Way back in the fall, when I reviewed The Vegetarian Myth, I promised to follow-up with some perspective on the controversies surrounding soyfoods. I know that Jack Norris is working on a fairly comprehensive overview of this topic which will hopefully be available soon. I’ll be adding some information to my website as well. For now, I wanted to look at the important issue of soy consumption in Asia. It’s an area of some confusion since a common belief is that Asians consume only small amounts of soy—sort of condiment-style—and that they consume mostly fermented soy products like miso and tempeh. Based on the research, though, neither of these assumptions is true.
The confusion about how much soy Asians consume is based partly on a simple mathematical misunderstanding. In studies of intake, findings are sometimes expressed as the amount of soy protein that people consume—which is different from the total amount of soy food in their diets. For example, according to surveys in Japan, older adults consume around 10 grams of soy protein per day, which is the amount of protein in about 1 to 1 ½ servings of traditional soyfoods. Because a number of authors have misunderstood the relationship between soy protein and soyfood, they’ve greatly underestimated the amount of soy in Japanese diets.
Information about soy intake in Asia comes from a number of different resources including studies designed to examine the effects of diet on health, Japan’s National Nutrition Survey, and the Food and Agriculture Organization (FAO) of the United Nations. The most important of these are the studies designed to look at diet and disease relationships because many of them evaluated soy intake comprehensively. That is, they recorded frequency, and amounts of all types of soy products consumed using validated dietary intake instruments.
The results show a fairly wide range of intake among different countries and even within populations. While average Japanese intake is 1 to 1 ½ servings, the surveys reveal that the upper range among older Japanese—who would be expected to eat a more traditional diet—is about 3 servings of soyfoods per day.
It’s much harder to determine soy intake in China because diets vary greatly across regions. The most extensive data are available for Shanghai where large studies of health habits include dietary data from close to 100,000 adult men and women. Average intake in Shanghai is a little bit higher than in Japan. But the range of intake is extensive and a large number of the adults in these studies—as many as 15 to 20 percent of the men and 10 percent of the women—consumed 2 to 3 servings of soyfoods per day.
With the exception of Hong Kong, there isn’t quite as much data on soy intake in other countries and regions. But, the available findings suggest that, compared to Japan and Shanghai, soy consumption is much lower in Hong Kong and Thailand, about the same in Indonesia, and a bit higher in North Korea.
And contrary to popular opinion, the soy products regularly consumed in these countries are not all—or even mostly—fermented. In Japan, about half of soy consumption comes from the fermented food miso and natto and half comes from tofu and dried soybeans. In Shanghai, most of the soyfoods consumed are unfermented, with tofu and soymilk making the biggest contributions. In fact, even in Indonesia, where tempeh is a revered national food, unfermented soy products like tofu account for around half of soy intake.
Soyfoods have been consumed in China for at least 1,500 years and in Japan for 1,000 years. The evidence shows that soyfoods—both unfermented and fermented—continue to be a significant part of traditional Asian diets. There is no reason why western vegans can’t include these foods in meals as well.