Vaclav Smil

In July 1853, Commodore MatthewPerrys small flotilla cast its anchors offUraga at the entrance to Edo (Tokyo) Bay.Its mission was to end Japans quarter of amillennium of isolation under the Toku-gawa shogunate. The black ships returnedthe next spring, when Perry signed thetreaty. The shogunate was persuaded notjust by the ships large guns but also by thedemonstrations of American technicalsuperiority that included the telegraph anda miniature steam locomotive.

Mission accomplished, Perry returnedbearing samples of Japanese products. Aswell as the predictable silks, lacquer boxesand exquisite porcelain, these included whiteand red soy beans. Several months later theUS Patent Office was offering the seeds toAmerican farmers, but there were few takers.Three decades later, Lewis Sturtevant notedin his exhaustive survey of edible plants thatsoy beans had begun to appear as a noveltyitem in US seed catalogues.

In China their cultivation is ancient:nearly 5,000 years ago the legendary Emper-or Shennong made soy beans the onlylegume of his five life-sustaining grains, andmillennia of culinary evolution have pro-duced an enormous range of soy-basedfoodstuffs throughout East and SoutheastAsia. Immature pods are eaten as a vegetable.Mature seeds are sprouted or milled to makeflour. Protein in milled soy beans can be pre-cipitated by coagulants, usually calcium andmagnesium sulphate, to make bean curd Japanese tofu and Chinese dufu. Seeds areground or boiled and then fermented to pre-pare soy sauces and pastes such as Japanesemiso and natto and Indonesian tempeh. Andthe seeds, which are nearly 20% lipids, makean excellent cooking oil consisting of 85%unsaturated fatty acids. Modern processinghas also added an array of flavoured drinks totraditional soy bean milk.

The West was slow to adopt soy beans: inthe 1920s American farmers still devotedmore land to sweet potatoes. Soy beans final-ly took off in the 1930s, but it was the pros-perity following the Second World War, withits rising demand for cheaper meat, thatmade them a major crop. Corn has only 10%protein, but most soy bean cultivars haveabout 36%, nearly twice as much as otherlegumes. Mixtures of corn, a high-yieldingsource of carbohydrates, and highly pro-teinaceous (44%) soy bean meal, producedby first extracting oil with organic solvents,have come to dominate feeding formulas

around the world. American cattle, Germanbroilers, Japanese pigs and Chinese carp all yield more meat thanks to Glycine max.

The US soy bean harvest passed 10 milliontonnes (Mt) in the early 1950s. It is now 7075Mt a year almost half of the global total. Soybeans are the countrys second most valuablecrop, close behind corn and worth nearlythree times as much as wheat, and grow onmore than 15% of all arable land. Brazilianproduction, geared to exports, has growneven faster. The area planted with soy beanshas expanded more than 60-fold since the late1950s; Brazil now produces about 30 Mt.Argentina harvests about half as much as this,relegating the Chinese harvest to fourthplace. The Japanese now grow a mere 3% ofwhat they consume. Boiled tofu served in thetemple precincts of Kyotos Higashiyama ortofu-based nouvelle cuisine in Tokyos Ginzanow come from seeds harvested, and oftenorganically grown, in Iowa or North Carolina.

The symbiotic relationship between soybeans and the Rhizobium bacteria in nodules

attached to the plants roots can provide asmuch as 100 kg of nitrogen per hectare peryear. So it may come as a surprise to learn thatat least a fifth of the US crop now regularlyreceives nitrogen fertilizers. This is because ahigher proportion of the biomass of moderncultivars is in the seed, which is removedfrom the field. So, even with minimal lossesto leaching or erosion, more nitrogen isextracted than is fixed by bacteria. In con-trast, Brazilian soy beans receive no extranitrogen. Perhaps the most important envi-ronmental downside of soy beans rise is that,as with all other crops grown in rows, theircultivation can lead to higher soil erosion.

The worlds diet is unthinkable withoutsoy beans, but they remain a fringe foodstuffin the West. Only soy sauce has become a uni-versal condiment bean curd, althoughreadily available, is still a culinary oddity. Achange would serve women particularlywell. Soy bean foods contain very high con-centrations of isoflavones, particularlygenistein. These phytoestrogens can alleviatethe symptoms of menopause, and their con-sumption has been linked to reduced risks ofbreast cancer in East Asia. Soy proteins alsolower levels of blood cholesterol, and some,although not all, epidemiological studieslink their intake with a reduced risk of car-diovascular diseases. Greater enthusiasm forthe subtle taste of tofu could thus have highlycost-effective health benefits. Vaclav Smil is at the University of Manitoba,Winnipeg, Manitoba R3T 2N2, Canada.

Magic beansThe Japanese invader thats good for you.

millennium essay

NATURE | VOL 407 | 5 OCTOBER 2000 | www.nature.com 567

Soy beans are thesecond mostvaluable US crop, andgrow on more than 15%of all arable land.

Soy ahoy: the beans reached the West via Perrys black ships, shown here arriving off Tokyo in 1853.

BR

ITIS

H M

USE

UM

/BR

IDG

EM

AN

AR

T L

IBR

AR

Y