the study was approved by the ethics commission of vaud canton ( protocol number 172/08 ) and was conducted between september and december 2008 . inclusion criteria were : ages between 25 and 65 years , no illness or disease requiring a specific diet ( e.g. diabetes , food allergies , renal insufficiency ) , not on a weight reduction diet , an adequate knowledge of french , and a good memory to perform a valid dietary recall . although diabetics are recommended to follow  the same diet as healthy persons , we decided to exclude them on the fact that the swiss diabetes association indicated that  type 1 diabetes needs ,  a specific diet and that  the first measure to take in case of type 2 diabetes is to change one 's lifestyle , by dieting ( eating healthier) ( http://www.diabetesgesellschaft.ch/fr/informations/sur-diabete/ , assessed march 30 , 2011 ) , thus suggesting that diabetic subjects should have diets distinct from healthy persons . the food frequency questionnaire was based on previously developed ffqs ( 6 , 15 ) , as well as elements from other ffq designs ( 1 ) . this ffq consists of questions about 126 items : 105 on foods or specific dishes ( e.g. fondue , vegetable soup , pizza ) , five on nutritional supplements , and 16 on beverages ( alcoholic and non - alcoholic ) . the 126 food items were selected from existing swiss ffq ( primarily bus sant , dating from 1990 ( 15 ) , and an ffq developed by wynn - dumartheray et al . major ffqs used in the united states to ensure completeness in terms of food groups . twenty - four hours recall data confirmed that the ffq covered the main foods consumed in the region . foods were classified into 10 groups : dairy products , bread , and cereals ; spreads ; meat and protein - rich foods ( including eggs and tofu ) ; fish and seafood ; vegetables ; starchy foods ( including potatoes and rice ) ; fruits ( including berries , canned , dried or in syrup ) ; pastries , sweets and snacks ; spices and sauces . for each item , subjects were asked to indicate their intake over the past month , and there were eight frequencies of consumption ranging from  never / less than once per month to  5 + per day. in switzerland , sales of fruit drink ( normally < 25% fruit juice ) are high , and there is considerable confusion between fruit juice and fruit drink . as there was a risk in greatly overestimating fruit intake if  fruit juice was included as fruit ( due to the potentially high volumes consumed ) , juice was included as a beverage . supplements were selected as the most common supplements taken  including vitamins c and e , generic multivitamins , and fish oil . the ffqs were filled manually and the data was also handled ( keyed in ) manually , as our previous experience in another study with optical reading showed an unacceptably high rate of errors . the interviews were chronologically based ; that is , from the first to the last meal of the previous day . food portion sizes were estimated using standard household measures such as cups and spoons and a french food and beverage photo manual ( 16 ) . while the ffq gave precise and fixed portions ( the same for everyone ) , during the 24-hour recall , the exact portion was defined with each subject . participants were asked to be as specific as possible about the type of food and beverage consumed ( e.g. skimmed or non - skimmed milk ) , including type of cooking method used ( e.g. roasted , boiled , etc . ) . when subjects reported eating a personal recipe , the dietician asked the subject complete information on each individual food item ( quality and quantity ) . for example , if the subject reported eating homemade lasagna , then all the different items were calculated separately ( pasta , tomato sauce , onions , hard cheese , minced beef , and olive oil ) . weight and height in light clothes were measured and the participants were also asked about current tobacco smoking . twenty - four hour dietary recalls were performed the day after the participants had filled the ffq , a protocol also used by others ( 17 ) . energy and macronutrient intake from the 24-hour dietary recalls was estimated using the prodi food composition database ( nutri - science gmbh , hausach , germany ) , which also includes information from the swiss national nutrient database ( http://www.swissfir.ethz.ch/index_en ) . energy and macronutrient intake from the ffq was estimated using a composite nutrient database based on the swiss nutrient database and supplemented with data from the french , german , and uk databases when data was not available or appropriate . notably , cooked meat products are not yet included in the swiss database , so these values were taken from the