Silk®s Nutrition Team
Nutrition
- Are fermented soyfoods nutritionally superior to unfermented soyfoods?»
- How much soy protein is recommended for daily consumption?»
- Is soy protein a complete protein?»
- How can consumers determine how much soy protein is in a food?»
- Is there an FDA recommendation for daily isoflavone intake?»
- Do isoflavone supplements provide the same benefits as eating soyfoods?»
- Is it possible to consume too much soy protein?»
- How can I get soy in my diet?»
- How much soymilk can be consumed on a daily basis?»
- Besides tofu and soymilk, what other forms of soy are there?»
- Are there any health benefits to consuming soy? How much soy can be consumed on a daily basis?»
- Is soymilk high in calories?»
- Is there a nutritional difference between yellow soybeans and other soybeans?»
- Is soy a protein or a carbohydrate?»
- Is soymilk good or bad for our health?»
- How many grams of protein are in 1/4 cup of dry-roasted soybeans?»
COMMON QUESTIONS
Are fermented soyfoods nutritionally superior to unfermented soyfoods?
Both fermented (natto, miso) and unfermented (tofu, soymilk) soyfoods have been widely consumed throughout Asia for centuries. It is often stated that fermentation improves the digestibility of soy protein. However, the digestibility of soy protein from unfermented products is already excellent—typically exceeding 90%.1
Fermentation does reduce the phytate content of soy, which is quite high, but it is not clear that this reduction leads to a meaningful increase in mineral absorption in humans.2,3,4 There may also be a decrease in trypsin inhibitor content,5 but the relevance of this change is unclear since in commercially available soyfoods, the amount of trypsin inhibitor is already so low as to be clinically irrelevant.6,7
Finally, fermentation does lead to the creation of antioxidants and peptides, but the effects of these newly created compounds in humans have not been established.8,9
There is little basis for claiming that fermented soyfoods are superior to unfermented ones, and there is certainly no evidence that fermented foods are better able to provide the proposed health benefits of soyfoods than unfermented ones. Both types of soyfoods are good choices for individuals wanting to incorporate more soy into their diet.
Featured Expert
Dr. Messina is the co-owner of Nutrition Matters, Inc., a nutrition consulting company, an adjunct associate professor at Loma Linda University, and the Executive Director of the Soy Nutrition Institute. Full bio >>
References
1. Gilani GS, Sepehr E. Protein digestibility and quality in products containing antinutritional factors are adversely affected by old age in rats. J Nutr. 2003;133:220-5.
2. Zhao Y, Martin BR, Weaver CM. Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow’s milk in young women. J Nutr. 2005;135:2379-82.
3. Murray-Kolb LE, Welch R, Theil EC, Beard JL. Women with low iron stores absorb iron from soybeans. Am J Clin Nutr. 2003;77:180-4.
4. Lonnerdal B, Bryant A, Liu X, Theil EC. Iron absorption from soybean ferritin in nonanemic women. Am J Clin Nutr. 2006;83:103-7.
5. Ibrahim SS, Habiba RA, Shatta AA, Embaby HE. Effect of soaking, germination, cooking and fermentation on antinutritional factors in cowpeas. Nahrung. 2002;46:92-5.
6. Garthoff LH, Henderson GR, Sager AO, Sobotka TJ, Gaines DW, O’Donnell MW, Jr., Chi R, Chirtel SJ, Barton CN, et al. Pathological evaluation, clinical chemistry and plasma cholecystokinin in neonatal and young miniature swine fed soy trypsin inhibitor from 1 to 39 weeks of age. Food Chem Toxicol. 2002;40:501-16.
7. Garthoff LH, Henderson GR, Sager AO, Sobotka TJ, O’Dell R, Thorpe CW, Trotter WJ, Bruce VR, Dallas HL, et al. The Autosow raised miniature swine as a model for assessing the effects of dietary soy trypsin inhibitor. Food Chem Toxicol. 2002;40:487-500.
8. Fan J, Zhang Y, Chang X, Saito M, Li Z. Changes in the radical scavenging activity of bacterial-type douchi, a traditional fermented soybean product, during the primary fermentation process. Biosci Biotechnol Biochem. 2009;73:2749-53.
9. Kim NY, Song EJ, Kwon DY, Kim HP, Heo MY. Antioxidant and antigenotoxic activities of Korean fermented soybean. Food and Chemical Toxicology. 2008;46:1184-9.