am j clin nutr 1995 cummings 938s 45s

7/28/2019 Am J Clin Nutr 1995 Cummings 938S 45S

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938S A m J C lin N u tr 1995 ;6 1(su pp l):9 38S-4 5S . P r in te d in USA . 1995 Am eric an S ociety for C lin ica l N u trition

G as tro in tes tin a l e ffec ts o f fo o d ca rb oh yd ra t& 3John H C um m ings a nd H ans N E ng lyst

ABSTRACT D ie tary ca rboh ydra te m ay b e d iv id ed in tom onosaccharides and d isaccharides (sug ars), o ligosacchan ides[degree o f po lym eriza tion (DP ) 3-9 ] , and po ly sacchan ides (DP> 10). T he ir ph ysio log ica l p ro pe rtie s and h ea lth ben efits d e-p end on the s ite , ra te , an d ex ten t o f the ir d ig estion or ferm en -ta tion in the g u t. O ligosacchan id es a re a d iverse g roup ofso lub le carbohyd ra tes , m any of w hich are n o t d igested bypancrea tic enzym es. T hey are fe rm en ted in the co lon and som ehave sp ec ific e ffec ts on bac te ria . T he m ajo r d ie ta ry p o lysac-charides a re s ta rch and nons ta rch p o lysaccharides (NSP s). T hed igestion of s ta rch depends on its phys ica l fo rm , th e n atu re o fthe s ta rch granu le , and the effec ts o f fo od process in g . S ta rchm ay be rap id ly d ig es ted , slow ly d igested , o r resistan t, the las tpasses in to the co lon fo r fe rm en ta tion . T he N SPs (ce ll w a llpo lysacchan ides) a ll res ist d igestion . T hey ex er t a phy sica le ffect in the upp er gu t, se rv ing to m odera te ca rbohydra te andpossib ly lip id abso rp tion , w hereas in the co lon they affectbow el hab it th rough fe rm en ta tion , they affec t ep ithe lia l ce llm etabo lism , and , a long w ith o ther fe rm en ted carboh ydra tes,th ey pro v ide en ergy to h um ans. A m J C lin N u tr 1995 ;61(supp l) :938S-45S .

K EY WORD S Carbo hydra te , s tarch , o ligosacchan ides ,n onsta rch po lysacchan ides , d igestion , fe rm en ta tion , recom -m ended intak es

IntroductionO ur und e rstand ing o f th e d igestive p hysio logy an d h ealth

benefits o f d ie ta ry carboh ydra te has changed su bstan tia lly inthe pas t 20 y . T he p o lysacchan ides o f th e p lan t ce ll w a ll ( fib e r)a re no long er thou gh t o f as ine rt m ater ia l p assin g th roug h thegu t and sim p ly affec ting b ow el hab it (1 , 2 ). T hey cons is t o f arange of p o lym ers w ith con trasting p hysio lo g ica l e ffec ts. T h ep lan t ce ll w all po lysacchan ides , o r n ons ta rch p o lysacchan ides( NSPs), can a ll be m easu red an d ch arac te rized as th e sum ofthe ir cons tituen t sug ars (3 , 4 ). S ta rch is now known not to b erap id ly and com plete ly d igested in the sm all bow el and theconcep t o f resistan t sta rch h as been deve loped (5 , 6) w ith itsa ttendan t im plications fo r g lycem ic co n tro l an d la rge bow elfunc tion . M ore recen tly the im portance o f a prev iou sly n e-g lected gro up of carbo hydra tes, th e o ligosacchan ides , hasem erg ed as the resu lt o f the be lie f tha t they m ay affec t m ic ro -b ia l fun c tion in the la rge in testine in a benefic ial w ay (7 ). W ithth is know ledge h as com e a ca ll fo r be tte r food labe ling ofd ieta ry carbo hydra te an d there fo re a new look a t its c lass ifica-tion and m easurem en t.

C lass ify in g food ca rboh ydra te: chem istry com paredw ith fun ctio n

A c la ssif ica tion of foo d carbo hyd ra te fo r n u tr itio na l pu rp osesm ust fu lfill m any crite ria if po ss ib le ; n am ely , th e c lass ifica tionshou ld inc lu de all k now n die ta ry sub stances tha t a re d ef in ed bythe te rm carboh ydra te , a llow clea r bou ndaries to be drawnb etw een gro ups , p rov ide the an a ly st w ith an ach ievab le ob jec-tive , an d g ive th e consum er and o th er use rs use fu l and re liab lein fo rmat ion .

C arbohyd ra tes a re po ly hydro xya ldehydes and k eton es tha thave the em pirica l fo rm u la (CH 2O ) and the ir de riva tives (8 ).Fo r nu tritiona l purpo ses they are best c lass ified prim arily ac -co rd ing to th e degree of p o lym erization w ith subd iv is io nsbased on g lyco sid ic link ag es and chem is try of ind iv idu a l su g-ars b ecause these d ete rm ine physio log ica l p ro pertie s . T ab le 1show s such a classifica tion , w hich prov id es a log ica l approachto food carbohydra te and defines ca tegories tha t a re read ilym easurab le ana ly tica lly . H ow ever, it does no t equ ate w ith thesite o r the ex ten t o f d iges tion of ca rboh ydra te in the gu t, ap roperty o f som e im po rtan ce in de te rm in ing hea lth benefits . A sm ay b e seen from Tab le 1 , a w id e varie ty of chem ica l typ es o fca rb ohydrate are no t d ig ested in the u pper gu t. A ltho ugh it ispo ss ib le to m easure in the lab ora to ry a ll the carb ohyd ra tefrac tions lis ted in T ab le 1 w ith reasonab le accuracy , no m ethodex is ts tha t w ill d iv ide th em physio log ica lly in to , fo r exam ple ,d iges tib le and und iges tib le (ava ilab le and un ava ilab le ) frac -tions (9 ). T he phy sio log ica l p ro pertie s in the gu t o f the d iffe r-en t categor ies o f ca rboh ydra te overlap in m any respec ts.

