Table 2. Effects of soy products on PCA incidence.

Subgroup analysis			No. of studies	OR	95% CI	p-value	Heterogeneity (I2) (%)
Soy products			20	0.94	0.91–0.97	<0.001	40.3
Cohort study			9	0.98	0.95–1.00	0.056	19.0
Case-control study			11	0.94	0.94–0.97	<0.001	40.3
Soy products consumption
	0–50 g/day		11	0.99	0.97–1.00	0.143	0.0
	50–100 g/day		12	0.98	0.93–1.04	0.586	41.7
	100–150 g/day		11	0.93	0.87–0.99	0.018	35.5
	>150 g/day		6	0.91	0.82–1.01	0.078	64.1
Soy products consumption frequency
	<1 time/day		3	0.94	0.84–1.05	0.254	0.0
	≥1 time/day		6	0.80	0.65–0.99	0.038	30.5
Racial demographics
	African Americans		2	0.89	0.81–0.97	0.006	55.5
	Japanese		2	0.99	0.93–1.05	0.655	0.0
	Whites		2	0.96	0.90–1.01	0.133	0.0
	Latinos		2	0.93	0.87–1.00	0.036	8.9
	Chinese		2	0.90	0.79–1.04	0.155	0.0
Prostate cancer stage
	Non-localized or high-grade		5	0.96	0.91–1.01	0.085	54.0
	Localized or low grade		3	0.94	0.90–0.97	<0.001	19.9
Soy products subtypes
	Fermented soy products		7	1.10	0.98–1.22	0.096	10.7
		Natto	2	0.98	0.77–1.24	0.837	15.8
		Miso	5	1.15	1.00–1.33	0.047	16.9
	Non-fermented soy products		18a	0.93	0.90–0.96	<0.001	44.3
		Tofu	10	0.93	0.85–1.01	0.099	28.8
		Legumes	8	0.95	0.92–0.98	0.001	45.5
		Soy milk	10	0.84	0.75–0.93	0.001	47.4

PCA, prostate cancer; OR, odds ratio; CI, confidence interval.

^a:Some studies have also explored the effects of soy milk, tofu, and soybeans on prostate cancer. There are overlapping groups between the studies, so the total number is less than the sum of the studies in the following three subgroups.