Eating soy products linked to lower cancer risk, study finds

By Priyanjana Pramanik, MSc.Apr 1 2024Reviewed by Benedette Cuffari, M.Sc.

In a recent review published in Nutrients, researchers discuss possible associations between the consumption of soy products and the risk of developing cancer.

Study: Soy product consumption and the risk of cancer: a systematic review and meta-analysis of observational studies. Image Credit: naito29 / Shutterstock.com

Background

Cancer rates continue to rise globally, with breast, lung, colorectal, prostate, and stomach cancers leading in terms of both new cases and deaths. Researchers have observed variations in cancer prevalence between Asia and the West, which may be attributed to different dietary habits, particularly soy product consumption.

Soy products, which are abundant in Asia, are rich in compounds like isoflavones, phytosterols, and dietary fiber, all of which may mitigate cancer risk. However, research suggests these effects vary with soy products and cancer types.

About the study

The current study aimed to systematically review the relationship between various soy products and the risk of cancer through a detailed dose-response meta-analysis. To this end, 52 studies were included in the review, 35 and 17 of which were case-control and cohort studies, which led to a final total of 44,932 cases and 861,372 participants.

Over 80% of the reviewed studies were conducted in Asia, particularly Japan, China, Korea, and Singapore. Comparatively, 15% of studies were conducted in the United States, and two were performed in Europe.

Quality assessment revealed case-control studies averaging a score of 6.7, while cohort studies had an average score of 7.2, thus indicating high quality. Adjustments for age were universal, with most studies also considering education level, smoking, drinking, energy intake, and body mass index (BMI) values.

Consumption of all soy products

A sample of 28 studies with 24,090 cases and 553,282 participants was used to assess the association between the total consumption of soy products and the risk of cancer. High soy product intake correlated with a 31% reduced risk of cancer, particularly in the subsample of case-control studies, with a 24% risk reduction in women but not men.

Notable risk reductions were observed in gynecological cancers, including ovarian cancers, as well as cancers affecting the gastrointestinal and upper aerodigestive tract, prostate, and lungs. Geographic variations were evident, with lower cancer risks associated with soy consumption in Korea, Singapore, Europe, and China.

The dose-response analysis indicated non-linear relationships, with increased soy consumption associated with a reduced cancer risk.

Tofu consumption

A sample of seven cohort and 19 case-control studies, which comprised 18,729 cases and 312,770 participants, explored the impact of tofu consumption on cancer risk. To this end, high tofu intake significantly reduced cancer risk by 22%, with consistent effects observed in both males and females.

This reduction was more pronounced in the subsample of case-control studies. Consumption of tofu correlated with lower risks of gynecological and gastrointestinal cancers, particularly those affecting the stomach, breast, ovaries, and endometrium.

However, no significant effects were observed for cancers of the liver, prostate, and lungs, non-Hodgkin lymphoma, or upper aerodigestive tract cancers. Geographic differences were evident, with significant inverse associations in Korea, China, and the U.S., but not in Japan or Europe.

Moreover, the dose-response analysis revealed a non-linear relationship, with increased tofu consumption associated with a reduced cancer risk, particularly with daily increments of 100 grams or more.

Soymilk consumption

A sample of 11 studies comprising 177,626 participants and 8,269 cases analyzed the relationship between soymilk consumption and cancer risk. Overall, high soymilk intake was associated with a 25% reduced risk of cancer, particularly in the case-control studies.

Significant inverse associations were identified for gastrointestinal, upper aerodigestive, and ovarian cancers. However, no significant effects were observed for breast, endometrial, lung, or liver cancers.

The impact of soymilk consumption varied geographically, with inverse associations observed in China and Korea but not in Singapore, Europe, or the U.S. Conversely, a positive correlation was observed in Japan.

The dose-response analysis revealed a non-linear relationship: increased soymilk consumption is associated with reduced cancer risk, particularly for those who consume 30 grams or more of soymilk daily.

Other soy products

A meta-analysis was also performed on studies that investigated various soy products, including miso soup, non-fermented and fermented products, soy paste, and natto. While no significant associations with reduced total cancer risk were observed overall, subgroup analyses revealed nuanced findings.

The subsample of case-control studies suggested that high natto consumption might reduce total cancer risk. Subgroup analyses by cancer type indicated potential risk reduction for gastric cancer with non-fermented products, whereas a potentially reduced risk of breast cancer was associated with soy paste.

However, increased intake of fermented products in China was associated with a greater cancer risk. No significant differences in cancer risk between genders were found. The dose-response analysis suggested a linear relationship between soy product consumption and cancer risk; however, no significant associations were reported.

Conclusions

Higher consumption of total soy foods, tofu, and soymilk was associated with a reduced risk of cancer, particularly gastrointestinal and gynecological cancers. However, evidence regarding other soy products is insufficient, thus necessitating the need for additional well-designed prospective cohort studies.