Legume and soy intake and risk of type 2 diabetes: a systematic review and meta-analysis of prospective cohort studies

Am J Clin Nutr. 2020 Mar 1;111(3):677-688. doi: 10.1093/ajcn/nqz338.


Background: Previous findings on the associations of legume and soy intake with the risk of type 2 diabetes are conflicting.

Objective: We aimed to summarize the longitudinal associations between legume and soy intake and risk of type 2 diabetes.

Methods: We searched for relevant prospective cohort studies in PubMed, EMBASE, and Ovid up to August 2019. Study-specific, multivariable-adjusted RRs and 95% CIs were pooled by random-effects models.

Results: We identified 15 unique cohorts including 565,810 individuals and 32,093 incident cases. The summary RRs (95% CIs) of incident type 2 diabetes were 0.95 (0.79, 1.14; NS) for total legumes, 0.83 (0.68, 1.01; NS) for total soy, 0.89 (0.71, 1.11; NS) for soy milk, 0.92 (0.84, 0.99) for tofu, 0.84 (0.75, 0.95) for soy protein, and 0.88 (0.81, 0.96) for soy isoflavones, respectively. High heterogeneity was found for total legumes (I2 = 84.8%), total soy (I2 = 90.8%), and soy milk (I2 = 91.7%). Potential sources of heterogeneity were not evident for total legumes or soy milk, whereas for total soy, geographic location (Asia, United States; P = 0.04) and study quality (high, moderate, or low; P = 0.02) significantly predicted heterogeneity. In dose-response analysis, significant linear inverse associations were observed for tofu, soy protein, and soy isoflavones (all P < 0.05). Overall quality of evidence was rated as moderate for total legumes and low for total soy and soy subtypes.

Conclusions: Dietary intakes of tofu, soy protein, and soy isoflavones, but not total legumes or total soy, are inversely associated with incident type 2 diabetes. Our findings support recommendations to increase intakes of certain soy products for the prevention of type 2 diabetes. However, the overall quality of evidence was low and more high-quality evidence from prospective studies is needed. This trial was registered as PROSPERO CRD42019126403 (https://www.crd.york.ac.uk/PROSPERO).

Keywords: cohort; legume; meta-analysis; soy; type 2 diabetes.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't
  • Systematic Review

MeSH terms

  • Adult
  • Aged
  • Diabetes Mellitus, Type 2 / epidemiology*
  • Diabetes Mellitus, Type 2 / metabolism*
  • Diabetes Mellitus, Type 2 / prevention & control
  • Fabaceae / metabolism*
  • Female
  • Glycine max / metabolism*
  • Humans
  • Male
  • Middle Aged
  • Prospective Studies
  • Soy Foods / analysis