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First International Symposium on the Role of Soyin Preventing and Treating DiseaseModern Applications for an Ancient Bean: Soybeans andthe Prevention and Treatment of Chronic Disease1

MARK M ESSINA1543 L incoln Street, Port Tow nsend, WA 98368

ABSTR ACT Soybeans have played an integral part inAsian culture, both as a food and as a medicine, form an y centu ries. In the W est, soybean s are b est know nfo r th eir p ro tein con ten t b ut in cre asin gly , soy fo od s a rebeing recognized as having potential roles in the prev en tio n and tr ea tm en t o f c hr on ic d is ea se s, mo st n ota blyca nce r a nd h ea rt d isea se . T here a re a lso p oten tia l ro lesfor soyfoods w ith respect to osteoporosis and kidneyd ise ase . A lth ou gh mor e r es ea rc h is n ee de d, th e e xistin gd ata ba se o n th e h ea lth effec ts o f so yfo od in tak e is q uiteex ten siv e a nd clea rly w arra nts g rea ter reco gn itio n b ythe research and clinical commun ities. G iven th e easew ith w hich soyfoods can b e incorporated into the d iet,be it via the traditional soyfoods such as tofu and soy-m ilk, or the m ore m odern soy protein products, suchas soy isolates, concen trates and flou rs, soyfoods m ayb e a ble to h av e a sig nifica nt b en eficia l im pa ct o n p ub lichealth. J. Nutr. 125: 567S-569S, 1995.IN DEX ING KEY WORDS:s ofl av on es s oy fo od s c an ce r h ea rtd is ea se o ste opor os is k id ne y d is ea sep ro te in ch roni c d is ea se soybeans

In China the word for soybean is ta-tou, whichmeans "greater bean" (Simoons 1991). This is notsurprising given the importance soybeans haveplayed in Asian culture, both as a food and as a medicine. In the W est, soybeans are still best know n fortheir protein content. In com parison to m ost otherlegumes, soybeans are much higher in protein(~35% of energy). However, it is not only theamount of protein in soybeans that is notable, butalso the am ino acid pattern of soy protein. Despiterecognition of soybeans as an excellent source ofprotein, the quality of soy protein has actually beenu nd erv alu ed u ntil rece ntly .T he co nv en tio nal assa y fo r ev alu atin g p ro tein q uality, the protein efficiency ratio (PER), i s based on thegrow th of laboratory rats. G row ing rats not only have0022- 3166 /95 $3.00 1995 Amer ic an In stitu te o f Nu tr itio n.

a m uch higher total protein requirem ent than do infants, but also a m uch higher need for certain am inoacids than hum ans (Steinke 1979). In particular, therat requirem ent for m ethionine is ~ 50% higher (Sarwar e t a l. 1 985); c on sequ en tly , th e v alu e o f so y p ro te inh as b ee n u nd erv alu ed b eca use th e lim itin g amin o ac idin so y pro te in is m eth io nin e.In recognition of the inadequacy of the PER andthe expense and tim e required to conduct these tests,both the W orld H ealth O rganization and the U nitedStates Food and Drug Administration adopted theprotein digestibility corrected amino acid score(PDCAAS) a s th e o ffic ia l a ssa y fo r e va lu atin g p ro te inquality. The PDCAAS represents the amino acidscore (using am ino acid requirem ents for 2-5-year-old children) after correcting for digestibility. Proteins th at, a fter co rre cting fo r d ig estib ility , p rov ideam ino acids equal to or in excess of requirem ents,receive a PDCAAS of 1.0. Soy protein has a PDCAASof 1.0, indicating it is able to m eet the protein needsof adults when consumed as the sole source of protein at the recommended level of protein intake (0.6g/kg body w t) (Y oung 1991).It is som ew hat ironic that as the high quality of soyp ro te in gain s g reate r recogn ition, nutri tiona l emphas ison m eeting protein requirem ents has dim inished.D uring the 1950s, considerable effort w as expendedtow ard elim inating w hat w as referred to as the w orldp ro te in g ap . B y t he 1 97 0s, h owev er, it w as rec og nize dthat the world protein gap was not so m uch a proteingap, but rather a food gap. This undue em phasis onprotein w as partially a result of an inflated estim ate

1P re se nte d a t th e F irst In te rn atio na l S ympo sium on th e R ole o fS oy in P re ve ntin g a nd T re atin g C hro nic D ise as e, h eld in Mes a, AZ,F eb ru ary 2 0-2 3, 1 99 4. T he symposium was sp on so re d b y P ro te inT echnol og ie s In te rn ati on al, th e s oybe an g rower s fr om Nebr as ka ,In dia na , a nd Iowa a nd th e U nite d S oy be an B oa rd . G ue st e dito rs fo rthis sym posium w ere M ark M essina, 1543 L incoln Street, PortT ow nsen d, WA 9 836 8, an d Jo hn W . E rdman , Jr., D iv isio n of N ut ri ti ona l Sc iences, Un ive rs it y o f I ll ino is , U rbana, IL 61801-3852 .

