People in Japan and other Asian countries consume only small amounts of soyfoods and use them primarily as condiments.
|Soy intake varies greatly among Asian countries, but in Japan and some locations in China for which there are excellent data, soyfoods play an important dietary role providing substantial amounts of protein and calories.|
Over the past decade a large amount of information on the soy intake of Asians has been published in the peer-reviewed medical and scientific literature. This information generally comes from large surveys often involving tens of thousands of individuals who fill out food frequency questionnaires (FFQ) or in some cases dietary records (in which all food consumed is recorded). The FFQs are designed to comprehensively evaluate the intake of all soyfoods by asking a series of questions about the kinds, amounts, and frequency of soy consumption. In most cases the FFQs are scientifically validated – meaning they have been shown to be an accurate instrument for assessing dietary intake.
The results from these surveys indicate that on average older (>50 years) Japanese adults and older adults in Shanghai consume about 9 grams of soy protein per day. This figure represents about 10% of total protein intake of these populations . One study from Shanghai that is especially notable because of its size reported that among the ~50,000 men that filled out a FFQ, average soy protein intake was almost 13 grams per day  . For comparison, one serving of a traditional soyfood provides anywhere from about 7 (1 cup soymilk) or 8 grams (1/2 cup edamame) to as many as 20 grams (1/2 cup very firm tofu) protein per serving.
The population of Japan is a rather homogeneous in regard to their dietary habits so soy consumption is relatively similar throughout the entire country In contrast, the population in China is rather heterogeneous in regard to their dietary habits such that soy intake in some locations is much higher than in others. Consequently, little is learned by discussing overall soy intake in China. It is a bit like describing the average intake of grits in the United States; this food is consumed in the South but almost not at all in other geographical areas. Thus, when speaking about soy intake in China it is necessary to specify the geographic location in question.
Soy intake is often incorrectly portrayed in lay publications because of confusion over the dry weight and wet weight of food and because the amount of soy protein consumed is often equated with the amount of soyfoods consumed. For example, it is sometimes stated that Japanese consume less than a tablespoon of soy protein per day. This is absolutely correct because a tablespoon is generally regarded as weighing 14 grams. (In the United States dairy foods provide about 14 grams of protein per day). However, it is also true that the average woman only consumes about 5 tablespoons (70 grams) of total protein (from all sources) in the entire day and men a just little more than that.
Of course, the actual amount of food one needs to consume to obtain these amounts of protein is quite a bit larger. This is because food is a largely comprised of water. For example, cooked rice and beans are about two-thirds water and most fruits and vegetables about 80 to 90% water. And protein is just one of the three macronutrients, the other two being fat and carbohydrate. Consequently, 9 grams of soy protein is provided about 320 milliliters of soymilk or about 1.3 cups.
Finally, the soy intake values discussed above represent averages. It is useful to have some understanding of the upper range of soy intake in Asia because the average amount of a particular food or nutrient consumed is not necessarily the ideal amount. Certainly, the average intake of calcium or fruits and vegetables in the United States is less than ideal. In Japan and Shanghai, people in the upper fourth or fifth intake categories (i.e., those whose intake exceeds more than 75 or 80% of the population) generally consume about 15 to 20 grams of protein per day, or about twice the average amount [3, 4]. These amounts are provided by about two to three cups of soymilk. In regard to the type of soyfoods consumed, although the first soyfoods consumed were fermented (e.g., miso and natto), there are historical records indicating that in Japan, nonfermented foods (e.g., tofu and cooked soybeans) have been consumed for at 1000 years. Today, slightly more than half of the soy consumed in Japan is in nonfermented forms whereas in China, the percentage is quite a bit higher .
It is obvious from the above discussion that in some Asian populations such as Japan and Shanghai that soyfoods play an important dietary role. Soyfoods are the not primary sources of protein in the Japanese diet as is sometimes stated but nor do they function primarily only as condiments. Whenever possible, nutrients should come from a variety of sources because all nutritious foods bring something to the table. Thus, soyfoods are best viewed as one group of healthful foods that can help meet protein needs.
- Messina M, Redmond G: Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid 16, 249-58 (2006).
- Lee SA, Wen W, Xiang YB, Barnes S, Liu D, Cai Q, et al.: Assessment of Dietary Isoflavone Intake among Middle-Aged Chinese Men. J Nutr 137, 1011-6 (2007).
- Yang G, Shu XO, Jin F, Zhang X, Li HL, Li Q, et al.: Longitudinal study of soy food intake and blood pressure among middle-aged and elderly Chinese women. Am J Clin Nutr 81, 1012-7 (2005).
- Cui X, Dai Q, Tseng M, Shu XO, Gao YT, Zheng W: Dietary patterns and breast cancer risk in the shanghai breast cancer study. Cancer Epidemiol Biomarkers Prev 16, 1443-8 (2007).