Oligosacchar idesO ligo sacchan ides are ca rboh ydra tes w ith a degree of po ly -

menization (DP ) of 3 -1 0 (1 0). T hey a re read ily so lub le andinc lude tn - and te trasacch an ides su ch as raf finose and stachy-ose , m altodex tn ins from partial h ydro lys is o f s ta rch , p yrodex-tn ins p rod uced by hea tin g s ta rch in ac id con d ition s, fruc to - andga lac too ligo saccharides, and som e in u lin s. P yro dex tn in prepa-ra tions a re m ark eted in Japan fo r the ir hea lth -g iv ing propertie sas d rink s. Py rodex trins a re tho ugh t to be p oorly d igested . T hetn isacchan id e (G al-G ic -F uc) ra ffinose and te trasacchan ide (G al-G al-G lc -F uc) stachyo se are foun d in leg um es and because o f

1 From the M RC D unn C lin ica l N utr itio n C entre , C am b rid ge, UK .2 Suppo rted by the UK M inis try o f A g ric u ltu re , F ish erie s and F ood , and

by R affine rie T irlem onto ise , l ien en , B elg ium .A dd res s reprin t requ ests to JH C umm ings , M RC D unn C lin ic al N utr i-

tion C entre , H ills R o ad , C am bridge , C B2 2DH U nited K ing dom .


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U) t5a) .c .!:2 #{ 149} V0 1 (I) :- 0C. ) 0 - # {149}D C .)

EFFECT S O F FOOD CA R B OHY DR A T E IN T H E GUT 9395T A B L E 1C hem ical c lassif ication o f f o od carboh y drate s

T y pe of carbohy d rate (com ponents)D iges tio n andab sorptio n in

the sm allin tes t ine

M ono saccharid e, DP = 1G lu cose, f ru cto se +S orbito l, m ann ito l, e tc

D isaccharid e, DP 2S uc rose, m altose +L ac to se, lac tito l, m altito l, etc

O ligo saccharid e, D P >3 , 10S tarc h ( a- gl uc an s)

Amy l o s e Amy lop ec t i n M odif ied s tarches

N on starch (n on-a-g lucans ) poly sacchanidesC ell w all and chem ically re lated po ly m ers

Cellulose -Hemicellu loses -Pectins -

StorageIn ulin s (f ru ct an s) -Guar -

Plan t g um s, ex udates , and seed m uc ilagesIsp aghula, sterculia, k aray a -

D P, degree o f po ly m eriz ation .

th e ir no nd igestib ility in the sm all bow e l p ro v ide subs trate s f o rbac terial f e rm en tation in th e co lon , e specially gas f o rm ation(1 1 , 1 2 ). S ev eral o ther possib le health b en e f its are curren tly o fin te re s t (13 ).

It is how ev er th e f ruc too ligo sacchan ides th at hav e arou sedin te re s t in recen t y ears , m o stly becau se o f the ir p ro perty tostim u late the g row th o f b if ido bacte ria in the co lo n , f irs t de -scn ibed by Y az aw a and T am ura (1 4 ) and Y az aw a e t al (15 ).Po ly m ers and o ligo saccharides o f f ruc to se are sy n thes iz ed bym an y p lan ts and are f o und in th e hum an d ie t in on io ns, garlic ,artichok es, and ch ico ry , w h ich prov id e up to 1 2 g /d (16 ). T hebest k now n are the inu lin s , a g roup o f f 3 (2 -1 ) lin ear f ru c to sepo ly m ers w ith a D P 60 . Fruc too ligo sacch an id es are p roducedin tw o w ay s , e ith e r b y partial hy dro ly s is u sing endog ly co si-dase s , f o r ex am p le R af tilo se (O raf ti, T ienen , B elg ium ), w h ichis m ade f rom ch ico ry inu lin , o r by sy n thes is f rom su cro seby u sing f un gal /3 -f ru cto f lu ronos idase , eg , N eo sug ar (M eiji,K anagaw a, Japan ) (17 ).

Fruc to o lig o sacchan ides m ay b e partly hy d ro ly z ed by gas tricac id (9 , 18 ) , bu t in gen eral they are tho ugh t to e scape d iges tionin the hum an up per in te stin e com p le te ly (16 , 19 , 2 0 ) and toth en be f e rm en ted by the co lon ic m ic ro f lo ra (21 , 22 ). T he irm ost im portan t p rop erty , w h ich m ay be u n ique , is to s tim u lateb if idobac ten ial g row th spec if ically w h ile supp ress ing thegrow th o f som e o ther spec ies such as C los tr id ium pe ifr ingens .

