Background

Red meat collectively refers to beef, goat, lamb, pork, veal, and game meat. Although these meats are sourced from different animals and vary in nutritional composition, they are frequently clustered together under the umbrella term “red meat” in both observational studies and randomized controlled trials assessing the effects of dietary components and/or patterns on cardiometabolic outcomes. Further confounding the effect of clustering all red meat into a singular group, several dietary studies aggregate the already-collective “red meat” with processed meat (meat products that are defined by their preparation, e.g., curing, salting and/or the addition of other ingredients such as nitrates and other preservatives) to the general term “red and processed meat”. Processed meat can be either white meat, e.g. chicken, duck, fish, etc., and/or red meat in origin. Previous studies have indicated that processed red meat is associated with a higher risk for developing cardiovascular disease (CVD) than unprocessed red meat.^1,2 This contributes to confusing dietary advice as the all-encompassing phrase “red and processed meat” does not accurately reflect the evidence for unprocessed red meat or specifically beef, the most frequently consumed type of red meat in the U.S.   

When drawing conclusions from nutrition research, it is essential to consider the quality of the evidence. Systematic reviews and meta-analyses of randomized controlled trials (RCTs) are regarded as the highest quality evidence, as they synthesize data from multiple relevant, and rigorous controlled studies. A systematic review looks at all the available research to help address a clearly defined research question, whereas a meta-analysis analyzes and summarizes the results of the studies included in the systematic review and can help identify inconsistencies in the data.

In contrast, observational studies generally provide lower-quality evidence due to their susceptibility to confounding factors and biases. For example, observational studies suggest associations of higher red meat intake with increased risk of CVD; however, RCTs have not clearly demonstrated a causal link between red meat consumption and CVD risk factors such as low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and systolic and diastolic blood pressures. Despite the lack of clinical evidence, some authoritative bodies and health organizations recommend dietary patterns lower in “red and processed meats”. The 2020-2025 Dietary Guidelines for Americans, the American Heart Association (AHA) and the National Lipid Association all recommend dietary patterns that allow for lean meat intake, which could include lean cuts of red meat. The study authors note, “however, the AHA still penalizes red meat intake, even lean, unprocessed varieties, in the dietary component of ‘Life’s Essential 8’ metric, a metric designed to assess an individual’s or a population’s cardiovascular health.³

Lean, unprocessed beef is often used as a source of red meat in clinical trials evaluating CVD risk factors, and these studies often report little to no effects on CVD risk factors. However, the data from these clinical trials have not been systematically reviewed to assess the specific effect of unprocessed beef on CVD risk factors.

Objective

The objective of this investigation was to perform a systematic review and meta-analysis of results from RCTs evaluating the effects of unprocessed beef intake on select cardiovascular risk factors, namely lipoprotein-related variables, systolic and diastolic blood pressures, and to assess whether the observed effects differ by study quality (defined by rigor, risk of bias, transparency, and reproducibility) and funding source.

Study Design

A search of the literature was conducted using PubMed and CENTRAL databases for RCTs in adults that included diets with unprocessed beef compared to diets with less or no beef.  Trial participants could be generally healthy, or with or at risk for chronic disease with the exception of cancer. Eligible studies were published from database inception to January 2024, when the search was conducted. Data were collected, and the average differences between the group eating higher amounts of beef and the group eating lesser or no beef were calculated and compared.

Bias can influence the findings of meta-analyses that pool results from clinical trials; therefore, several sources of potential bias, including study quality, attrition, publication bias and funding source were evaluated.

Results

• Twenty RCTs met the eligibility criteria and were included in the meta-analysis. The clinical trials included a variety of healthy dietary patterns with unprocessed beef.
• The average amount of beef in the “higher” beef treatments was about 5.7 ounces (161 g/d) or approximately 2 servings/day. Most comparator diets provided 0 ounces of beef, but those that included small amounts of beef averaged about 0.8 ounce (24 g/d) or <1 serving/day. 
• Beef intake did not impact blood pressure or most lipoprotein-related variables, including TC, HDL-C, TG, non-HDL-C, apolipoprotein (apo) A, apo B, and very low-density lipoprotein cholesterol (VLDL-C). 
• Beef consumption had a small, but significant effect on LDL-C corresponding to ~ 2.7 mg/dL higher LDL-C in diets containing more beef compared to low or no beef diets. However, further analysis showed that one study, where subjects followed a very low-calorie diet (600-770 kcal per day), was the primary influence of this result, and when this study was removed, the effect was weakened to a point of insignificance.
• Study quality, as determined by the Cochrane Risk of Bias (ROB) tool, did not have a substantial impact on the results, with the exception of LDL-C, which is likely attributed to one influential study with low risk of bias.
• Publication bias refers to the selective publication of research studies based on their results. No publication bias for any outcomes were detected.
• Attrition rates, or the consideration of the completeness of data and how missing data are handled, did not impact the results for any outcomes.

• No bias based on funding source was reported. In fact, 71% of studies funded by the beef industry had a low risk of bias compared to 40% of studies not funded by the beef industry.

Unprocessed beef contains more cholesterol-lowering or neutral fatty acids than cholesterol-raising fatty acids, supporting the finding that daily unprocessed beef intake did not significantly affect most blood lipids, apolipoproteins, or blood pressures compared to diets with little to no beef.

Study Implications

• High-quality research shows eating an average of up to 5.7 ounces of unprocessed beef per day has minimal to no impact on many cardiovascular disease risk factors. Beef can be enjoyed as a high-quality, nutrient-dense protein in heart-healthy dietary patterns.
• In addition, as a source of high-quality protein and bioavailable iron, zinc, and other nutrients, eating beef in a healthy dietary pattern can help improve nutrient profiles without significantly affecting blood lipids or blood pressure.
• This manuscript contributes to the existing body of evidence evaluating the impact of beef intake on markers of cardiovascular health, including blood lipids and blood pressure, independent of other red meat.