567S

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568S SUPPLEMENTo f p ro te in requ irements , particul arly f o r in f an ts . From1948 to 1974, e stima te s o f in fan t p ro te in re qu iremen tsd ec re ased b y tw o -th ird s (C arp en te r 1 986 ). T he re w asalso an unw arranted em p hasis on the need f or anim alfoods to m eet protein requirem ents. A s long ago as1946, how ev er, H egsted correctly stated that as longas caloric needs are adequately m e t, it is dif ficult notto also meet p ro te in re qu iremen ts; th is is p artic ularlytrue f or adults (H egsted et al. 1946).T his is not to say that the protein f raction of soyb ean s is u nimp ortan t; it is, n ot o nly f or m e etin g am i noacid an d n itro gen req uirem e nts, b ut also f or o the r reasons. S o y p ro te in is v e ry e ff ic ie ntly p ro du ced; appro xim ately 25, 10 and 5 tim es m ore protein is producedw hen an acre of land is dev oted to grow ing soy beansas com pared w ith beef , m ilk and w heat production,re sp ec tiv e ly (Christian se n 1948). A lth ough th is is n ota nutritio nal issu e p er se , it is n on eth ele ss n oteworth y ,because there are increasing concerns about the ef ficient use of land and w ater resources. T he soy beanalso re pre se nts an in exp en siv e so urc e o f h ig h-q ualityprotein, w hich m ay be particularly im p ortant f or deve lop ing countri es .From a nutritional perspectiv e, soy protein m ayh old man y ad vantag es o ver an imal p ro tein s ab ov e an dbey ond the f act that soy beans are low in saturated f atand, o f cours e, cho le st ero l-f ree. O f u tmos t importanceis th e h yp oc ho lesterolem ic ef fec t o f so y p ro te in as d iscussed by sev eral authors in this v olum e. A s little as25 g of soy protein is all that is needed to low er chole ste ro l in h ype rc ho le ste ro lem ic su bje cts (B akh it e t al.1994), thus soy protein represents a saf e, v iable andpractical nonpharm acologic approach to low eringcholesterol.S oy protein m ay also help to prom ote bone health.Factors af f ect ing urinary calcium excre tion p lay cri ti calro le s in d ete rm i nin g calc ium balan ce and bon e m i ne rald en sity . T h e h yp erc alc iu ric ef fect o f p ro tein h as be enproposed as one f actor contributing to the high ratesof osteoporosis in W e stern countries (A below et al.1 992 ), w h ere p ro tein in tak e g reatly e xc ee ds req uirements. S tu die s in dic ate , h ow ev er, th at n ot all p ro te in sare sim i lar in th is re sp ec t, an d th at in c omp ariso n w ithan ima l p ro te in s, so y p ro te in c au se s much le ss c alc iumto be ex creted in the urine (B reslau et al. 1988). T hisis lik ely a result of the som ew hat low er sulf ur am inoacid content of soy protein. Parenthetically , the iso-f lav ones in soy beans m ay also directly inhibit boner so rp tio n(B randi 1 992; A nde rso n e t al. 1 995); th ussoy beans m ay w ork in sev eral im portant w ay s to aidin bon e h ealth .S oy protein m ay also hav e a role in the prev entionan d treatm e nt o f k id ne y d isease , b ec au se so y pro te in ,in com parison w ith som e anim al proteins, has beenfound not to adv ersely af f ect k idney function (K on-te ssis et al. 19 90 ). Fo r t his re aso n, K o ntessis e t al. su ggested that k idney disease patients w ould benef it asm uch by substituting soy protein for anim al protein