In v itro f ruc to o ligo sacchan ides are f e rm en ted m o stly to ac-e tate and pro p ionate w ith som e bu ty rate an d lactate , H 2 , andCO 2. In batch cu ltu res bo th o ligo f ruc tose and inu lin spec if i-

cally s tim u late b if idobac te rial g row th (Figure 1) (7 , 1 4 , 2 3 ), ane f f ec t that h as been con f irm ed in bo th rats an d h um ans(1 4 , 24 , 25 ). In con trast, o ligo f ruc tose , inu lin , and starch in h ib itth e g row th o f C bo strid in . T he m echan ism f o r th is inh ib ition h asbeen tho ugh t to be re lated to low ering o f in te s tin al pH b yb if ido bac ten ial f e rm en tation . H ow ev er, G ib so n and W ang (26 )show ed that f ac to rs o ther than pH lead to rep ress ion o f th eg row th o f cbos tn id ial sp ec ie s. B if id obac ten ia are generally re -gard ed as b eing o f bene f it to health , hen ce the ir add ition toy o gurts in m any coun trie s . T he h ealth b en e f it is alleged lyre lated to stim u lation o f im m une f unc tion , v itam in B sy n thes is ,re sto ration o f a norm al f lo ra af te r an tib io tic the rapy , an d pre -v en tion o f g row th o f pathog en ic spec ie s. T h ey are the m ajo rf lo ra in breas t-f ed in f an ts and th is is one m ech an ism w herebythese ch ild ren are pro tec ted ag ain s t gu t in f ec tion s. Fruc to o li-go sacchan ides m ay also e f f ec t lip id m e tabo lism , decreas ingtrig ly ce ride and ch o les te ro l concen tration s in rats (19 ) and ind iabe tic hum an s (27 ) .

StarchesS tarch es are the m ajo r sto rag e po ly saccharide in m ost h ig her

p lan ts. T hey are a-g lucans and ex ist in tw o f o rm s: am y lopec -tin , w h ich is 70 -80% o f to tal s tarch , and am y lo se , w h ichusually com prises 20 -30% . A m y lop ectin s are larg e m o lecu le sm ade up o f > 10 00 0 g lucose re sidu es he ld tog ether b y a-1 ,4and a-1 ,6 lin k ag es in a branched tree -lik e struc tu re . A m y lo se isa sm alle r lin ear m o lecu le w ith on ly a-1 ,4 lin k ages . S tarch issto red in p lan ts as partially c ry stallin e g ran u le s, w h ich inam y lopec tin hav e c lu s te rs o f in te rchain bran ch ing p o in ts anddom ain s o f short ch ain s. T hese short chain s ex ist as do ub lehe lix es and g iv e rise to an alte rnating patte rn o f cry stallin e(array s o f doub le -s tranded he lix e s ) and am orp hous (z on es o fdense b ranch ing ) reg io ns (28 ). T h is p artially c ry s tallin e s tru c -

. FO S S tarchU Polydextrose

F IGURE 1 . B ac te rial coun ts (log1 0 ) f o r m ajo r genera o f h um an co lonaf te r 1 2 h in batch cu ltu re f e rm en te rs w ith e ith e r p o ly dex tro se , s tarch ,o ligo f ruc to se (FO S ), o r inu lin added . Ferm en te rs w ere inocu lated w ithm ix ed hum an f ecal bac te ria (5% w t:v ol). R esu lts are m ean s o f trip licated ete rm ination s in each o f th ree subje cts . From ref e ren ce 23.


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In tr insic fa cto r s . S tanch d ig estion is slow ed in the sm allin te s tin e if th e phy s ical f o rm o f the f oo d h in ders access o fpancreatic am y lase . T h is occurs if s tarch is co n tained w ith inw h o le o r p artly d isrup ted p lan t s truc tu re s su ch as grain s o rseeds ; if rig id ce ll w alls inh ib it sw e lling and d ispers io n o fstanch , as in legum es (3 0 , 32 ) ; on if stanch is v e ry denselypack ed in a f ood such as spagh etti (33 ). W hen the rate o f starchd igestion is decreased , p o stp ran d ial g lucose and in su lin re -spo nses are redu ced o n de lay ed . H eaton e t al (34 ) d em onstratedth at the se re spo nses are sm alle r if w heat, m aiz e , o r oats areg iv en as w ho le o r co arse ly g ro und grain s than if g iv en w h enf ine ly m illed . W hen h y dro ly s is is g ro ssly re tard ed , phy s icallyinaccess ib le starch m ay en ter the co lo n and be f e rm en ted , o r insom e cases , ap pear in f ece s (35 ).

S tarch gran u les that show x -ray d if f rac tio n pattern s B an d C( eg , in p o tatoes , bananas, and leg um es) are m ore re sis tan t topancreatic am y lase than are tho se o f patte rn A (in cereals) .U nge latin iz ed granu les o f the B f o rm m ay surv iv e coo k ingsuch as bak in g o f b iscu its. W hen starch g ran u le s are f u llyge latin iz ed and d ispersed , th e starch becom es eas ily d igestib le .H ow ev er, as th e ge l coo ls and ag es , th e po ly m ers on ce m oref o rm a partially c ry s tallin e struc tu re . R ecry s talliz ation or re t-ro gnadation depends on the f o rm ation o f in te rchain h y drog enbonds and occurs m ost rap id ly f o r the lin ear am y lo se . R e tno -g radatio n o f am y lopec tin is lim ited by its b ran ch ed stru ctu reand the po ly m ers o f re trograded am y lopec tin are le s s f irm lybound than are tho se o f re trograded am y lo se . R e trog nadeds tarch characte ris tically f o rm s the B -ty pe pattern .

O ther f acto rs in trin s ic to starchy f o ods that hav e been show nto af f ec t a-am y lase ac tiv ity in v itro inc lude am y lo se -lip idcom p lex es (36 ), nativ e a-am y lase inh ib ito rs (37 ), and N S Psw h ich m ay h av e a d irec t e f f e c t o n enz y m e activ ity (38 ).

