Soy Product Consumption and the Risk of Cancer: A Systematic Review and Meta-Analysis of Observational Studies

Abstract

Background: The association between soy product consumption and cancer risk varies among studies. Therefore, this comprehensive meta-analysis of observational studies examines the association between soy product consumption and total cancer risk.

Methods: This study was conducted following the PRISMA guidelines. Up to October 2023, all eligible published studies were searched through PubMed and Web of Science databases.

Results: A total of 52 studies on soy product consumption were included in this meta-analysis (17 cohort studies and 35 case-control studies). High consumption of total soy products (RR: 0.69; 95% CI: 0.60, 0.80), tofu (RR: 0.78; 95% CI: 0.70, 0.86), and soymilk (RR: 0.75; 95% CI: 0.60, 0.93) were associated with reduced total cancer risk. No association was found between high consumption of fermented soy products (RR: 1.18; 95% CI: 0.95, 1.47), non-fermented soy products (RR: 0.95; 95% CI: 0.77, 1.18), soy paste (RR: 1.00; 95% CI: 0.88, 1.14), miso soup (RR: 0.99; 95% CI: 0.87, 1.12), or natto (RR: 0.96; 95% CI: 0.82, 1.11) and cancer risk. A 54 g per day increment of total soy products reduced cancer risk by 11%, a 61 g per day increment of tofu reduced cancer risk by 12%, and a 23 g per day increment of soymilk reduced cancer risk by 28%, while none of the other soy products were associated with cancer risk.

Conclusion: Our findings suggest that high total soy product consumption, especially soymilk and tofu, is associated with lower cancer risk. More prospective cohort studies are still needed to confirm the causal relationship between soy product consumption and cancer risk.

Keywords: cancer; dose–response; meta-analysis; observational study; soy product.

Figure 1

Flow diagram of the literature search and study selection.

Figure 2

Forest plot of cancer risk for the highest versus lowest categories of soy product consumption: (A) Forest plot of cancer risk for the highest versus lowest categories of total soy product consumption. Data is from references [14,15,16,18,19,20,35,36,37,39,40,41,45,47,60,61,63,64,66,69,70,72,73,74,75,80,82,83]. (B) Forest plot of cancer risk for the highest versus lowest categories of tofu consumption. Data is from references [12,13,14,15,16,17,18,20,38,44,46,56,57,60,61,62,65,67,68,71,72,76,77,79,81,83]. (C) Forest plot of cancer risk for the highest versus lowest categories of soymilk consumption. Data is from references [15,18,20,56,61,67,71,72,73,78,83].

Figure 3

Dose–response analysis of soy product and the risk of cancer (A) Dose–response study of total soy product and cancer risk. (B) Dose–response analysis of total soy product and cancer risk, with reference dose as cut-off point. (C) Dose–response analysis of tofu and the risk of cancer. (D) Dose–response analysis of tofu and cancer risk, with reference dose as cut-off point. (E) Dose–response analysis of soymilk and the risk of cancer. (F) Dose–response analysis of total soymilk and the risk of cancer, with reference dose as cut-off point. Relative risks are indicated by solid lines, the blue-shaded regions indicate the 95% confidence intervals, and purple vertical line indicate the reference point.

Figure 4

Forest plot of cancer risk for the highest versus lowest categories of soy product consumption: (A) Forest plot of cancer risk for the highest versus lowest categories of soy paste consumption. Data is from references [5,14,15,17,18,20,37,43,63,67,71,83]. (B) Forest plot of cancer risk for the highest versus lowest categories of miso soup consumption. Data is from references [16,34,35,36,38,44,56,59,62,76]. (C) Forest plot of cancer risk for the highest versus lowest categories of natto consumption. Data is from references [16,20,37,38,44,83]. (D) Forest plot of cancer risk for the highest versus lowest categories of fermented soy product consumption. Data is from references [18,19,20,37,42,58,83]. (E) Forest plot of cancer risk for the highest versus lowest categories of non-fermented soy product consumption. Data is from references [18,19,20,37,63,83].

Figure 5

Dose–response analysis of soy product and the risk of cancer: (A) Dose–response study of soy paste and cancer risk. (B) Dose–response analysis of natto and the risk of cancer. (C) Dose–response analysis of miso soup and the risk of cancer. (D) Dose–response analysis of fermented soy product and the risk of cancer. (E) Dose–response analysis of non-fermented soy product and the risk of cancer. Relative risks are indicated by solid lines, and the blue-shaded regions indicate the 95% confidence intervals.