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494 LETTER S TO THE ED ITO Ru la tio ns u nque s tion ab ly a re far too h igh .C h ild ren w ho w ere s tud ied in Iow a in 1 962w e re ex trao rd ina rily av id con sum ers (6 ). S ow e re som e of the Jew ish ch ild ren w hom w eh av e been study in g in Jo hann e sb u rg (7 ).S uch co u ld h ard ly fa il to bene fit from m a jo rd ecrease s in sug ar in take . T h is , h ow ev er,d oe s n o t im p ly accep tan ce tha t c arie s s itua -t ion s w ill d ram a tic ally im p rove o nce sug arin take fa lls . N o r d oe s it im p ly su pport fo r con tro l o f su ga r b y p rice p o licy as pu tfo rw ard by H ow arth (8 ), n o r fo r go ve rn -m en t hea lth w a rn in gs on sug ar and h ighsu ga r foo ds , s im ila r to tho se on cig a re ttep ack ag es (9 ).

A s D rs H acke tt and R ugg -G unn so rig h tlyaffirm , ca rie s is a com plex d ise ase o f m u lti-fa c to ria l o rig in . T h e gu id ing p rinc ip le o fco n tro l cou ld w ell b e o ne o f d ie ta ry m od er-a t ion , p e rh aps bo rde ring o n ab stem iou sne ss.It is in tere s ting th at th is is w ha t w as cou n-seled b y S ir R ich ard D o ll( 1 0) in h is H a r-v e ian O ra tio n on P rospec ts fo r P reven -tio n . In the com ba ting o f a w ide sp ec trumof deg en era tiv e d iso rd ers an d d ise ase s h ed esc ribed a d ie t w h ich h ad m o st o f th e cha r-ac te ris tic s o f th e w art im e d ie t re fe rred to , a shav ing th e m o st sc ien tif ic ba s is .

ARP W a lke r, D S c

Sou th A fric an Ins ti tu te fo r M ed ica lRes ea rch

POBox 1038J ohanne sbu rgSou th A fric a , 2 00 0References1 . W a lke r A RP . S uga r and den ta l de ca y . L an ce t

1983 ; l :599 .Ia . T a keu ch i M . E p idem io log ic a l s tud y on re la tion

be tw een den ta l ca ries inc id en ce and sugar co n -sum ption . B u ll T o kyo D en t C o il 1 9 60 ; 1 : 5 8 -7 0 .

2 . N ew b run E . S ugar a nd den ta l ca ries . A re v iew o fh um an s tud ie s . S cie nce 1982 ;2 17 :4 18 -2 3 .

3 . S he ih am A . S ugars a nd den ta l de ca y . L an ce tl98 3 ;l :28 2 -4 .

4 . B rad fo rd EW , C ra bb HS . C a rb oh yd ra te res tric tio nand ca ries in c id en ce . B r D en t J l9 6 l;l I 1 :2 73 -7 .

5 . A inam o J, Ho lmbe rg SM . The ora l h ea lth o f ch il-d re n o fde n tis ts . S cand J D en t R e s l9 74 ;82 :54 7 -9 .

6 . H odges R E , K reh l W A . N u tr it io na l s ta tus o f tee n -age rs in Iow a . Am J C lin N utr 19 65 ;1 7 :2 00 -lO .7 . W a lk e r A RP , D is on E , W a lk e r BF , Jo ne s J , W a lk e r

C , Sega l A . Low den ta l ca rie s in Jew ish ado le scen ts choo l p u p ils in S ou th A frica . J D en t C h ild1983;2l9-24.

8 . H ow arth D P . S uga r ava ilab il ity , su ga r con sum p -tion and den ta l ca rie s . M Sc the s is . U n ive rs ity o fL ondon , 1982 .

9 . S he ih am A . E du ca ting the pub lic a b ou t suga r. JD en t R es 1 98 0;5 9(D II):2 20 3-9 .

10 . Doll R . P rospe c ts fo r p rev en tio n . T he Ha rve ia no ra tio n o f 1 982 . L ondon : R o ya l C o lle ge o f P h ys i-c ia n s , 19 82 .

The use o f h ea rt ra te to m easu re hab itua l ene rgy expend itu reD ea r S ir:

I re ad w ith in te re st th e a rtic le by C h ris -tenssen e t a l (1 ) and w as ra th er su rp rised tosee tha t a t th is s tage th ey sh ou ld be exp ress -ing su rp rise o ve r th e lim ita tio ns o fthe heartra te (H R )/en erg y exp en d itu re (EE ) reg res-s io n line to es tim a te da ily en erg y ex pend i-tu re .