E xtr insic fa cto rs . A lthoug h the e f f ec t o f in trin sic f ac to rs ond iges tio n o f s tarch y f oo ds m ay b e m easured in a repro duc ib lew ay , th is d oes n o t necessarily p red ic t ex ac tly the rate andex ten t o f d iges tio n o f the se f oo ds by ind iv idu als . T h is isbecau se eating ex po ses f oo d to v ariab le ex te rn al in f lu ences th atm ay alte r the su scep tib ility o f th e starch to hy dro ly s is bypan creatic am y lase . Fo r ex am p le , th e ex ten t o f chew in g de te r-m ines th e ph y sical access ib ility o f starch con tained w ith in rig ids truc tu re s (39 ). O ther f ac to rs are the trans it tim e o f thef o od f rom m ou th to term in al ileum (4 0 ), th e con cen tration o f

. . am y lase in the gu t, th e am ou n t o f s tarch p resen t, and theDiges tib i l ty presence o f o ther f oo d com po nen ts that m igh t re tard enz y m ic

hydro ly s i s .a tiv e s ta rc h g ra n u leA B or Ct yp e

( Pa rt ly c ry s t al li ne )

H e a t , m o i s t u r e

G e l a t i n i z e d( n o n - c r y s t a l l i n e )

Ra w

Io o k e d

Cooled

9 40S CUM M IN G S A N D EN G L Y S Ttun e has d is tin ct patte rn s on x -ray d if f rac tion . T hree m ain ty pesh av e been described : A , B , and C . T y pe A is thenm od y nam i-cally th e m ost s tab le f o rm and is f ound in cereal s tarches. T heB f o rm is charac te ristic o f banana, po tatoes, an d o ther tubersand the C pattern is f oun d in legum es . T he s iz e and cry stallin enatu re o f s tarch granu le s in f lu ence th eir su scep tib ility to pan -c reatic en z y m es . In g en eral, s tarch gran u les show ing x -rayd if f rac tion patte rn s B and C tend to be m ore re s is tan t topancreatic am y lase .S tarches are in so lub le in co ld w ate r bu t on heating th ey sw e lland ev en tu ally the ir m o lecu lar o rgan iz atio n break s dow n andlo se s its c ry s tallin ity (Figure 2 ). T he g ranu le is to tally d is -rup ted and at th is s tage the s tarch is read ily attack ed by en -z y m es . T he w ho le p rocess o f d is rup tion and sw e lling is k now nas g elatin iz ation (28 ) an d is the essence o f co ok ing starchyf oods . O n co o lin g , ge latin iz ed stanch recry s talliz e s, a ch an gek now n as ne trognadation . R e trograded s tan ch , particu larly am y -lo se , is m o re re s istan t to en z y m ic attack . T h e phy s ical de te r-m inan ts o f s tarch ge latin iz ation and recry stalliz atio n are com -p lex (28) bu t are o f v ital im po rtance fo r starch d ig estionb ecause ev en s im p le f ood processe s such as heating and coo l-ing , that occur during the p reparatio n o f a m eal w ill af f e c t th en u trition al quality o f starchy f oods .Sta rch d iges tio n

In the past d ecade tw o w id ely he ld assum ption s con cern ingth e d igestion o f stanch hav e b een d isp ro v ed . T he f irs t is that alls tarch , because it ex ists as large com p lex p o ly m ers, is hy dro -ly z ed and absorbed m ore slow ly than are s im p le sugars o rd isacch arid es. S ev eral stud ie s in v itro and in v iv o hav e show nthat th e phy s ical f o rm o f f oo d is the m ajo r de te rm inan t o f th erate o f d igestion o f bo th starches and sugars (29 , 30 ). T hesecond assum p tion is that starch is com p le tely hy dro ly z ed andabsorb ed w ith in the sm all in te s tin e. It is now k now n th at theex ten t o f starch d iges tion w ith in the sm all in te s tin e is v ariab leand that a subs tan tial am oun t o f starch , depend in g again onp hy s ical f o rm , escapes d igestion in the sm all in te stin e anden te rs the co lon (31 ). T he reason s f o r the incom p le te d iges tio no f starch m ay be separated in to in trin sic f ac to rs (ie, p ropertieso f th e f oo d ) an d ex trin sic f ac to rs (eg , chew in g and tran sitth ro ugh the b ow el).

S ta te o f f o o d P h y s ic a l s ta te o f s ta rc h

C o o l i n g an dh ig h m o is tu re

R e t r o g r a d e d( R e - c r y s t a l l iz e d )

B ( and C ) form

p a r t l y r e s i s ta n t

Iigestible

F I GUR E 2 . D ig est ib i lity o f starch in re lation to its phy sical f o rm andprocess ing .

C la ssi fica t io n a nd mea sur emen t of s ta r chesA class if icatio n o f starchy fo od s fon nu tritional p urposes that

is based on the in trin s ic f ac to rs af f ec tin g starch d ig estib ility isshow n in T ab le 2 . In v iew o f the im po rtan ce to health o f starchth ere is a need to hav e good laborato ry m e thod s f o r its m ea-su rem en t f o r bo th re search p urposes and f o r f ood tab les andlabe ling . A sing le v alue f o r to tal s tarch is o f lim ited usebecau se o f the w ide ly v ary ing d igestib ility o f d if f e ren t starchtypes .

