however 
 none of them are considered of excellent performance to accurately determine what is 
 ingested for all age groups . even in studies based on a " gold 
 standard " method as food weighing , there can be deviations in the estimation of some 
 items .
the r24h is among the most widely used instruments for assessing the accuracy of 
 selfreport measures .
it is considered a fast and financially accessible tool that can 
 reflect the individual 's diet when applied repetitively .
this repetitive evaluation is important because 
 deviations can be found in the estimates produced by self - report measures .
studies involving parents of children or adults showed that the estimates of food intake 
 are considerably underestimated for the unhealthy foods and overestimated for the 
 healthy ones .
moreover , estimates for children and adolescents can be 
 affected by the recall bias .
they have problems in correlating the frequency of food 
 intake and the time of ingestion , and sometimes they also tend to remember just the 
 preferred foods . children and adolescents frequently have difficulties in reporting the size of the 
 consumed portion .
this fact is often associated with cognitive constraints , a little 
 explored subject in the literature .
it is known that in children 7 - 8 years of age , there is an increased ability to 
 participate in evaluations such as diet recall without the help of parents .
these difficulties in associating items of diet with time are 
 reported as an information overload , since many times the child does not have a clear 
 memory of past events .
thus , it is necessary to reconstruct the events by making 
 inferences from what they usually ingest .
this inference many times is n't what the child 
 ingested , but can portray a usual diet . on the other hand ,
the period of adolescence is characterized by 
 intense changes of physical , psychological and social context , and cognitive ability and 
 level of emotional maturity may be variable in this period .
most of the studies for validating food frequency questionnaires are concerned about 
 investigating the nutritional composition of the diet and the intake amount of calories 
 and nutrients ( macro or micro ) .
however , fast 
 and specific tools for estimating food behaviors , such as the frequency of carbohydrate 
 intake with and without sugar , are scarce .
this frequency is the main etiologic factor for dental 
 caries , a chronic disease 
 considered a serious public health problem .
thus the objective of this study was to compare estimates of food behavior related to 
 oral health produced by a self - report measure and dietary recalls of 24 hours .
a cross - sectional study was conducted among adolescents attending public schools in 
 piracicaba ( 0.7 ppm f in tap water ) , 157 km from the capital of so paulo - brazil , with 
 an area of 1,377 km and a population of 364,571 people .
the study was approved by the research ethics committee of public 
 health school - usp ( protocol no .
the study population was selected from the representative sample of 483 adolescents that 
 participated in the study " determinant factors of the risk of obesity in adolescents 
 from public schools of piracicaba : cross - sectional study as a first step in a cohort 
 study " supported by fapesp ( so paulo research foundation ) , process no .
nutritionists trained under the supervision of the department of nutrition from the 
 public health school at the university of so paulo applied three 24 hours dietary 
 recalls ( r24h ) .
the dietary recalls were administered at nonconsecutive days to cover 
 a day in the weekend , setting up 15-day intervals between them .
the self - report instrument had 
 three questions for each one of the eleven food items .
the questions were about food 
 intake related to oral health , as well as frequency and the time of the day in which 
 the food was ingested .
finally , we compared this instrument to the dietary recalls 
 ( r24h ) . the tools ( self - report measure and r24h )
were tested in a pilot study and adjusted 
 accordingly before being used in the feld .
the nutritionists used utensils such 
 as cups , plates , and spoons to apply r24h . to examine the food behavior related to oral health in the past 15 days , the eleven 
 investigated items were ice cream , fruits , chocolate , soft drinks , vegetables , juices 
 with added sugar , biscuits ( with and without filling ) , greens , chocolate milk , and 
 sweets ( chewing gum , candy ) .
these items were selected based on the results of a 
 previous study on food intake conducted in piracicaba - sp , using data related to the intake average obtained 
 from two 24-hour recalls ( r24h ) applied in 93 adolescents .
the food items were chosen 
 taking into account the content of sucrose , the frequency of consumption and the 
 number of adolescents who reported the food intake .
data from food frequency were collected in six categories : 1 to 3 times in the last 
 15 days ; 4 to 6 times in the last 15 days ; 1 time a day ; 2 times a day ; 3 times a 
 day ; 4 or more times a day .
time of the day related to the food ingestion was 
 registered according to three categories : at mealtime ( breakfast , lunch or dinner ) , 
 at another moment ( mid - morning or mid - afternoon or evening before bedtime ) or both . 