M ore th an 3 0 y r ag o L undgren (2 ) d em -o ns tra ted th at th e re la tio nsh ip be tw een H Rand EE va ried d u rin g th e day and a t anyone tim e w as su b je c t to a la rg e num ber o fex tran eo us fa c to rs . T h e m e tho d used byC h ris tensen et a l (1 ) to d eriv e the ir reg re s-s io n lin es from m easu rem en ts o f ly ing , s it-t ing , and cyc ling w ill c erta in ly g iv e a h ig hco rre la tio n co e ffic ien t fo r H R and EE bu tthe p red ic tio n o fEE from H R usin g a reg re s-s io n lin e so d e rived is v alid fo r p red ic ting

EE on ly ifth e sub je ct re stric ts h im se lfto th eac tiv i tie s o f ly in g , s itt ing , an d cyc lin g . In19 60 w hen B ooy en s an d H e rvey (3 ) no tedtha t the re la tion sh ip be tw een H R and EEappeared to co ns is t o ftw o line s-on e a t lowleve ls o f EE and one a t h igh e r leve ls -theys ta ted tha t if EE w ere to be p red ic ted fromH R . the ac tiv itie s used to d eriv e the reg re s-s io n lin e sho u ld b e the sam e as tho se thesub je ct w ou ld b e engag ed in w hen h is EEw as b eing m easu red (p red ic ted ). D aunceyand Jam es (4 ) have co n firm ed th is o ve rsho rt-te rm m easu rem en ts o f H R and heatp rodu c tion in a ca lo rim e ter. T h ey sh ow edtha t the re la tion sh ip b etw een H R and EE atthe low e r in tens ities o f EE w as cu rv ilin ea rn o t re ct ilin ea r. T h is h a s also been sh ow n byV ite ri e t a l (5 ). C om pa rin g EE figu res ob -tam ed from H R /EE reg re ss io n lin es w ith EEd educed from m easu rem en ts o f food in take

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and changes in body fat m easured over 6 to12 m onths, A cheson et al (6) show ed thatthe best predictor of EE from H R used thelog of EE, the regression line being derivedfrom m easurem ents of H R and EE w ith thesubject going about his norm al business. Theuse of the log value took account of thecurvilinear relationship at the low er inten-sities of exercise already referred to. U sing astraight linear regression derived from lying,sitting, and stepping m easurem ents overes-tim ated EE by a m ean of 25% for the groupbut w ith individual errors varying betw een6 and 42%.

Figure 1 show s sim ultaneous m easure-m ents of H R and EE m ade on one subjectat different tim es over a 7 m onth periodusing the techniques described previously(6). The stepping m easurem ent w as m adew hile he stepped on and off a 9-inch step 6,12, and 24 tim es/m m and the m ixed activityme a s u r e me n t s we r e ma d e o v e r 4 5 - mm p e -

riods w hile he w ent about his everyday busi-ness. The lying m easurem ents w ere m adefirst thing in the m orning before he got outof bed. R egression line A is derived fromlying, sitting, and stepping m easurem entsand regression line B from m ixed activitym easurem ents w hen EE w as4.5 kcal/m in.R egression C is derived from the sam e dataas B but uses the logarithm ofEE . The m ixedactivity points from w hich B and C arederived are lim ited to those points w hen EE

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49 6 LETTERS TO THE ED ITO R

of co va riance; p< 0 .00 1 ) as is th e slop e(an a lys is o f va rian ce; p 0 .0 00 1). In o the rw ord s d iffe ren t ac tiv itie s g ive rise to d iffe ren treg re ss io n lin e s. It is v e ry easy to con s truc ta reg re ssion line w ith a h igh ly s ign ific an tco rre la tion coe ffic ien t if the sub jec t eng ag esin o n ly o ne activ ity a t d iffe ren t in tens itie s .T o co ns tru ct a reg re ss ion lin e w h ile the su b -je c t g oe s ab ou t h is no rm a l bu sine ss is h ard erb ecau se the leve l o f E E is l ike ly to b e le ssan d th e po in ts sc attered m ore w id e ly ab ou tthe lin e , bu t if a reg re ssion lin e o f th is so rtis to b e u sed to p red ic t EE from H R th is isthe m ost lo g ica l w ay of d o in g it.