T he v ariou s categorie s o f s tanch show n in T ab le 2 m ay bede te rm ined in the laborato ry by co n tro lled en z y m atic hy d ro -

P art ly ly s is an d m easurem en t o f th e re leased g lucose by us ingr e s i s t a n t g lucose ox idase. T o tal s tarch is m easured as th e g lucose

re leased by com p le te en z y m atic hy dro ly sis o f s tan ch af te rge latin iz ation in bo iling w ate r and treatm en t w ith p o tass ium


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EFFECTS O F FOOD CARBOHYDRATE IN TH E GUT 9415

1 RDS , rap id ly d ige ste d starch ; SD S , s low ly d ig ested sta rch ; RS , resistan t sta rch ; SD R I , starch d ig estion ra te index , eq u iv ale n t to RDS expressed as %o f to tal starc h ; RAG , rap id ly ava ilab le g lu cose, the sum o f free g lu co se, g luco se f rom suc rose, and g lucose f rom RD S.

TABL E 2C las sif icat ion of sta rch y foo ds b ased on sta rch d ig est ib i lity

Type o f s tarch(ex am ple of oc cur ren ce)

P ro bab le d ige stio n inth e sm all in test ine

R apid ly d ig estib le starch(f resh ly co oked starch y foo d) R ap id , co mp lete

S low ly d iges tib le s tarch(most raw ce reals) S low but com p lete

R es ista n t sta rchP hy sic all y in ac ce ss ib le

( jart ly m ille d grain s and seeds) R es ista n tR esistan t g ran ule s

(raw potato an d b anana) R es ista n tR etrog rad ed am y lose

(coo led , co oked po tato ,b read , and co rnflake s) R es ista n t

hydro x ide to d isperse re trograded am ylose . R ap id lyd igestib le sta rch and s low ly d igestib le s ta rch are m easuredafte r incuba tion w ith p an creatic am y lase and am ylog lucos i-dase a t 37 #{176}C . v alue fo r rap id ly d igestib le stanch is o b-tam ed as the g lucose released after 20 mm and slow lyd igestib le sta rch as the g lucose re leased afte r a fu rthe r 10 0mm incub a tion . R esis tan t s tarch is ca lcu la ted as the s ta rchno t h ydro lyzed af te r 1 20 mm incub ation . If requ ired , sepa-ra te va lues m ay be ob ta ined fo r p hys ica lly in accessib lesta rch (RS1), res istan t sta rch granu les (RS2), and retro gradedam ylo se (RS3) (31).

T able 3 show s va lues fo r rap id ly d ig estib le s tarch , slow lyd ig es tib le s ta rch , res is tan t sta rch , and to ta l s ta rch expressed as% dry m atte r fo r 18 sta rchy fo ods . T he to tal s ta rch con ten t o fthe fo ods ana ly zed ran ged from 19% in peas to 8 1% in w hitef lo u r. T he h ighest am oun t o f rap id ly d ig es tib le s ta rch w asfound in corn flakes. B reads and po ta to a lso con ta in ed su b-

s tan tia l am oun ts (56-7 1% ) of rap id ly d igestib le sta rch . T helow est va lues (3 -8% ) w ere fo und fo r banana flour , raw po ta tos tarch , an d han ico t beans . T he am ount o f slow ly d igestib les tarch is inversely re lated to the am oun t o f rap id ly d igestib les tarch and w as th ere fo re low for b reads and b reak fast ce rea lsand rela tive ly h ig h fo r fo ods such as spagh etti an d legum es inw hich the ph ysica l fo rm of the food in h ib its access o f pancre -a tic am ylase to the sta rch .

The p rod uc ts con ta in in g the m os t re sis tan t sta rch w ere rawpo ta to sta rch and banana f lo ur. T he la rge am ounts o f resis tan ts tarch in raw pota to stanch and banana flour re flec t the ir co n-ten t o f sta rch g ranu les w ith the B -type crysta l stru ctu re, w h ichis h igh ly resis tan t to pancrea tic am ylase. P o ta to b iscu its m adefrom 50% w hea t flou r and 50% pota to s tan ch a lso con ta ined asubs tan tia l am oun t o f RS2 , ind icating incom ple te g ela tin iza tionof sta rch granu les during bak ing . T he sm all am oun ts o f res is-tan t s ta rch in breads and breakfas t ce rea ls a re m ain ly re tro -g rad ed am ylose (RS3). T h e resis tan t s tanch fou nd in co ld p0-ta to , spagh etti, and leg um es is p ar tly R S3 and partly p hysica llyinaccess ib le s ta rch , R S1 . O f the comm on fo ods ana ly zed , har-ico t beans (soak ed overn igh t and bo iled 40 mm ) con ta ined them ost resis tan t s ta rch , w h ich cons titu ted 40% of the to ta l s tanchand com pr ised a ll th ree res istan t s tanch frac tions .

A m easure o f the re lativ e ra te o f stanch d igestion in a fo od isg iven by the s ta rch d igestion ra te in dex (SDR I).

