Soy Plays Important Role in Asian Diets, But Consumption Varies Among Countries
By Mark Messina, PhD, Executive Director, Soy Nutrition Institute
Despite their long history in Asian cuisine, there is plenty of confusion about how much soyfoods people in China, Japan and other Asian countries consume. A quick search of the internet brings up claims that soy is used condiment-style in this part of the world with most people consuming as little as a tablespoon of soy per day. And most of that, according to the internet, is fermented.
This would all come as a surprise to the millions of Chinese who start their morning off with a cup of hot fresh soymilk and then later in the day might stir tofu into a meal that also contains some meat and vegetables.
It’s surprising that so much misinformation about Asian soyfood intake makes the rounds on blogs and in social media since there are numerous studies that have evaluated the intake of thousands and thousands of Asians. And, unlike other types of research, information about dietary intake is straightforward and objective. There is little room for individual interpretation.
There is, however, room for confusion about how intake is measured, and this is the source of much of the misinformation on this topic. Soy consumption data often provide the amount of soy protein consumed by individuals, so it’s necessary to do some calculations in order to translate that to the total amount of soyfood consumed. For example, one study found that older people in Japan consume, on average, 8 to 10 grams of soy protein per day. This translates to about 1 to 1½ servings of tofu, soymilk, or edamame.
While information on dietary habits throughout Asia is readily available, there is no single answer to this question: “How much soy do Asians eat?” The types and amounts of soy consumed vary among countries and even among regions within the same country.
The best information about Asian soy consumption comes from the many large Asian prospective and case-control studies that have evaluated the relationship between soy intake and a variety of health outcomes. In most instances these studies used validated food frequency questionnaires (FFQs) to comprehensively assess soy intake. The FFQs include multiple questions about the types, amounts, and frequency of soyfoods consumed. Different databases are used to then estimate the amount of isoflavones and soy protein provided. Using these metrics to express soy intake allows for better standardization and comparisons among studies than does the wet weight of food.
One analysis from the Shanghai Women’s Health Study (n=45,694) reported that daily mean intake of soy protein was 8.8 ± 6.3 grams.1 But the range of soy intake was wide. Slightly more than 2 percent of the women consumed at least 25 grams of soy protein per day while around 9 percent consumed less than 2.5 grams per day. The Shanghai Men’s Health Study (N=54,219) reported that daily mean intake of soy protein was 12.5 ± 7.94 grams.2 However, soy consumption varies considerably throughout China, and in some regions is one-third to one-half lower than in Shanghai.
Soy intake in Japan is more consistent throughout the country and is similar to what is found in Shanghai. Men enrolled in the Takayama Study (N=13,888) consumed 11.3 ± 7.8 grams of soy protein per day and women (N=16,424) consumed slightly less at 10.5 ± 7.0 grams.3 A much smaller study by the same author reported an intake of only about 8 grams of soy protein per day for men and 7 grams for women. But in both Japan and Shanghai, individuals in the fourth quartile or fifth quintile intakes consumed 15 grams or more of soy protein daily.
The type of soy consumed varies among countries as well. In China, Singapore and Hong Kong, unfermented soyfoods, particularly tofu and soymilk, are the most commonly consumed products. 4 In Japan, about half of soy intake comes from the fermented foods natto and miso and the rest is tofu. 5,6
Finally, soy protein intake can be used to estimate isoflavone intake. In traditional soyfoods like tofu, soymilk and tempeh, each gram of protein is associated with approximately 3.5 mg of isoflavones. More refined products (such as isolated soy protein) are typically much lower in isoflavones, however, which are lost during processing.
While soyfoods consumption varies greatly throughout Asia, the research answers important questions about intake. It is clear that soyfoods play an important role in the diets of many Asians and that both fermented and non-fermented foods contribute to intake.