I T Campbel l , M D , FFARCSU nive rsi ty D ep artm en t o f A n ae s the s iaR oya l L iv erp oo l H o sp ita lL iv e rp oo l, E ng lan d

R eply to letter b y C am pb ell

D ea r S ir:I t is ha rd ly co rre ct tha t th e au th o rs (1 )

exp ress su rp rise ov er the lim ita tio ns o f theheart ra te /ene rgy exp en d itu re reg re ss io n lineto e s tim ate d aily ene rgy exp en d itu re . A sC am pbe ll p o in ts o u t in h is le tte r , th e p he -nom enon is w ell k now n and unde rstoo d byse ve ral p hy sio lo gis ts .

W e be lieved , how ev er, th a t the ex tens iv eu se o f th ese co n tro ve rs ia l cu rve s , ev en inre cen t repo rts (2 , 3 ) ju s tif ied th e de scrip tio no f the sho rtcom ings o f th e m e tho d . O ura rtic le (1 ), w e be lieve , p o in ts o u t th e p oo rre liab il ity even w hen cu rv es are gene ra tedo n th e ba s is o f h om ogenous activ ity . N a rrowconfid en ce lim its o f reg re ssion line s gene r-a ted on d iffe ren t occas io ns do no t secu rere liab le p red ic tion o f ca lo ric exp en d itu re .

Re f e r e n c e s1 . C hristenssen CC , F rey HMM , Foenste lie n E ,

Aadland E , R e fse im HE . A critica l eva lua tion ofene rgy expenditure estima te s base on individua l 02consumption hea rt ra te curves and average da ilyheart ra te . Am J C lin N utr 19 83 ;37 :46 8 -72 .

2 . Lundgren NP V . Physiologica l e ffe cts oftime sched-ule work on lumber workers. Acta Physiol S cand1 94 7;1 3(sup pl 4 1):l-1 3l.

3 . Booyens J, H e rvey G R . The pulse ra te as a meansof measuring me tabolic ra te in man. C an JBiochem Physiol l9 60 ;38 : 1 30 1 -9 .

4 . D auncey M J, James W PT . Assessment ofthe hea rtra te me thod for de te rm ining ene rgy expenditure inman using a whole body ca lorimete r. Br J N utrl9 79 ;42 : 1 -1 3 .

5 . V ite ri FE , Torun B, G a licia JC , H erre ra E . D ete r-m ining ene rgy costs of agricultura l activities byre spirome te r and energy ba lance te chniques. Am JC li n N ut r 1 97 l; 24 :1 41 8-3 0.

6 . Acheson KJ, C ampbe ll IT , E dholm 00 , e t a l. T hemeasurement of da ily energy expenditure -aneva lua tion of some te chniques. Am J C lin N utrl 9 8 0 ; 33 : l 1 5 5 - 64 .

C C hr C hristensen, M DIn s ti tu te fo r R esp ira to ry P hys io lo gyU llevaa l H osp ita lO slo , N o rw ay

Re f e r e n c e s1 . C hristensen CC , F re y HMM , Foenste lie n E , Aad-

land E , R e fsum H . A critica l e va lua tion of ene rgyexpenditure e stim ate s based on individua l 0 2 con-sumption/heart ra te curves and ave rage da ily heartra te . Am J C lin N utr 1 983 ;3 7 :4 6 8 -7 2 .

2 . W arnold I, Lenner RA . E va lua tion ofthe hea rt ra tem ethod to de te rm ine the da ily ene rgy expenditurein dise ase . A study in juvenile diabe tics. Am J C linNutr l977;30:304- 15.

3 . W arnold I, C a rlgren G , Krotkiewski M . Ene rgyexpenditure and body composition during we ightreduction in hype rplastic obese women. Am J C linN utr 1 97 8;3 1:7 50 -6 3.

S eru m ch o lesterol resp o nse to d ietary ch an g eD ea r S ir: cho les te ro l-free d ie ts th a t are id en tic a l ex -

cep t fo r fa tty ac id com positio n . F ats p ro -R ecen tly , B eck er e t a l (1 ) repo rted m ean v ided 4 0% o f to ta l ca lo ries in all th re e d ie ts

serum cho le s te ro l v alue s o f 1 2 m en on th ree an d from th e ir T ab le 2 the p ercen tage s o f