SDR I = rap id ly d iges tib le sta rch /to ta l s ta rch X 10 0Th e h ighes t SD R I va lues (T ab le 3 ) w ere ob ta ined fo r b reak fas tce rea ls (93-95) an d breads (90 -93), ind ica ting effec tiv e ge la -tin iza tion of the s ta rch during h ea t p rocess in g . In com pariso n ,the SDR I v alue fo r raw w hite w h ea t f lo u r w as on ly 4 9 . T he ra teo f s ta rch d iges tion is co nside rab ly low er fo r co ld po tatoes thanfo r fresh ly coo ked po tato es. T he re la tive ly low SDR I va lues fo rspaghe tti and legum es reflec t the fac t th at the phys ica l fo rm of

TABL E 3V alues for d if feren t k in ds o f s tarch in fo ods

Fo odT ype of sta rch

SDR I RAGD S SDS R S T otal%bywt %bywt

W hite flo ur 4 0 39 2 81 49 45W h ite bread 6 9 7 1 77 90 42W ho le-m ea l bread 5 6 4 1 60 93 32Sp aghet ti, ho t 4 1 3 3 5 79 52 13D ige stiv e b iscu its 3 7 1 0 1 48 77 47Cornf lakes 7 3 2 3 78 94 81Sh red ded wheat 6 6 4 - 70 93 68Po rridge o ats 5 7 6 2 65 88 58Po tato , raw 2 7 70 79 2


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9425 CUMMING S AND ENGLYSTthese p roduc ts ren ders the s tarch partly inaccessib le to thed iges tive enzym es. In a s tu dy w ith 39 s tarch y foo ds, w e h av eshow n tha t the SDR I is h ig h ly correla ted w ith the g lycem icindex (41 ).

D uring the m easu rem en t o f rap id ly d ig es tib le sta rch andslow ly d iges tib le stanch , a va lu e is ob ta in ed fo r rap id ly ava il-ab le g lucose as the g lucose m easured after 20 mm in cuba tio nw ith p an crea tin , am ylog lu co sidase, and invertase (G 20).R ap id ly ava ilab le g lucose

= free g lucose + g lu co se from sucno se+ g lu co se re leased from sta rch w ith in 2 0 mm incuba tion

T he rap id ly av a ilab le g lucose v a lue thu s rep re sen ts the am oun to f g lu co se (in % by w t) th at can be expec ted to be rap id lyav ailab le fo r abso rp tion afte r a m ea l. R ap id ly av ailab le g lu -cose , expressed as a percen tag e of to ta l s ta rch p lus free sug ars,sh ow s a s ligh tly stron ger co rre lation w ith the g lycem ic indexth an do es the SDR I (41). S im ila r to the g lycem ic index , theSDR I re flec ts the ra te o f d igestio n of the stan ch (o r canb ohy -dra te) p resen t in the food bu t it does no t g ive any in fo rm ationab ou t the ac tua l am oun t o f g lucose like ly to be rap id ly av a il-ab le from the food . B ecau se rap id ly ava ilab le g lucose is ex -p ressed as % by w t on a w et-w eig h t basis , it g ives an easy-to -use gu id e fo r the am oun t o f g lucose rap id ly av ailab le fromdiffe ren t foo ds afte r con sum p tio n . R ap id ly ava ilab le g lucoseva lu es cou ld be used as a supp lem en t to the g lycem ic index andm ay be particu la rly use fu l to d iabe tic p atien ts and d ie titian s.T he fo ods in T ab le 3 sh ow a w id e range in the ir con ten t o frap id ly ava ilab le g lu cose . F or exam ple , the rap id ly av a ilab leg lucose in a 3 5-g portion of corn flakes (2 8 g g lucose) com e-spo nds w ith tha t in 68 g w hite b read , 88 g whole-m ea l b read ,175 g fresh ly coo ked po ta to , and 700 g han ico t beans (coo keda s d es cr ib ed ).

N on sta r ch p oly sa cch ar id esNSP s are p rinc ip a lly the po lysacch an ides o f the p lan t cell

w a ll and are no t a-g lucans. T hey in clud e ce llu lose and the

no nce llu los ic po ly sacchan ides pec tin and hem icellu lose . T heyare a d iverse g roup of m olecu les w ith vary ing degrees o f w ate rso lub ility , size , an d struc tu re (4 2). Severa l o the r n on-a -g lucanpo ly sacchan ides ex is t tha t a re ne ithe r s to rage nor ce ll w a llcon stitu en ts. T hese inc lude p lan t gum s and ex uda tes (gumarab ic ), seed m ucilages (ispaghu la ), bac ter ia l po ly saccharides( xan than), and syn th e tic com pounds such as po ly dex trose.

N SP can be m easu red by the E ng lys t m eth od , w hich h asbeen w ell docum ented e lsew here (43 -45 ) . A n in te rn atio na lco llab ora tiv e stud y com paring the E ng lys t m ethod fo r m easun-ing d ie ta ry fibe r w ith the P rosky (AOAC ) m eth od has re -cen tly been pub lished (46). A lthou gh th e d igestion of sta rchcan be d ifficu lt to p red ic t in v iv o , N SP s cons isten tly escaped iges tion in the sm all b ow el (47 -49). T h is in fo rm ation isderived princ ipa lly from the use o f ileos tom y pa tien ts as am ode l. A lthou gh ileo stom y pa tien ts hav e m any m ore bac te riain the te rm ina l ileum than do peop le w ith an in tac t gu t, it is stillpossib le to show , if p rop er ca rbo hydra te m ethodo lo gy is used ,th a t a ll the NSP s are recoverab le .

Physio logy and d iseasesThe phys io lo g ica l e ffec ts o f s tarch and NSPs in th e gu t

depend la rge ly o n the site , na te , and ex ten t to w hich they ared ig ested o r fe rm en ted . T h eir fa te in th e sm all bow el has a lreadybeen desc ribed . In the la rge in tes tin e all ca rboh ydra te is ava il-ab le fo r b reakdow n by the anaerob ic flo ra o f the co lo n , ap rocess known as fe rm en ta tio n , and th ro ugh th is p rocess exertsseve ral effe cts . Th is is a co n tin ual ly expand ing area o f resea rchan d is su bstan tia lly co vered in recen t bo oks and reports on thesub jec t (1 , 2 , 6 , 50-5 3). A summ ary of these e ffec ts is g iven inT ab le 4 .