items such as vegetables , greens and fruits were included based on questionnaires 
 from who ( 2010 ) and cdc about diet , due to the importance these foods in relation to 
 oral health - related behavior .
the measures of body weight and height of the adolescents were performed using a 
 digital scale with a capacity of 150 kg , sensitivity of 100 grams ( tanita , solar 
 digital scale hs 302 , tokyo , japan ) , and a portable estadiometer ( seca bodymeter 208 , 
 hamburg , germany ) .
the estadiometer was placed in one of the walls of the research site and the 
 measurement used was the distance between the highest part of the head and the soles 
 of the feet , in upright position .
the volunteer was positioned so that the head was 
 aligned with the frankfurt plane ( imaginary line from the external auditory canal 
 until the lower orbit of the eye ) . to weigh the volunteers ,
the 
 volunteer was asked to look straight ahead while the weight was recorded by the 
 researcher .
brazilian economic classification 
 based on schooling level of the household head and the presence of household goods 
 and appliances in the house was used .
the families were categorized in eight economic 
 classes : a1 , a2 , b1 , b2 , c1 , c2 , d and e. the data from r24h were converted into energy and nutrients by the software dietwin 
 and the average consumption ( kcal ) was estimated .
moreover , they were separated in 11 
 food items : ice cream , fruits , chocolate , soft drink , greens , juices with added 
 sugar , biscuits ( with and without filling ) , vegetables , chocolate milk , sweets 
 ( chewing gum , candy ) to allow the comparison with the issues of the self - report 
 instrument .
the data about the ingested item , intake frequency and the time of the 
 food intake were checked in the r24h and the self - report measure .
we performed the data checking to ensure their reliability , examining 20 chips 
 randomly , and errors of data transcription were not found .
chi - square and student 's t test were used to compare the characteristics between the 
 sub - sample and the reference population .
the correspondence between the responses in the individual level was verified by 
 simple agreement and kappa statistics when the response categories showed balance , 
 and the difference between the highest and lowest value reached no more than 20% of 
 the respondents .
the responses on the intake frequency obtained through self - report 
 instrument were grouped into three categories : " one or more times a day " ; " up to 3 
 times over the past 15 days " ; " 4 to 6 times in the last 15 days " .
we could thus have 
 a better visualization of categories of frequency and could keep the category " one or 
 more times a day " apart .
the wilcoxon test was used to analyze the differences in average consumption 
 estimated by r24h and the self - report measure .
the chi - square of mcnemar test was 
 used to compare the differences in the percentage of respondents according to the 
 category " one or more times a day " and the intake moment ( only at mealtime or in 
 another moment ) .
assuming type 1 error equal to 5% and type 2 error equal to 20% , a 
 sample of 85 or more participants would be needed to detect an effect size 
 corresponding to 0.3 between the average daily intakes .
the same sample size would be 
 appropriated to detect a ratio between 1.8 and 2.2 between two proportions since the 
 relative frequency of discordant pairs ranged from 0.5 to 0.9 .
nutritionists trained under the supervision of the department of nutrition from the 
 public health school at the university of so paulo applied three 24 hours dietary 
 recalls ( r24h ) .
the dietary recalls were administered at nonconsecutive days to cover 
 a day in the weekend , setting up 15-day intervals between them .
the self - report instrument had 
 three questions for each one of the eleven food items .
the questions were about food 
 intake related to oral health , as well as frequency and the time of the day in which 
 the food was ingested .
the tools ( self - report measure and r24h ) were tested in a pilot study and adjusted 
 accordingly before being used in the feld .
