Soybean paste is not recommended for breast cancer
Soybean paste is a type of fermented bean paste widely used in Asian cuisine. Soybean paste normally is salty and may also be spicy. The soybeans may be roasted or aged before being ground to make the paste and various other ingredients such as wheat flour, sugar or hot pepper paste may be incorporated into the paste. The conditions of fermentation and microflora used in production also affect the flavor. Soybean paste is used as a condiment to flavor dishes such as stir-fries and soups. Miso is a fermented soybean paste widely used in Japan as a soup base or for seasoning. This web page focuses on soybean paste; tofu, soybean oil, soy protein isolate and soybeans are covered in separate web pages. We attempt to untangle the conflicting findings regarding breast cancer risk and soybean isoflavones in the genistein and daidzein web page.Cancer-related effects of consuming soybean paste
Soybean paste contains higher levels of genistein and daidzein than soybeans and extracts of soybean paste have been shown to have antimutagenic activities. However, whereas some Asian population studies have found reductions in breast cancer risk associated with consumption of other soy products such as tofu, such a reduction in risk usually is not found for soybean paste. On the other hand, Asian studies have consistently found that frequent consumption of soybean paste is associated with higher risk of gastric cancer. Stomach cancer is the most prevalent cancer in Korea and it is also common in other parts of Asia compared to the U.S. Some observers have suggested that the association between soybean paste and gastric cancer is mainly due to its high salt content.
There is some evidence that breast cancer survivors are at increased risk of developing stomach cancer and lobular breast cancer survivors in particular are vulnerable to gastric metastases. However, the effect of consuming soybean paste are likely to be minimal if not part of a high-salt diet; it may be that regularly eating small amounts of soybean paste (including miso) in a diet that contains few other traditional fermented, salted or pickled foods might have little carcinogenic effect compared to eating it as part of a traditional Asian diet. Based on the available evidence, soybean paste should not be considered protective against breast cancer and consuming much of it could heighten gastric cancer risk.
Additional comments
Soybean paste was found to be a meaningful source of Aflatoxin B1 in the Koran diet in one study. Aflatoxins, which are mutagenic, carcinogenic and teratogenic and cause immuno-suppression in humans, are produced by molds. Aflatoxin B1 has been shown to cause liver cancer, especially in hepatitis B-positive individuals. Buyers of soybean paste should be aware of its source and assure themselves of its safety and quality.
Selected studies
Association between the intake of soy foods and risk of breast cancer in Korean women American Association for Cancer Research (AACR) Meeting, April 2008The present Korean case-control study was designed to examine the associations between consumption of soy foods and breast cancer risk. A total of 1.399 newly-diagnosed breast cancer cases were recruited in the period 1998 to 2004 from a Seoul university hospital. The study also included 938 cancer-free controls selected from seven different clinical departments at the same time in the same hospital. The women were interviewed in detail concerning their diets and life-style factors. Multivariate odds ratios (mOR) and 95% confidence intervals (CI) concerning daily intakes of soybean, tofu, and soybean paste were calculated using unconditional logistic regression. Adjustment was made for known risk factors, including age, education, family history of breast cancer, history of benign breast diseases, smoking, alcohol intake, height, body mass index, number of full term deliveries, age at menarche, menopausal status, and use of hormone replacement therapy. Compared to those in the lowest fifth (Q1), women in the highest quintile (Q5) of soybean intake had lower odds of having the breast cancer (mOR = 0.70, 95% CI = 0.54-0.89). High tofu consumption also was found to have an inverse association with risk of breast cancer (Q5 vs. Q1; mOR = 0.67, 95% CI = 0.51-0.89). On the other hand, high soybean paste consumption was not found to have a significant association with breast cancer (Q5 vs. Q1; mOR = 0.85, 95% CI = 0.63-1.14). The association between soybean consumption and breast cancer was found to be stronger in postmenopausal women (mOR = 0.60, 95% CI = 0.39-0.91) than in premenopausal women (mOR = 0.76, 95% CI = 0.56-1.04). Conversely, the association between tofu intake and breast cancer risk also was found to be stronger in premenopausal women (mOR = 0.62, 95% CI=0.44-0.87) than in postmenopausal women (mOR = 0.78, 95% CI = 0.45-1.26). The authors conclude that high intakes of soy bean and tofu, but not soybean paste, have inverse associations with breast cancer risk.
Natural Occurrence of Aflatoxin B1 in Marketed Foods and Risk Estimates of Dietary Exposure in Koreans Journal of Food Protection, December 2007
The present study determined the natural occurrence of Aflatoxin B1 in food and estimated the excess risk for liver cancer through exposure to Aflatoxin B1 to Koreans posed by food consumption. 694 food samples from six different regions of South Korea were analyzed for their Aflatoxin B1 content. Thirty-two samples were found to be contaminated with Aflatoxin B1. The level of contamination in 28 of the 32 food products was below 10 μg kg−1, which is the upper legal limit in Korea. From data on typical daily food consumption, the exposure to Aflatoxin B1 was estimated. The major contributors to the dietary intake of Aflatoxin B1 were soybean paste and soy sauce, which composed 91% of the total exposure to Aflatoxin B1. The additional risk of liver cancer for those exposed to Aflatoxin B1 through food was estimated to be 5.78 × 10−6 for hepatitis B-negative individuals and 1.48 × 10−4 for hepatitis B-positive individuals.