The ro le o f NSP s in the sm all bow el is essen tially a p hys ica lo ne in wh ich th e p lan t ce ll w all ac ts as a barrie r to the releaseo f nu trien ts and so slow s the ir absorp tion . Th is is particu la rlyim po rtan t fo r sta rch d ig estion and fo r the co n tro l o f g lucosean d in su lin m etabo lism . T h is phenom enon has been known for20 y (54 ) an d led to the concep t o f the g lycem ic index offoods (55, 56 ) an d to m ajo r changes in the m anagem ent o f

T A B L E 4Pro per ties of sta rch an d nonstarch p oly sa cch arid e (N SP ) in the gut

R egion and pro per ties P hy sio log y Di se a se sS tom ach , sm all bow e l

NS PG ene ral p hys ica l effects Inc rea sed sat ie ty Obesi tyA s ce ll w all R ed uced rate o f starc h b reakd ow n and gluco se absorp tio n DiabetesA s ge l R educed choleste ro l , b ile ac id absorp tio n C orona ry he art d isea se , gal lsto ne s

S t a r c hR esis tan ce to pancreat ic am y lase inphy sic al fo rm , granu le typ e, an drecrysta l l ized R educed rate an d ex ten t o f g lucose abso rp t ion Diabetes

Larg e bow elA l l c ar bo h yd ra te

If p hy sica l fo rm reta ined(cell w all m ain ly) Increased sto o l bu lk Const ipat ion

If ferm en ted (sho rt-cha in fatty ac ids ) Absorbed -#{247} en ergy , s tim ula te N a /H 2O ab so rp tion Diar rheaH2C02

B acte ria l g row th

G row th o f ep i the lium , b u ty rate-ce ll d if fere n tia tio n ,hy dro gen dispo sal to CH 4, SH , or CH3COOH

B ac teria l p ro te in sy n th esis an d b iom assC an cer , p o ly psCarcinogenesis (?)


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EFFEC TS OF FOOD CARBOHYDRATE IN THE GUT 943Sdiab e tes . S tarch h as little in fluence on d ig es tio n and absorp tionof o ther nu trien ts in the sm all b ow el. R es istan t sta rch is m ain lyinso lub le and lacks bo th the ge l-fo rm in g or su rface effec ts o fNSPs . B y con trast N SPs have c lea r ef fects on cho leste ro lab sorp tio n (57 ) an d th roug h the ir ab ility to inc rease b ile ac idex cre tion an d redu ce d eo xycho la te fo rm ation m ay he lp p reven tga llstones (58 ).

In the la rge b ow el energy is sa lvaged from und iges ted car-boh ydra tes th ro ugh fe rm en ta tio n . T he m icrob io lo gy , phy sio l-ogy , and im portance fo r d isease of fe rm en tation have beenrecen tly rev iew ed (59 ). T he princ ipa l p roduc ts o f fe rm en ta tio n ,the sh ort-cha in fa tty ac ids , p ro v ide an energy sou rce fo r hu-m an s and have im po rtan t e ffec ts o n the co lon ic ep ithe lium ,w hich m ay be a m ajo r p ro tec tive fac to r aga inst la rge b ow elcancer (60). In th is co n tex t s tarch m ay be m ore s ign ifican t th anNSPs (61).

D iet a r y r ecom m en d a t io n s f o r st a r ch an d N S PThe recomm enda tio n fo r coun tries w ith W este rn -sty le d i-

ets to inc rease th e ir in take of s ta rch and NSP s [som etim esre fe rred to as com plex carb ohydrates (2 )] has becom e un i-versal s ince it w as first sug gested by the U S Sen ate S e lec tC omm ittee on N utrition and H um an N eeds (62). Q u an tita -tive recomm enda tions fo r s ta rch and NSP in takes d er iv edfrom the W orld H ea lth O rgan iza tio n (W HO ) (63) and theUK D ep artm en t o f H ea lth (64) are as fo llow s: fo r s ta rch asa p ercen t o f to ta l fo od en ergy (exc lud ing a lco ho l), 5 0 -70%(W H O ) and 24% (UK , popu la tion av erag e tha t assum es tha tin tr in sic and m ilk su gar con tribu te 20% of foo d energ y), andfo r N SP s, 16-2 4 g/ d ( W H O ) and 18 g/ d (U K , ran ge = 12-24g / d ). N ote the m ark ed d if feren ces in recomm enda tions fo rsta rch be tw een the tw o reports .

StarchL im its fo r s tarch in take have u sua lly been se t by defau lt, ie,

sta rch is con side red to be an energy fille r in the d ie t on ce lim itshave been se t fo r fat an d pro te in . T he W HO report is typ ica l inth is respec t say ing th a t the recomm enda tions accou n t fo r25-45% of the to tal energy in take as fa t and p ro te in . S ince theG ro up does no t recomm end tha t a lco ho l be in gested , it fo llow sth at the rem ain ing energ y in take w ill be prov ided by carboh y-d ra te, fo r w hich the low er and upp er lim its fo r the popu la tionnu trien t goa ls a re the re fo re se t a t 55% and 75% . The G roupsaw spec ific ad van tages assoc ia ted w ith the in take o f com plexcarb ohyd ra tes and has propo sed a low er lim it fo r th is c lass(50% of energy) (63 ).