the nutritionists used utensils such 
 as cups , plates , and spoons to apply r24h .
to examine the food behavior related to oral health in the past 15 days , the eleven 
 investigated items were ice cream , fruits , chocolate , soft drinks , vegetables , juices 
 with added sugar , biscuits ( with and without filling ) , greens , chocolate milk , and 
 sweets ( chewing gum , candy ) .
these items were selected based on the results of a 
 previous study on food intake conducted in piracicaba - sp , using data related to the intake average obtained 
 from two 24-hour recalls ( r24h ) applied in 93 adolescents .
the food items were chosen 
 taking into account the content of sucrose , the frequency of consumption and the 
 number of adolescents who reported the food intake .
data from food frequency were collected in six categories : 1 to 3 times in the last 
 15 days ; 4 to 6 times in the last 15 days ; 1 time a day ; 2 times a day ; 3 times a 
 day ; 4 or more times a day .
time of the day related to the food ingestion was 
 registered according to three categories : at mealtime ( breakfast , lunch or dinner ) , 
 at another moment ( mid - morning or mid - afternoon or evening before bedtime ) or both . 

items such as vegetables , greens and fruits were included based on questionnaires 
 from who ( 2010 ) and cdc about diet , due to the importance these foods in relation to 
 oral health - related behavior .
the measures of body weight and height of the adolescents were performed using a 
 digital scale with a capacity of 150 kg , sensitivity of 100 grams ( tanita , solar 
 digital scale hs 302 , tokyo , japan ) , and a portable estadiometer ( seca bodymeter 208 , 
 hamburg , germany ) .
the estadiometer was placed in one of the walls of the research site and the 
 measurement used was the distance between the highest part of the head and the soles 
 of the feet , in upright position .
the volunteer was positioned so that the head was 
 aligned with the frankfurt plane ( imaginary line from the external auditory canal 
 until the lower orbit of the eye ) . to weigh the volunteers ,
the 
 volunteer was asked to look straight ahead while the weight was recorded by the 
 researcher .
brazilian economic classification 
 based on schooling level of the household head and the presence of household goods 
 and appliances in the house was used .
the families were categorized in eight economic 
 classes : a1 , a2 , b1 , b2 , c1 , c2 , d and e.
the data from r24h were converted into energy and nutrients by the software dietwin 
 and the average consumption ( kcal ) was estimated .
moreover , they were separated in 11 
 food items : ice cream , fruits , chocolate , soft drink , greens , juices with added 
 sugar , biscuits ( with and without filling ) , vegetables , chocolate milk , sweets 
 ( chewing gum , candy ) to allow the comparison with the issues of the self - report 
 instrument .
the data about the ingested item , intake frequency and the time of the 
 food intake were checked in the r24h and the self - report measure .
we performed the data checking to ensure their reliability , examining 20 chips 
 randomly , and errors of data transcription were not found .
chi - square and student 's t test were used to compare the characteristics between the 
 sub - sample and the reference population .
the correspondence between the responses in the individual level was verified by 
 simple agreement and kappa statistics when the response categories showed balance , 
 and the difference between the highest and lowest value reached no more than 20% of 
 the respondents .
the responses on the intake frequency obtained through self - report 
 instrument were grouped into three categories : " one or more times a day " ; " up to 3 
 times over the past 15 days " ; " 4 to 6 times in the last 15 days " .
we could thus have 
 a better visualization of categories of frequency and could keep the category " one or 
 more times a day " apart .
the wilcoxon test was used to analyze the differences in average consumption 
 estimated by r24h and the self - report measure .
the chi - square of mcnemar test was 
 used to compare the differences in the percentage of respondents according to the 
 category " one or more times a day " and the intake moment ( only at mealtime or in 
 another moment ) .
assuming type 1 error equal to 5% and type 2 error equal to 20% , a 
 sample of 85 or more participants would be needed to detect an effect size 
 corresponding to 0.3 between the average daily intakes .
the same sample size would be 
 appropriated to detect a ratio between 1.8 and 2.2 between two proportions since the 
 relative frequency of discordant pairs ranged from 0.5 to 0.9 .
in this study , 87 of the 92 selected adolescents completed all phases of the research . 
 among these adolescents ,
39.2% were male and the mean age was 13.4 years old 
 ( sd=0.7 ) .
regarding socioeconomic level , 4.6% were class a2 , 24.1% were b1 , 43.7% were b2 , and 
 27.6% were c1 .
according to table 1 , there were 
 no statistically significant differences between the characteristics of the adolescents 
 included in the study and the participants of the representative sample from the city . 

