Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: A comprehensive food frequency questionnaire (FFQ) was developed to assess the daily total
flavonoid intake over the past fortnight within a 14-week intervention that consisted of four periods
to determine the effect of rooibos consumption on oxidative stress in adults (n=40) at intermediate
to high coronary heart disease (CHD) risk. Within the intervention the comprehensive FFQ validity
(against six estimated dietary records and biomarkers), reproducibility (on administrations in the
washout and control periods six weeks apart as these periods had similar flavonoid intake
restrictions) and responsiveness (across the four intervention periods of changed dietary
conditions) was evaluated. The baseline period dietary record and FFQ dietary sources found to
contribute most to the participants’ daily total flavonoid intake, considering the percentage
contribution, and the between-person variation in intake, considering the stepwise multiple
regression analysis, formed the food list of the resultant abbreviated FFQ. The validity,
reproducibility and responsiveness of the latter were also evaluated within the intervention and its
validity (against dietary records) and reproducibility (on re-administration two weeks apart) in an
additional group (n=90) being at low and intermediate CHD risk to evaluate its external strength.
The validity and reproducibility evaluations of the comprehensive and abbreviated FFQs in the
intervention and abbreviated FFQ within the additional group comprised paired difference tests (to
establish the ability to estimate group intakes), correlation coefficients (to establish the ability to
rank individual participants), category agreement and gross misclassification next to the weighted
kappa statistic (to establish the ability to classify the participants into tertiles and quintiles of intake)
and Bland-Altman plots (as representation of the limits of agreement between the two dietary
assessment methods). Correlation coefficients were also used for biomarker validity evaluations in
the baseline period. The repeated measures analysis of variance (ANOVA) (Bonferroni correction)
was used for the responsiveness evaluations of the comprehensive and abbreviated FFQs across
the intervention periods alongside that of the biomarkers as evidence for the changed dietary
conditions.
The study demonstrated that the comprehensive FFQ could be modified to a format with a brief
food list as few items contributed appreciably to the total flavonoid intake and of which most also
contributed to the between-person intake variability. The comprehensive and moreover the
abbreviated FFQ in the validity evaluations provided sufficiently accurate daily total flavonoid intake
estimates. They could determine the intake at group level in correspondence with that of the
dietary records. The participant intakes could additionally be categorized and in particular ranked
greatly alike to the dietary record intakes. The Bland-Altman plots revealed proportional bias
regarding overestimation at the higher intake level. The reproducibility also appeared to be greatly
satisfactory although seasonal fruit exclusions from the abbreviated FFQ food list may hamper its
repeated administration. Both FFQs also confirmed the changed total flavonoid intakes across the
intervention periods in relation to changes in the expected direction concerning the plasma total
polyphenol, conjugated diene and thiobarbituric acid reactive substance concentrations. / AFRIKAANSE OPSOMMING: ‘n Omvattende voedsel frekwensie vraelys (VFV) is ontwikkel om die daaglikse totale flavonoïed
inname oor twee agtereenvolgende weke te beraam te midde van ‘n 14-week intervensie. Die
intervensie het uit vier periodes bestaan wat die effek van rooibosinname op oksidatiewe stres in
volwassenes (n=40), met ‘n intermediêre tot hoë koronêre hartsiekte (KHS) risiko, bepaal het.
Binne die intervensie is die geldigheid (teen ses geskatte dieetrekords en biochemiese merkers),
herhaalbaarheid (op aanwending ses weke uitmekaar in die uitwas en kontrole intervensie
periodes met dieselfde flavonoïed inname bepalings) en waarneembaarheid (oor vier intervensie
periodes van veranderde dieet bepalings) van die omvattende VFV geëvalueer. Die dieetbronne in
die basislyn periode dieetrekords en vraelyste wat die meeste tot die deelnemers se daaglikse
totale flavonoïed inname (baseer op die persentasie bydrae) en die tussen-persoon variasie in
inname (baseer op die stapsgewyse meervuldige regressie analise) bygedra het, het die
voedsellys van die voortvloeiende verkorte VFV gevorm. Die geldigheid, herhaalbaarheid en
waarneembaarheid van dié VFV is binne die intervensie geëvalueer en die geldigheid (teen
dieetrekords) en herhaalbaarheid (heradministrasie twee weke later) daarvan in ‘n verdere groep
(n=90) met lae en intermediêre KHS risiko as evaluasie van die eksterne vermoë van die VFV.
Die geldigheid en herhaalbaarheid evaluasies van die omvattende en verkorte VFV in die
intervensie en die verkorte VFV in die verdere groep het bestaan uit gepaarde verskil toetse
(bepaling van die groepinname skattingsvermoë), korrelasie koëffisiënte (bepaling van individuele
deelnemer rangorde skattingsvermoë), kategorie ooreenstemming en erge wanklassifikasie naas
die aangepaste kappa statistiek (bepaling van die vermoë om die deelnemer innames in derdes en
vyfdes te klassifiseer) en die Bland-Altman karterings (verteenwoordiging van
ooreenstemmingslimiete tussen die twee dieetinname metodes). Korrelasie koëffisiënte is ook
gebruik vir biochemiese merker geldigheid evaluasies in die basislyn periode. Die herhaalde
metings analise van variansie (ANOVA) (Bonferroni regstelling) is gebruik om die
waarneembaarheid evaluasies van die omvattende en verkorte VFV oor die intervensie periodes
naas dit van die biochemiese merkers te evalueer as bewys van die veranderde dieet bepalings.
Die studie het aangedui dat die omvattende VFV gewysig kon word tot ‘n formaat met ‘n verkorte
voedsellys omdat slegs ‘n aantal items merkbaar tot die totale flavonoïed inname bygedra het en
die meeste hiervan ook tot die tussen-persoon variasie in inname. Die omvattende en die verkorte
VFV het in die geldigheid evaluasies daarvan voldoende akkurate daaglikse totale flavonoïed
inname skattings opgelewer omdat groep innames bepaal kon word in ooreenstemming met dit
verkry van die dieetrekords en die deelnemer innames bykomend kategoriseer en in besonder
grootliks eenders rangeer kon word as met hul dieetrekord innames. ‘n Proporsionele oorskatting
by die hoër inname vlakke is wel vir al twee getoon in die Bland-Altman karterings. Die
herhaalbaarheid was ook grootliks aanvaarbaar, alhoewel seisoenale vrugte uitsluitings in die
verkorte VFV voedsellys die heruitvoering kan bemoeilik. Al twee vraelyste kon ook die
veranderinge in die daaglikse totale flavonoïed inname oor die intervensie periodes bevestig in
ooreenstemming met veranderinge in die verwagte rigting van die plasma totale polifenool,
konjugaat diëne en tiobarbituursuur reaktiewe stof konsentrasies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80019 |
| Date | 03 1900 |
| Creators | Venter, Irma |
| Contributors | Marnewick, Jeanine L., Herselman, Marietjie G., Nel, Daan G., Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Interdisciplinary Health Sciences. Human Nutrition. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 474 p. |
| Rights | Stellenbosch University |
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