T h e UK die tary referen ce v alues repor t to ok a s im ila rap proach , a lth ough in d iscu ss io n the possib le sp ecific ad -van tages of s ta rch w ere deba ted ex tensive ly : Th e Pane lth erefo re p ro posed tha t sta rches and in trins ic and m ilk sug-ars shou ld pro v ide the ba lance of d ie ta ry energ y n o t p ro -v ided by a lcoh o l, p ro te in , fa t and nonm ilk ex tr in sic sugars ,th at is on average 37[% ] o f to ta l d ie ta ry energy fo r thepopu la tion (6 4).

W hat m igh t be the spec ific ad van tages of consum ing sta rch?1) S tarch as a sub stitu te fo r sa tu ra ted fa t w ill lead to low er

b lo od c ho le ste ro l.2) Sta rch ra the r than sugar sho u ld low er the risk of den ta l

ca r ies .

3 ) S ta rchy food s, nam ely cerea ls, p u lses , and v eg etab les,co n tain a w ide variety of m icron u tn ien ts tha t su gary and fa ttyfoods usua lly do no t.

4 ) S ta rchy foo ds are p re fe rab le to a lcoho l as a source ofenergy .

5) S ta rchy food s ra the r than fatty and sugary foods m igh tlim it the risk o f obes ity .

6) S om e s ta rch is resis tan t to d iges tio n b y pan crea tic am ylasean d m ay con trib u te to the prev en tio n of b ow el cancer.

7) The typ e o f sta rchy food is a m ajo r con tro lling fac to r fo rb lood g lucose and insu lin concen tra tio ns.

T he ev idence fo r these sta tem en ts is con ta ined in recen trep orts on th is top ic . A lth ough none of it is u nequ ivoca l, fewp eop le in teres ted in pu b lic hea lth po licy w ould no t ag ree tha tth is is p ruden t adv ice to the genera l po pu la tio n .

Nonstarch polysaccha ridesNSP s are new com ers to d ie ta ry recomm enda tions . S evera l

n a tion al b od ies have now m ade quan tita tive recomm enda tio nsfo r in c reases in d ieta ry f ib er in take bu t because of the lack o fan agreed defin ition of fibe r and of a m ethod fo r m easuring it,th ese recomm enda tions do no t c ro ss in te rna tiona l bou ndariesvery w ell. T here fo re th e B ritish N utrition F ound a tion , W HO ,an d th e UK Departm en t o f H ea lth have op ted fo r N SPs as thebest in dex o f fib e r. D ie ta ry NSPs have been shown to have aw ide varie ty of p hys io lo g ica l ef fec ts , pa rticu la rly o n d ig estionan d are inc lud ed in th e e tio logy o f d iseases su ch as bow elcan cer, d ive rticu la r d isease , d iabe tes , obesity , co ronary heartd isease , an d ga lls tones. H ow ever, it is c lea r th at the ev id ence inrela tion to m os t o f these cond itions is n o t su fficien t to a llow aquan tita tive estim ate o f need fo r the po pu la tion to be m ade .R a th er, th e ev iden ce po in ts to the goa l o f a d ie t characte rizedby h igh N SP (an d s tarch ) in takes.

T he ro le o f N SP is m uch m ore c lear ly defined w ith re fe renceto bow el hab it. T he argum ents fo r a recomm ended d ie ta ryam oun t the re fo re run as fo llow s:

1 ) NSP s increase stoo l ou tpu t in a dose-re lated fash io n u p to 32 g/ d ( 65 ) .

2 ) N o other d ie ta ry com ponen t so affec ts bow el h ab it a l-th ough res is tan t s ta rch is laxa tive and m ay con tribu te to feca lb u lk ing in h ig h-s ta rch , h igh-NSP die ts (66).

3 ) Constipa tion is a frequ en t p rob lem in the U nited K in gdomand the Un ited S ta tes, w ith a lm o st ha lf the popu la tion hav ings too l w eig h ts < 100 g/ d (65 , 67) .

4 ) In ep idem io log ica l s tud ies, s too l w eig h ts < 1 50 g/ d ar easso cia ted w ith inc reased r isk o f b ow el cancer, d ive rticu land isease , and h ig h deo xycho la te concen tra tio ns in b ile (6 7).

5 ) NSP in tak es shou ld be increased to change average stoo lw eigh t b y =25% . This m ean s tha t N SP in takes shou ld in creasef rom 13 to 18 g /d . U

Re f e r e n c e s1 . K r itchevsky D , B onfie ld C , A nderso n JW , ed s. D ie ta ry fibe r. C hem -

istry , phy sio logy an d h ealth e ffec ts. N ew Y ork : P lenum P ress , 1990 .2 . B r itish N utr itio n Found ation . C om plex ca rbo hyd rates in foo ds. R ep or t

o f the B ri tish N utri tion Foundations T ask F orc e. London: Ch apm an &H all, 1 990 .

3 . Engly st H N , Q u ig ley M E , H udso n G J . D eterm ina tio n of d ieta ry f ib reas no n-s tarch p oly sac cha rid es w ith ga s-liqu id chrom a tog rap h ic , h ig h-


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944S CUMM ING S AND ENGLY STpe rform ance liq u id chrom a tog rap h ic o r co lo rim etr ic m easu rem en t ofco nsti tuen t sug ars. A n aly st 199 4;1 19 :14 97 -50 9 .

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