the samples did not differ statistically by gender , body mass index ( bmi ) and 
 socioeconomic level .
characteristics of sample and subsample according to gender , body mass index 
 ( bmi ) , consumption of sweets , sugar and soft drinks .
piracicaba , brazil , 2011 notes : data sample ( 2007 ) and subsample ( 2011 ) sd = standard deviation the average energy intake in the 3 dietary recalls ( r24h ) in kcal was 2021.95 ( 671.64 ) , 
 and the maximum and minimum values were respectively 4612.71 and 633.72 .
the volunteers 
 had a mean weight of 54.67 kg , height of 1.60 m and bmi equal to 21.28 kg / m ; 
 21 were overweight and 7 were considered obese according to the who values .
the self - report instrument used was composed of 33 questions , 27 on the consumption of 
 sweet products ( containing sugar ) interspersed with 6 items related to consumption of 
 fruits , greens and vegetables .
the mean values obtained through the self - report instrument were always higher than 
 those reported by the r24h , with statistically significant differences for most items 
 ( wilcoxon p<0.05 ) , except ice cream , vegetables and biscuits without filling ( table 2 ) .
there were no differences between boys 
 and girls when the analysis was stratified by gender ( data not shown ) .
mean , median , and standard deviation ( sd ) of daily intake ( grams ) assessed by 
 three r24hs and a self - report measure ( srm ) , in 87 adolescents attending public 
 schools in piracicaba , brazil , 2011 wilcoxon test ( p<0.05 ) the higher spearman 's correlations were found for the items ice cream ( rs=0.35 , p=0.00 ) , 
 soft drink ( rs=0.39 , p=0.00 ) and chocolate milk ( rs=0 , 38 , p=0.00 ) , positioning them on 
 the edge between a weak and moderate correlation . for fruits ( rs=0.23 , p=0.03 ) , biscuits 
 without filling ( rs=0.15 , p=0.15 ) , and sweets / candy / gum ( rs=0.25 , p=0.02 ) , the observed 
 values showed a weak correlation . for other items ,
the percentage of adolescents who reported intake frequency " one or more times daily " 
 was higher than the value obtained through r24h for all food items , except soft drinks 
 ( table 3 ) . regarding the time of intake ( only 
 at the mealtime or at another time ) , there was no statistically significant difference 
 for the items greens , juice with added sugar , vegetables , chocolate milk , biscuits 
 without filling and sweets ( chewing gum , candy ) . for four of the five remaining items , 
 namely ice cream , fruits , chocolate , soft drink and biscuits with filling , significant 
 differences were observed leading to an overestimation of the intake in other times 
 ( table 3 ) .
percentage of adolescents according to their intake frequency over the past 15 
 days and time of the day of intake , both assessed by r24hs and self - report measure 
 ( srm ) .
piracicaba , brazil , 2011 statistical test not applied at the individual level , the kappa statistic was applied only for soft drinks ( 0.27 ) and 
 sweets/ candy / gum ( 0.15 ) , with level of agreement rated as " considerable " and " mild " 
 consecutively .
higher values of crude agreement between instruments , individually , were for the items 
 biscuits without filling ( 75.9% ) , ice cream ( 72.4% ) , chocolate ( 57.5% ) and soft drinks 
 ( 56.3% ) ( figure 1 ) .
