Health effects associated with vegetable consumption: a Burden of Proof study

Abstract

Previous research suggests a protective effect of vegetable consumption against chronic disease, but the quality of evidence underlying those findings remains uncertain. We applied a Bayesian meta-regression tool to estimate the mean risk function and quantify the quality of evidence for associations between vegetable consumption and ischemic heart disease (IHD), ischemic stroke, hemorrhagic stroke, type 2 diabetes and esophageal cancer. Increasing from no vegetable consumption to the theoretical minimum risk exposure level (306–372 g daily) was associated with a 23.2% decline (95% uncertainty interval, including between-study heterogeneity: 16.4–29.4) in ischemic stroke risk; a 22.9% (13.6–31.3) decline in IHD risk; a 15.9% (1.7–28.1) decline in hemorrhagic stroke risk; a 28.5% (−0.02–51.4) decline in esophageal cancer risk; and a 26.1% (−3.6–48.3) decline in type 2 diabetes risk. We found statistically significant protective effects of vegetable consumption for ischemic stroke (three stars), IHD (two stars), hemorrhagic stroke (two stars) and esophageal cancer (two stars). Including between-study heterogeneity, we did not detect a significant association with type 2 diabetes, corresponding to a one-star rating. Although current evidence supports increased efforts and policies to promote vegetable consumption, remaining uncertainties suggest the need for continued research.

The Burden of Proof studies: assessing the evidence of risk

“…Figure 3 summarizes the cohort data on vegetable consumption and ischemic heart disease using 78 observations from 17 cohort studies 27 . The relationship is not log-linear.…”

“…See Supplementary Tables 7 – 10 for detailed information on the included data sources for each example risk–outcome pair. For a full description of how each of the four selected risk–outcome pairs were defined and measured, how data inputs were identified and assessed for eligibility, the summary results from input studies and other information on conducting systematic reviews for each risk, see Dai et al 25 , Razo et al 26 , Stanaway et al 27 , and Lescinsky et al 28 . Detailed PRISMA checklists are also included in the supplementary information of each of these articles.…”

Dietary patterns and risk for gastric cancer: A case-control study in residents of the Huaihe River Basin, China

“…Fourth, the data on total energy intake were not available in this study and it was not adjusted as a confounder. Fifth, confounding would distort the strength of the association ( 33 ). Although some potential confounders in this analysis were adjusted for, it was likely that some residual confounding remained due to imperfect statistical adjustment, imperfect confounder measurement, and the existence of confounders that were unknown, unmeasured or otherwise unadjusted for ( 33 ).…”

“…Fifth, confounding would distort the strength of the association ( 33 ). Although some potential confounders in this analysis were adjusted for, it was likely that some residual confounding remained due to imperfect statistical adjustment, imperfect confounder measurement, and the existence of confounders that were unknown, unmeasured or otherwise unadjusted for ( 33 ). Sixth, there existed the missing value of H. pylori in our study, which was a great contributor to increase the risk of gastric cancer.…”

Studies linking diet with health must get a whole lot better

“…It finds no relationship in studies that explore whether eating unprocessed red meat leads to two kinds of strokes. There is stronger, but not overwhelming, evidence that eating vegetables reduces the risk of strokes and ischaemic heart disease 6 .…”