Zeraatkar D, Johnston BC, Bartoszko J, et al. Effect of Lower Versus Higher Red Meat Intake on Cardiometabolic and Cancer Outcomes: A Systematic Review of Randomized Trials. Ann Intern Med. 2019 Oct 1. pii: 2752326. doi: 10.7326/M19-0622. (Systematic review)

Background: Few randomized trials have evaluated the effect of reducing red meat intake on clinically important outcomes.

Purpose: To summarize the effect of lower versus higher red meat intake on the incidence of cardiometabolic and cancer outcomes in adults.

Data Sources: EMBASE, CENTRAL, CINAHL, Web of Science, and ProQuest from inception to July 2018 and MEDLINE from inception to April 2019, without language restrictions.

Study Selection: Randomized trials (published in any language) comparing diets lower in red meat with diets higher in red meat that differed by a gradient of at least 1 serving per week for 6 months or more.

Data Extraction: Teams of 2 reviewers independently extracted data and assessed the risk of bias and the certainty of the evidence.

Data Synthesis: Of 12 eligible trials, a single trial enrolling 48 835 women provided the most credible, though still low-certainty, evidence that diets lower in red meat may have little or no effect on all-cause mortality (hazard ratio [HR], 0.99 [95% CI, 0.95 to 1.03], cardiovascular mortality (HR, 0.98 [CI, 0.91 to 1.06]), and cardiovascular disease (HR, 0.99 [CI, 0.94 to 1.05]). That trial also provided low- to very-low-certainty evidence that diets lower in red meat may have little or no effect on total cancer mortality (HR, 0.95 [CI, 0.89 to 1.01]) and the incidence of cancer, including colorectal cancer (HR, 1.04 [CI, 0.90 to 1.20]) and breast cancer (HR, 0.97 [0.90 to 1.04]).

Limitations: There were few trials, most addressing only surrogate outcomes, with heterogeneous comparators and small gradients in red meat consumption between lower versus higher intake groups.

Conclusion: Low- to very-low-certainty evidence suggests that diets restricted in red meat may have little or no effect on major cardiometabolic outcomes and cancer mortality and incidence.

Primary Funding Source: None (PROSPERO: CRD42017074074).

Discipline Area Score
Family Medicine (FM)/General Practice (GP) 6 / 7
General Internal Medicine-Primary Care(US) 6 / 7
Public Health 5 / 7
Internal Medicine Coming Soon...
Comments from MORE raters

Family Medicine (FM)/General Practice (GP) rater

The quality of evidence makes the findings of the study unhelpful.

Internal Medicine rater

The lack of evidence is surprising.

Public Health rater

This is a difficult area of research given that only observational data are available and only small-sized high-quality trials are available. Combination of trials with very different patient populations, follow-up durations, and methodologies is problematic. In 7 of 12 trials, the difference in meat serving size consumption was not reported and excludes about 670 participants. The authors state that several trials had different biases. The authors decision to put the Lyons data as a supplement and talk about only WHI data itself may be a form of bias. This article got a lot of traction despite its inherent weaknesses. Physicians use common sense to decide when a dietary modification is useful for a given patient and follow up with appropriate evaluations.

Public Health rater

The evidence quality seems quite simply too poor to draw meaningful inferences.

Public Health rater

This systematic review of RCTs is well done. There are few large trials, so the data are dominated by the WHI. Overall, little support for recommendations on meat in the diet. These data are different than what has been seen in observational trials, so the two study types need to reconciled. There may be other reasons to limit meat intake besides direct health effects (e.g., impact on climate).

Public Health rater

This paper is remarkable not for its conclusion but because it illustrates two important concepts: 1. Not all questions can be answered using the same methodology, and; 2. The absence of evidence is not the same as the absence of an effect. The authors conducted a systematic review of RCTs on a topic where RCTs are known to be very expensive, very difficult to do, and rare. To nobody's surprise, they found little evidence (1 study) and rehashed these results. Their conclusion: not a lot of evidence. This article does not advance our knowledge of nutrition but it raises a red flag to readers.
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