percentage of agreement ( % ) related to the responses obtained through the r24h and 
 by the self - report measure ( srm ) according to the intake frequency and type of 
 food , piracicaba , 2011 , brazil in relation to the time of sugary food intake , the r24h showed that soft drinks and 
 sweets are consumed in other times besides the main meals , reaching 77.0% of agreement 
 between the instruments ( figure 2 ) .
percentage of responses of crude agreement ( % ) and kappa test comparing the r24h 
 and the self - report measure ( srm ) , according to the time of the day and type of 
 food ingested , piracicaba , 2011 , brazil the kappa test was only possible to apply for the soft drink and the value was 
 considered " mild " ( 0.10 ) .
sugars have an evidenced etiologic role in to tooth decay , not only by the amount of the 
 sugar ingested , but mainly by the frequency of intake .
thus , the instruments aiming to measure this consumption 
 are important to deepen understanding of the relationship between food behavior and 
 dental caries in a context of multiple sources of fluoride .
therefore , comparing estimates of dietary behavior related to oral health among 
 adolescents produced by a self - report instrument and by 24 hour recalls is important to 
 verify the reliability of these instruments . in the present study ,
we assessed the degree 
 of crude agreement of responses , the average intake estimates , and the percentage 
 distribution of participants according to the frequency of food intake in the last 15 
 days and the time of consumption .
the measurement of the degree of agreement between the values produced by both tools was 
 made in relation to the categories of consumption frequency and time of intake ( only at 
 mealtime and at another moment ) .
values of crude agreement equal or higher than 70% regarding the time of ingestion were 
 observed for four food items . in relation to the intake frequency , this agreement level 
 was noticed only for two items , which may indicate that adolescents have more readiness 
 to describe the moment of food intake than its frequency in the last 15 days .
the degree of correlation between the average daily intakes was estimated as weak for 
 the most studied foods .
only items as ice cream ( rs=0.35 , p=0.00 ) , soft drink ( rs=0.39 , 
 p=0.00 ) and chocolate milk ( rs=0.38 , p=0.00 ) presented weak to moderate correlation 
 suggesting that the deviations are not homogeneous or subject to a linear 
 correction .
the proportion of adolescents who reported intake frequency " one or more times daily " 
 for a particular food was higher than the estimate obtained by reference measure for all 
 items , except for the soft drink , which displayed equivalent consumption .
the 
 implication is that the estimates provided by the self - report measure should be used 
 with caution .
according to the reference method , the percentage of adolescents who reported intake 
 frequency " one or more times a day " for fruits , greens and vegetables was always lower 
 than the value estimated by self - report measure .
the results suggest that adolescents , before a self - report instrument , tend to report a 
 degree of exposure to the food items larger than actually experience in their daily 
 lives . regarding the moment of ingestion , no tendency for overestimating
for some items whose estimates differed , it was observed that 
 the most frequent category changed from mealtime to other times outside the main meal . 

this occurred for the items ice cream , fruits , chocolate , soft drink , and biscuits with 
 filling , which may suggest that in the face to face interview , a feature of reference 
 method , adolescents tend to underestimate the consumption of these products outside the 
 period of the mealtime . in this case
, the self - report measure might be a useful tool 
 considering that different behaviors in relation to the expected standard are less 
 reported in a face to face interview .
deviations in the estimation of food behavior are highlighted by several researchers . 
 some of them have argued that teenagers tend to remember only the preferred foods and do 
 not possess the time dimension completely formed .
there is a reasonable increase from individuals 7 - 8 years to 12 years of age in the 
 ability of children to participate in dietary recalls , but only for the food consumed in 
 the immediate past , corresponding to the last 24 hours .
parental involvement may be important to provide details about the types and amounts of 
 food consumed , as children have not completed their cognitive development .
however , the 
 help of the parents is not a solution to all difficulties of assessing the diet of the 
 children , particularly if the study is concerned about evaluating what is consumed 
 between main meals , in the period when the kids are at school or in other places out of 
 their parents ' sight . in the case of adolescents , additional difficulties associated with patterns of 
 irregular diet , including eating out of the house , and concern with self - image can 
 contribute to a greater or lesser lack of accuracy in reporting habitual diet .
