Legume intakes on cardiometabolic profile and gut microbiome function: systematic review and meta-analyses of randomised controlled trials

Background: Legumes are widely considered one of the most beneficial food groups to consume. They are high in fibre and plant-based protein as well as naturally low in sodium, saturated fats, and sugars. However, legumes do not feature prominently in the modern diet, and previous evidence syntheses show inconsistent results on cardiometabolic risk profile when increasing legume intakes. This review examines the impact of legume intake on cardiometabolic profile and gut microbiome.

Methods: EMBASE, OVID Medline, and the Cochrane Central Register of Controlled Trials were searched up to 15 May 2024 with checking of relevant reference lists and bibliographies. Relevant data were extracted into pre-tested forms and risk of bias was assessed with Cochrane RoB2. Searches, screening, and risk of bias assessment were done independently by two reviewers. We have considered trials where legumes were provided to adults, with and without pre-existing conditions (i.e. type 2 diabetes, heart disease or dyslipidaemia), in randomised controlled trials of at least six weeks duration on cardiometabolic risk factors and gut microbiome outcomes. Trial data were pooled using random effects models. Prespecified regression analyses were then performed to identify the factors influencing pooled results. Certainty of evidence was assessed with GRADE.

Results: We identified 30 papers of 24 trials with 33 eligible comparisons where legumes (daily average 86 g (range 2-251)) were provided to 1,938 participants. No eligible studies reported on microbiome outcomes. There was moderate certainty evidence that higher legume intakes improved total cholesterol (mean difference (MD) -0.23mmol/L, 95%CI -0.33 to -0.13), LDL cholesterol (MD -0.16mmol/L (-0.24 to -0.08)), and fasting blood glucose (MD -0.18mmol/L (-0.30 to -0.06)). The majority of trial comparisons (70%) provided an isoenergetic control food. Pooled results were influenced by underlying differences between trials such as type and format of legumes provided, but not consistently across multiple outcomes.

Conclusions: Increasing legume intakes improved some blood lipid and glucose parameters, but not all. Isoenergetic comparisons in trials may obscure changes in cardiometabolic risk factors due to greater satiation or reduced intake, and no trials greater than six weeks duration were identified to consider the microbiome-mediated health effects with greater legume intakes. Future trials in these areas are necessary.

Trial registration: Prospero ID CRD42023456953.