Diet and cancer of the stomach: A case-control study in China International Journal of Cancer, July 2006
The present case-control study was designed to evaluate the association between single food items and stomach cancer in the Heilongjiang area of China. The study included 241 patients with histologically verified stomach cancer and an equivalent number of controls (with non-cancer-related diseases) who were matched by age, sex and area of residence. The participants were interviewed during a two-year period regarding their economic status, occupation, history of smoking and of drinking, diet and dietary habits and medical history. Detailed data concerning the average frequency and quantity of intake of single food items were also obtained by the same interviewer. An inverse association between the intake of vegetables and stomach cancer was found. In particular, Chinese cabbage was found to play an important role in reducing the risk of developing stomach cancer. On the other hand, frequent consumption of potatoes and of salted and fermented soybean paste appeared to be high-risk factors.
Kimchi and soybean pastes are risk factors of gastric cancer World Journal of Gastroenterology, June 2005
Stomach cancer is the most prevalent cancer in Korea. The current study was designed to investigate the relationship between consumption of kimchi, soybean paste, fresh vegetables, nonfermented alliums, nonfermented seafood, nonfermented soybean foods, and the genetic polymorphisms of some metabolic enzymes on the risk of gastric cancer in Koreans. 421 gastric cancer patients and 632 age and sex-matched controls completed a food intake questionnaire. Polymorphisms of cytochrome P450 1A1 (CYP1A1), cytochrome P450 2E1 (CYP2E1), glutathione S-transferase mu 1 (GSTM1), glutathione S-transferase theta 1 (GSTT1) and aldehyde dehydrogenase 2 (ALDH2) were evaluated. The study found a lower risk of gastric cancer among people with high consumption of unfermented alliums and unfermented seafood. On the other hand, consumption of kimchi and soybean paste was associated with increased risk of gastric cancer. People with the CYP1A1 Ile/Val or Val/Val genotype demonstrated a significant increased risk for gastric cancer. The authors conclude that Kimchi, soybean paste, and the CYP1A1 Ile/Val or Val/Val are risk factors, whereas unfermented seafood and alliums are protective factors against gastric cancer in Koreans. Salt or some other chemicals contained in kimchi and soybean pastes, which are increased by fermentation, likely play important roles in the carcinogenesis of stomach cancer.
Determination of ethyl carbamate in some fermented Korean foods and beverages Food Additives and Contaminants, June 2000
Ethyl carbamate, found primarily in fermented foods and beverages, has been associated with cancer in several studies. Fermented foods are important in the Korean diet The present study was designed to determine ethyl carbamate concentrations in some staple food items and estimate the daily intake for the Korean population. Ethyl carbamate was measured in commercial samples of kimchi, soy sauce, vinegar, soybean paste, and alcoholic beverages, as well as homemade soy sauce and kimchi. The maximum ethyl carbamate concentrations observed were 73 μg/kg in soy sauce, 16.2 μg/kg in kimchi, 15.4 μ/l in Korean traditional alcoholic beverages, 7.9 μg/kg in soybean paste and 2.5 μg/l in vinegar. Combining these values with average daily food intake data, the authors estimated that the maximum daily exposure of the Korean population to ethyl carbamate is 2.8 μg/day, which is a significant amount considering that the safe dose derived by animal experiment ranges between 1.2 and 4.8 μg/day.
Lifestyle and anti-Helicobacter pylori immunoglobulin G antibody among outpatients Japanese Journal of Cancer Research, November 1997
The present hospital-based case-control study was designed to investigate the association between diet and Helicobacter pylori (H. pylori) infection. Eradication of H. pylori is thought to be a preventive measure against stomach cancer. The study included 140 cases that were H. pylori antibody-positive (75 males and 65 females) and 52 antibody-negative controls (22 males and 30 females). All study participants were outpatients who had undergone gastroscopy at Aichi Cancer Center Hospital between February 1995 and February 1997. Lifestyle data was collected on the first visit (baseline). A strong association was observed between H. pylori infection and smoking among males: age-adjusted odds ratio (OR) = 7.85, 95% confidence interval (CI) = 2.03-30.4. Rice breakfast (OR = 3.74; 95% CI = 1.30-10.8) and soybean paste soup (every day vs. occasionally, OR = 5.24; 95% CI, =1.80-15.2) were also found to be associated with H. pylori antibody positivity in men, but not in women. In women, pickled Chinese cabbage (at least once per week vs. three times per month or fewer, OR = 2.82; 95% CI = 1.06-7.48) and lettuce (at least once per week vs. three times per month or fewer, OR = 2.90; 95% CI = 1.09-7.76) were significantly associated with antibody positivity. The authors comment that smoking may work as a cofactor disturbing incidental eradication of H. pylori by antibacterial agents administered for other reasons.
Quantification of genistein and genistin in soybeans and soybean products Food and Chemical Toxicology, May 1996
The current study was designed to estimate the levels of genistein and its β-glucoside conjugate, genistin, in soybeans and related products and Japanese levels of consumption. The isoflavones genistein and genistin may have some role as a chemopreventive agent against cancer. The genistein and genistin contents of soybeans, soy nuts and soy powder were found to be in the range of 4.6-18.2 and 200.6-968.1 μg/g food, respectively. The genistein and genistin contents of soy milk and tofu (bean curd) were 1.9-13.9 and 94.8-137.7 μg/g food, respectively. Levels of isoflavones in fermented soybean products, miso (bean paste) and natto (fermented soybeans), were 38.5-229.1 μg/g food for genistein and 71.7-492.8 μg/g food for genistin. Therefore, the levels of genistein in the fermented soybean products were found to be higher than in soybeans and soybean products such as soymilk and tofu. Soy sauce was also found to contain both isoflavones, but at levels lower than in miso and natto. Based on these results, the daily intake of genistein and genistin by the Japanese is estimated to be 1.5-4.1 and 6.3–8.3 mg/person, respectively. The authors note that these levels are much higher than those for Americans or Western Europeans, whose mortality rates for breast, colon and prostate cancers are greater than the Japanese rates.