in recent years , changes have been 
 observed in the social context of eating with a shift from a pattern based on family 
 meal to a pattern based on more irregular and solitary eating .
this not only increases 
 the frequency of consumption but also confuses the function of the foods .
items that 
 traditionally were part of the main meal and did not pose a risk to the oral health have 
 become a threat , as the introduction of the snacks in other moments during the 
 day .
some authors have emphasized that adolescents do not have cognitive maturity for 
 decision - making .
they would be influenced by emotional factors , because some factors of 
 configural stimuli are still being formed in the adolescence .
thus , to ask 
 for a teen to answer an instrument that assesses food consumption in the last 15 days 
 may require a mental and cognitive effort beyond his / her ability , leading to errors in 
 the estimation of food consumption .
it is important to point out that the discrepancies in this study were found in a sample 
 size relatively too small to detect differences between the estimates produced by 
 different measurement instruments .
the characteristics of volunteers who formed the 
 present investigation did not differ from the representative sample of adolescents who 
 participated in the previous study in the same county .
in addition to demographic 
 characteristics , the composition according to body mass and exposure to sugary products , 
 both by frequency and by the amount ingested , were equivalent .
while this represents a 
 strong aspect of the study , a limitation is that it was not possible to ensure a more 
 balanced frequency for some food items , which would have allowed the application of 
 kappa test .
food items that composed the instrument were selected based on a previous 
 study , which was conducted with participants of similar age enrolled in the same 
 city .
nevertheless , for two items investigated by the reference 
 method , none was consumed by adolescents at least once a day . in spite of indicators related to group analysis have showed better application when 
 compared to individual analysis indicators since the kappa test could not be applied to 
 all food groups , from a clinical point of view , the results suggest that the utilization 
 of self - report instrument can lead to an overestimation of individual exposure compared 
 to r24h . to minimize recall bias , one might make use of food weighing as the " gold standard " . 

the present study used kitchen 
 utensils , glasses and cups to help the adolescents remember the consumed amount in the 
 previous day , making sure to apply the 24-hour recall at least one day after the 
 weekend , since the diet might vary in this period .
the method was applied by trained nutritionists . 
 to apply the self - report instrument ,
the adolescents were divided in small groups , 
 distant from each other in individual portfolio , always with the presence of the 
 researcher responsible to aid in case of any doubt .
there was considerable variability in the degree of concordance between the instruments , 
 at the individual level , depending on the type of food .
the response of the adolescents 
 led to an overestimating of daily intake for 8 out of 11 food items measured by the 
 self - report instrument .
the percentage of adolescents that reported the intake frequency 
 " one or more time daily " was higher than the estimate obtained through r24h for all food 
 items , excepting soft drinks .
further studies are needed to develop a self - report measure 
 particularly for items in which there was an overestimation .
 objectiveto compare estimates of food behavior related to oral health obtained through a 
 self - report measure and 24 hour dietary recalls ( r24h).methodwe applied three r24h and one self - report measure in 87 adolescents . 
 the estimates 
 for eleven food items were compared at individual and group levels.resultsno significant differences in mean values were found for ice cream , vegetables and 
 biscuits without filling . for the remaining items , the values reported by the 
 adolescents were higher than the values estimated by r24h . 
 the percentage of 
 adolescents who reported intake frequency of 1 or more times/ day was higher than 
 the value obtained through r24h for all food items except soft drinks . 
 the highest 
 values of crude agreement between the instruments , individually , were found in the 
 biscuits without filling ( 75.9% ) and ice cream ( 72.4%).conclusionthe results suggest that adolescents tend to report a degree of exposure to the 
 food items larger than what they actually experience in their daily lives . 
INTRODUCTION
MATERIAL AND METHODS
Measurement of food behavior
Instruments
Food items
Weight and height
Socioeconomic data
Data analysis
RESULTS
DISCUSSION
CONCLUSION