association Epidemiology, Prevention, Lifestyle and Cardiometabolic Health Scientific Sessions found that plant-based foods confer long-term health benefits.
In one study, elevated plant protein intake was associated with lower mortality, as was replacing animal protein with plant protein.
In another, red meat intake, especially processed red meat intake, was associated with elevated CHD risk, which was mitigated by substituting high-quality plant-based foods.
Plant protein intake
To test a hypothesis that substituting plant protein for carbohydrates and animal protein would confer lower mortality, Zhilei Shan, MD, PhD, postdoctoral research fellow in the department of nutrition at Harvard T.H. Chan School of Public Health, and colleagues analyzed 37,233 adults aged 20 years or older with dietary recall data from eight National Health and Nutrition Examination Survey cycles between 1999 and 2014. Outcomes of interest were all-cause mortality, CHD mortality and cancer mortality.
“The associations of animal and plant protein intake with mortality remain inconsistent,” Shan told Healio. “Sources of animal and plant proteins varied substantially among the different populations in these studies, and few studies have investigated the isocaloric substitution of plant protein for total and various sources of animal protein in relation to mortality. We used data from a nationally representative sample of U.S. adults and investigated the isocaloric substitution of plant protein for total carbohydrate and various sources of animal protein in relation to risk of mortality.”
During 297,768 person-years of follow-up, there were 4,866 deaths, including 849 from CHD and 1,068 from cancer.
After multivariable adjustment, there was no association between animal protein intake and mortality. However, compared with those in the lowest quintile on plant protein intake, those in the highest quintile had a lower risk for all-cause mortality (adjusted HR = 0.73; 95% CI, 0.61-0.88), Shan and colleagues found.
In addition, there were trends toward the highest quintile of plant protein intake having a lower risk for CHD mortality (aHR = 0.71; 95% CI, 0.48-1.05) and cancer mortality (aHR = 0.74; 95% CI, 0.53-1.04) compared with the lowest quintile, according to the researchers.
When isocalorically replacing 5% of energy from total animal protein with plant protein, risk for all three mortality outcomes was lower (aHR for all-cause mortality = 0.49; 95% CI, 0.32-0.74; aHR for CHD mortality = 0.51; 95% CI, 0.28-0.95; aHR for cancer mortality = 0.53; 95% CI, 0.28-1), according to the researchers.
All-cause mortality was also lower when substituting 2% of energy from plant protein for protein in unprocessed red meat (aHR = 0.74; 95% CI, 0.63-0.87), when substituting 2% of energy from plant protein for protein in processed meat (aHR = 0.68; 95% CI, 0.53-0.89), when substituting 2% of energy from plant protein for total dairy (aHR = 0.74; 95% CI, 0.58-0.94) and when substituting 1% of energy from plant protein for seafood (aHR = 0.86; 95% CI, 0.79-0.93), Shan and colleagues found.
“The underlying public health message is that replacing animal protein with plant protein sources is associated with a lower risk of death,” Shan told Healio. “These findings are in line with the U.S. dietary guidelines that advocate for a plant-based dietary pattern for lowering chronic disease risk. People should consider replacing animal protein sources such as red and processed meat with healthy plant proteins such as nuts, legumes, and whole grains.”
Red meat and CHD
Laila Al-Shaar, PhD, postdoctoral research fellow in the Harvard T.H. Chan School of Public Health’s Cardiovascular Epidemiology Program, and colleagues investigated the association between total, unprocessed and processed red meat consumption and the risk for CHD.
“The relation of red meat to risk of CHD is of great interest, and the observed associations are likely to depend on the foods to which red meat is compared,” Al-Shaar told Healio. “Analyses that fail to specify comparison foods are by default mainly comparing red meat with these less healthy sources of calories. Because of this, our research team conducted this study and used a substitution analysis approach to understand how replacing red meat (total, processed or unprocessed red meat) with another protein-rich food was associated with the risk of heart disease.”
They analyzed 43,259 men from the Health Professionals Follow-up Study between 1986 and 2012 who had no history of CVD or cancer and who updated a food frequency questionnaire every 4 years.
During 932,968 person-years of follow-up, there were 4,148 new CHD cases, of which 1,680 were fatal, according to the researchers.
After adjustment for dietary and nondietary risk factors, total red meat intake was associated with elevated CHD risk (aHR for one serving per day increment = 1.08; 95% CI, 1.01-1.14), as was processed red meat intake (aHR for one serving per day increment = 1.13; 95% CI, 1.03-1.22).
In addition, substituting one serving per day high-quality plant foods such as nuts, legumes, soy, whole grains and dairy for one serving per day of red meat resulted in CHD risk reductions of 10% to 47%, Al-Shaar and colleagues found.
Substituting nuts for processed red meat reduced fatal CHD risk by 17% (95% CI, –27 to –6), whereas substituting whole grains for processed red meat reduced fatal CHD risk by 48% (95% CI, –60 to –32), according to the researchers.
“This study adds to the substantial body of evidence that higher consumption of red meat, especially processed red meat, increases the risk of heart disease,” Al-Shaar said in an interview. “Choosing more healthful sources of protein such as high-quality plant-based protein foods is associated with lower risk of heart disease as compared to red meat. Our findings support current recommendations to limit consumption of red meat and suggest that high-quality plant-based proteins such as nuts, legumes and soy are good alternatives. This would potentially provide more specific guidance for healthier alternatives for those planning to cut down their red meat intake.” – by Erik Swain
References:
Al-Shaar L, et al. Abstract P512.
Shan Z, et al. Abstract P510. Both presented at: American Heart Association Epidemiology, Prevention, Lifestyle and Cardiometabolic Health Scientific Sessions; March 3-6, 2020; Phoenix.
Disclosures: The authors of both studies report no relevant financial disclosures.
Perspective
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These studies are critical and much-needed confirmation of data published from both American (NIH/AARP, Adventists Health Studies 1 and 2, Nurses Health Study/Health Professional Follow-up) and Japanese (Japan Public Health Center) cohorts.
The bottom line should be shared with physicians, their families and their patients: if you’re not eating a completely whole-food vegetarian diet, please look at the mortality associated with consumption of animal products. There is a lot of recent basic science clarity about why mortality increases with a nonvegetarian diet. Eating animal protein is associated with more saturated fat, cholesterol, heme iron, trimethylamine oxide (TMAO), inflammation (C-reactive protein) and sulfur-containing amino acids (cysteine and methionine). In addition, the development of diabetes, cholesterol, hypertension, peripheral artery disease, erectile dysfunction, stroke and MI all are increased by consumption of animal products.
Technically, there are still knowledge gaps. There are people, albeit some with financial conflicts, who say that the existing data are weakened by the fact that they are observational in nature and not prospective and randomized. This potentially introduces some “healthy user” bias. Only a large prospective randomized trial can settle this. However, is it frequently stated that there are enough small trials to not harm human health by randomly assigning some to increased mortality. While this may be the case, our professional prevention guidelines will rarely give a Class I recommendation to nonrandomized datasets.
It’s not just animal protein at issue. An unhealthy plant-based diet (sugary items, fried foods, juices, refined grains, etc) is actually worse than an animal-laden diet. But for those who are doing plant-based nutrition and doing it well, don’t forget to take a B12 supplement as needed.
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