Soy, Soy Isoflavones, and Protein Intake in Relation to Mortality from All Causes, Cancers, and Cardiovascular Diseases: A Systematic Review and Dose–Response Meta-Analysis of Prospective Cohort Studies



      We conducted a systematic review and dose–response meta-analysis of prospective studies to summarize findings on the associations between intakes of soy, soy isoflavones, and soy protein and risk of mortality from all causes, cancers, and cardiovascular diseases.


      Online databases were systematically searched to identify relevant articles published earlier than May 2018. We applied restricted cubic splines using random-effects analysis to assess dose–response associations. Between-study heterogeneity was assessed by I
      • Ahn-Jarvis J.
      • Clinton S.K.
      • Riedl K.M.
      • Vodovotz Y.
      • Schwartz S.J.
      Impact of food matrix on isoflavone metabolism and cardiovascular biomarkers in adults with hypercholesterolemia.
      value and Cochrane Q test. Potential publication bias was assessed by visual inspection of funnel plots and Begg regression test.


      In total, 23 prospective studies with an overall sample size of 330,826 participants were included in the current systematic review and the meta-analysis. Soy/soy products consumption was inversely associated with deaths from cancers (pooled relative risk 0.88, 95% CI 0.79 to 0.99; P=0.03; I2=47.1%, 95% CI 0.0% to 75.4%) and cardiovascular diseases (pooled effect size: 0.85, 95% CI 0.72 to 0.99; P=0.04; I2=50.0%, 95% CI 0.0% to 77.6%). Such significant associations were also observed for all-cause mortality in some subgroups of the included studies, particularly those with higher quality. In addition, higher intake of soy was associated with decreased risk of mortality from gastric, colorectal, and lung cancers as well as ischemic cardiovascular diseases. Participants in the highest category of dietary soy isoflavones intake had a 10% lower risk of all-cause mortality compared with those in the lowest category. We also found that a 10-mg/day increase in intake of soy isoflavones was associated with 7% and 9% decreased risk of mortality from all cancers and also breast cancer respectively. Furthermore, a 12% reduction in breast cancer death was indicated for each 5-g/day increase in consumption of soy protein. However, intake of soy protein was not significantly associated with all-cause and cardiovascular diseases mortality.


      Soy and its isoflavones may favorably influence risk of mortality. In addition, soy protein intake was associated with a decreased risk in the mortality of breast cancer. Our findings may support the current recommendations to increase intake of soy for greater longevity.


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      S. M. Nachvak is an associate professor of nutrition sciences, Department of Nutritional Sciences, Research Center for Environmental Determinants of Health (RCEDH) and Student of Research Committee, Health Institute, School of Nutritional Sciences and Food Technology, Kermanshah University of Medical Sciences, Kermanshah, Iran.


      S. Moradi is an academic researcher, Department of Nutritional Sciences, Research Center for Environmental Determinants of Health (RCEDH) and Student of Research Committee, Health Institute, School of Nutritional Sciences and Food Technology, Kermanshah University of Medical Sciences, Kermanshah, Iran.


      J. Anjom-shoae is an MSc student of nutrition sciences, Students’ Scientific Research Center and Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran.


      J. Rahmani is a PhD student of nutrition sciences, Department of Community Nutrition, Faculty of Nutrition and Food Technology, National Nutrition and Food Technology Research Institute, Student Research Committee, Shahid Beheshti University of Medical Sciences, Tehran, Iran.


      M. Nasiri is a PhD student of nursing, Student Research Committee and Department of Operating Room Nursing, School of Nursing and Midwifery, Shiraz University of Medical Sciences, Shiraz, Iran.


      V. Maleki is a PhD student of nutrition sciences, Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran.


      O. Sadeghi is an academic researcher, Department of Nutritional Sciences, RCEDH and Student of Research Committee, Health Institute, School of Nutritional Sciences and Food Technology, Kermanshah University of Medical Sciences, Kermanshah, Iran; and a PhD student of nutrition, Students' Scientific Research Center and Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran.