In a recent study published in BMC Medicine, researchers conducted a meta-analysis to evaluate the effects of replacing animal-based foods with plant-based alternatives on cardio-metabolic health and all-cause mortality.
The prevailing food system, heavily reliant on animal-based products, significantly strains Earth’s resources and exacerbates climate change, compromising food quality and availability.
This system, along with dietary habits rich in animal products, particularly red and processed meat, is a major contributor to non-communicable diseases like cardiovascular diseases (CVD) and type 2 diabetes (T2D), which are leading causes of death globally.
As a response, shifting dietary patterns towards plant-based foods has emerged as a key strategy. This shift benefits planetary health by reducing environmental impact and lowering the risk of T2D, CVD, and premature mortality.
Conversely, the environmental burden and health risks associated with animal-based food production and consumption are well-documented. In light of this, replacing animal-based foods with plant-based alternatives presents a viable solution.
Epidemiological studies have shown that such replacements can decrease the risk of CVD, T2D, and mortality.
Further research is needed to understand the full impact of replacing animal-based foods with plant-based alternatives on cardiometabolic health outcomes and mortality, as existing studies have not fully explored this substitution and its potential benefits on human health and the environment.
The research team pre-registered their protocol at International Prospective Register of Systematic Reviews (PROSPERO). It adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines for systematic reviews and meta-analyses.
All stages of the review process were independently conducted by at least two investigators, with disagreements resolved through consensus. Although there were no methodological deviations from the protocol, all-cause mortality was added to the outcomes due to its significant contribution to global deaths.
The team conducted a comprehensive literature search across MEDLINE, Embase, and Web of Science until December 2021, using predefined terms without applying any filters. They also examined reference lists of relevant publications and updated their search in March 2023.
Eligible studies included those that conducted substitution analyses of animal-based foods with plant-based alternatives and investigated cardiometabolic health outcomes and all-cause mortality among the general healthy population. The most comprehensive and recent studies from each cohort were selected to avoid duplication in the meta-analysis.
The Risk of Bias in Non-randomised Studies of Interventions (ROBINS-I) tool was used for risk of bias assessment, covering seven domains of potential bias.
The certainty of evidence was evaluated using the updated Grading ofRecommendations, Assessment, Development, and Evaluations (GRADE) approach, with observational studies initially having a high level of certainty, subject to downgrading or upgrading based on various factors.
In their data analysis, the researchers calculated summary hazard ratios and confidence intervals using a random-effects model. They standardised hazard ratios (SHR) for food portions to maintain consistency.
Measures of inconsistency and between-study variability were also calculated, along with prediction intervals, to estimate the range of future study outcomes.
Some associations were based on pooled risk estimates from multiple cohorts, and in cases where only pooled estimates were available, these were used.
Sensitivity analyses were planned, excluding studies with high bias risk and subgroup analyses. However, due to limited studies, only sensitivity analyses, excluding one study at a time, were conducted.
Publication bias and small study effects were assessed using Egger’s test and funnel plots for studies with sufficient data. All statistical analyses were performed using STATA version 14.1.
In the study, the research team initially identified 1216 studies, which, after removing duplicates and thorough consideration, was narrowed down to 32 studies for inclusion in their analyses.
An additional five relevant studies were found through hand searching, bringing the total number of studies included in the meta-analyses to 37. These were prospective cohort studies, and no randomised controlled trials (RCTs) analyzed as observations were included.
Most of the studies were conducted in the United States of America (USA), with several others from Europe and Asia. Dietary data was primarily collected using validated food frequency questionnaires, and the mean follow-up duration across studies was 19 years. Most cohorts included both men and women, with a few gender-specific exceptions.
Regarding the risk of bias, all studies were deemed to have a moderate chance, except for one with a serious risk due to inadequate adjustment for confounders. The inherent limitations of observational studies, such as the potential for residual confounding and measurement errors in dietary assessment, were noted.
The meta-analyses revealed that for total CVD, replacing processed meat with nuts, legumes, or whole grains, eggs with nuts, and butter with olive oil were all associated with a lower incidence of total CVD. Though these findings had moderate certainty of evidence, the certainty was lower for other potential substitutions.
Regarding single CVD outcomes, moderate certainty of evidence was observed for lower CVD mortality when replacing eggs with nuts and butter with olive oil. For coronary heart disease (CHD) incidence, replacing processed meat with nuts showed a lower risk, but the evidence was low for other substitutions.
For T2D, moderate certainty of evidence indicated a lower risk when replacing red meat with nuts or whole grains or cereals, processed meat with nuts, and poultry with entire grains. Similar associations were observed for replacing eggs with nuts or whole grains.
Regarding all-cause mortality, moderate certainty of evidence supported a reduced risk when substituting red meat, processed meat, and dairy with nuts or legumes; eggs with nuts or legumes; and butter with olive oil. However, the certainty of evidence for other associations was low or very low.
The research included results from individual studies not part of the
meta-analyses, revealing various health impacts of replacing animal-based foods with plant-based alternatives on CVD, CHD, T2D, and all-cause mortality. Sensitivity analyses indicated overall sturdy findings, with some variations in risk estimates when excluding specific studies.
The limited number of studies precluded subgroup analyses and assessment of publication bias. Overall, the study underscores the potential health benefits of dietary shifts from animal to plant-based foods, although the certainty and specificity of the evidence vary.