as b y re stric tin g o v erall p ro te in in tak e . Fu rth ermo re ,th e h yp och ole stero lem i c ef fe cts of so y p ro te in may b eo f p articu lar b en ef it to p atie nts w ith ch ron ic ren al insu ff ic ie nc y , b ecau se e le v ate d le v els o f c ho le ste ro l c anexacerbate d is ease progress ion (Groet al . 1994). Theox idation o f low -density l ipopro te in (LDL) chole ste ro lmay p lay a critic al ro le in this reg ard ; c onse qu en tly ,the suppression of LDL-cholesterol ox idation by soyprotein m ay be still another benef it of soy protein noton ly to k id ne y d ise ase p atie nts, b ut also to the g ene ralpub li c (Kanazawa 1994).R esearch on the potential health benef its of soy -f oods is p artic ularly in trig uin g w i th re sp ec t to c an ce rprev ention and treatm ent. A s discussed in this v olum e and elsew here, epidem iologie data suggest theconsum ption of as little as one serv ing of soy foods(i.e., one cup soym ilk , 5 cup tofu) per day low ersrisk f or a w ide range of cancers (M e ssina et al. 1994).A l th ou gh certain ly sp ecu lativ e, this is th e area w h eresoy foods m ay hav e their greatest im pact on publich ealth . If th e h ypo the siz ed an tic an ce r e ff ec ts are d ueto the isof lav ones, this places particular em phasison soy , because the isof lav ones hav e a v ery lim itedd istrib utio n in natu re .W hen one considers the m any nutritional attributes of soy foods, f rom the v ery basic (high-qualityp ro te in , lac to se f re e and cho le ste ro l f re e, g ood sourc eof om ega-3 f atty acids) to the m ost ex citing (the prev ention and or treatm ent of heart disease and cancer), it is clear that the nutrition comm unity shouldw elcom e the incorporation of soy foods into theA m erican diet. Fortunately , the m ultitude of foodproducts m ade f rom soy beans, f rom the traditionalEastern ones, such as tofu and soy m ilk , to the m orem odern ones, such as soy hot dogs and burgers,m ak es increasing soy food consum ption an achievab le goal.

L IT ER AT UR E C IT EDAbe low , B . J. ,Ho lf o rd ,T . R . & .I ns ogna, K .L . ( 1992 ) C ro ss -c ult uralass oc iatio n b etw e en d ie tary an im al p ro te in an d h ip f rac tu re : ah ypo th es is . Calc if . T i ss ue I nt. 5 0: 14- 18 .A n derson, J. J., A m brose, W . W . , & G arner, S . C . (1995) O rallydosed G enistein f rom S oy and Prev ention of C anellous boneloss in tw o ovariectom ized rat m odels. J. N utr. 125: 799Sfabs.),B ak hit, R . M . , K le in , B . P., E sse x-S o rlie , D ., H am , J. O ., E rdman ,J. W ., Jr. & Potter, S . M . (1994) Intak e of 25 g of soybeanpro tein w ith or w ith ou t so yb ean f ib er alters plasm a lip id s inm en w ith elev ated cholesterol concentrations. J N utr 124:213-222.B ran di, M . L . (1 99 2) Flav o no id s: b io ch em ic al e ff ec ts an d th erapeu ti c app li ca ti ons. Bone Mineral . 19 (supp l) : S3 -S14.B reslau, N . A ., B rink ley , L ., Hill, K . D. & Pak , C. Y . C. (1988)R elatio nsh ip of an im al pro tein -rich d iet to k id ney sto ne f orm atio n an d calciu m m etab olism . J C lin E ndo crin ol M e tab 6 6:140-146.C arpenter, K . J. (1986) T he history of enthusiasm f or protein. JNu tr. 1 16 : 1364- 1370 .

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MODERN APPLICATIONS FOR AN ANCIENT BEAN 569SC hristiansen, R . P. (1948) Efficacious use of food resources in theU nited States. U .S.D .A . T echnical B ulletin no. 963. U .S. G overnm ent P rinting O ffice, W ashington, D .C .G rone, E . F ., W alli, A . K .., Grone, H -J., M iller B ., S eidel, D . (1994).T he role of lipids in nephrosclerosis and glom erulosclerosis.A th ero sc le ros is 1 07 : 1-1 3.Hegsted, D . M ., Tsongas, A . G., Abbott, D . B., Stare, F . J. (1946)Protein requirem ents of adults. J L ab C lin M ed 31: 261-284.Kanazawa, T. (1994) Inhibition of LDL oxidation and atheromaform ation by soy protein. J. N utr. 125: O OO S-O OO S.K ontessis, P., Jones, S., D odds, R ., T revisan R ., N osadini, R ., Fioretto, P., B orsaio, M ., Sacerdoti, D ., V iberti, G . (1990) R enal,metabolic and hormonal responses to ingestion of animal andvegetable proteins. K id Inter 38: 136-144.

M essina, M . J., Persky, V ., Setchell, K . D. R., Barnes, S. (1994)Soy intake and cancer risk: a review of the in vitro and in vivodata. N utr C ancer 21: 113-131.Sarwar, G ., R . W . Peace, and H. G. Bolting. (1985) Correctedrelative net protein ratio (C RN PR ) m ethod based on differencesin rat and human requirements for sulfur am ino acids. J Am OilC hem S oc 68: 689-693.Simoons, F. J. (1991) Food in China. A Cultural and HistoricalInquiry. C RC Press Inc., B oca R aton, FL.Steinke, F. H . (1979) M easuring protein quality of foods. In: SoyProtein and Human Nutrition (W ilcke, H . L., Hopkins, D . T.,and W aggle, D . H ., eds.) A cadem ic Press, N ew Y ork.Young, V. R. (1991) Soy protein in relation to human protein andam ino acid nutrition. J A m D iet A ssoc 91: 828-835.

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