databases of neighboring countries . where a food item included several different foods or types of preparation , all foods were included and an average was taken . statistical analysis was conducted using stata version 9.2 ( statacorp , college station , tx , usa ) . descriptive results were expressed as number and ( percentage ) or as meanstandard deviation for nutrient intake . reproducibility between the first and the second ffq was assessed by intraclass correlation coefficients ( icc ) , where a higher value indicates a lower within - person variation . the natural logarithm of nutrient intake was used to achieve normal distributions ( 17 ) . validity of the ffq was assessed as follows : pearson 's correlation between the ffq and the 24-hour recall estimations of nutrient intake were calculated . between ( sb2 ) and within ( sw2)-person daily variances for each nutrient were computed . the corresponding de - attenuated pearson 's coefficients were then calculated by multiplying the initial pearson 's coefficient by 1+{(sw2/sb2)/2 } , as the 24-hour recall was repeated twice . it measures how well a new set of observations reproduces an original set and has been reported to be more appropriate than other indices for measuring agreement when the variable of interest is continuous ( 18 ) . it has also been shown to be robust on as few as 10 pairs of data . participants were also classified into tertiles of energy and nutrient intake , based on the ffq and the average of the 24-hour recalls . proportions of participants classified into the same , adjacent , and extreme tertiles by ffq and 24-hour recalls were then calculated for energy and each nutrient . the study was approved by the ethics commission of vaud canton ( protocol number 172/08 ) and was conducted between september and december 2008 . inclusion criteria were : ages between 25 and 65 years , no illness or disease requiring a specific diet ( e.g. diabetes , food allergies , renal insufficiency ) , not on a weight reduction diet , an adequate knowledge of french , and a good memory to perform a valid dietary recall . although diabetics are recommended to follow  the same diet as healthy persons , we decided to exclude them on the fact that the swiss diabetes association indicated that  type 1 diabetes needs ,  a specific diet and that  the first measure to take in case of type 2 diabetes is to change one 's lifestyle , by dieting ( eating healthier) ( http://www.diabetesgesellschaft.ch/fr/informations/sur-diabete/ , assessed march 30 , 2011 ) , thus suggesting that diabetic subjects should have diets distinct from healthy persons . the food frequency questionnaire was based on previously developed ffqs ( 6 , 15 ) , as well as elements from other ffq designs ( 1 ) . this ffq consists of questions about 126 items : 105 on foods or specific dishes ( e.g. fondue , vegetable soup , pizza ) , five on nutritional supplements , and 16 on beverages ( alcoholic and non - alcoholic ) . the 126 food items were selected from existing swiss ffq ( primarily bus sant , dating from 1990 ( 15 ) , and an ffq developed by wynn - dumartheray et al . major ffqs used in the united states to ensure completeness in terms of food groups . twenty - four hours recall data confirmed that the ffq covered the main foods consumed in the region . foods were classified into 10 groups : dairy products , bread , and cereals ; spreads ; meat and protein - rich foods ( including eggs and tofu ) ; fish and seafood ; vegetables ; starchy foods ( including potatoes and rice ) ; fruits ( including berries , canned , dried or in syrup ) ; pastries , sweets and snacks ; spices and sauces . for each item , subjects were asked to indicate their intake over the past month , and there were eight frequencies of consumption ranging from  never / less than once per month to  5 + per day. in switzerland , sales of fruit drink ( normally < 25% fruit juice ) are high , and there is considerable confusion between fruit juice and fruit drink . as there was a risk in greatly overestimating fruit intake if  fruit juice was included as fruit ( due to the potentially high volumes consumed ) , juice was included as a beverage . supplements were selected as the most common supplements taken  including vitamins c and e , generic multivitamins , and fish oil . the ffqs were filled manually and the data was also handled ( keyed in ) manually , as our previous experience in another study with optical reading showed an unacceptably high rate of errors . the interviews were chronologically based ; that is , from the first to the last meal of the previous day . food portion sizes were estimated using standard household measures such as cups and spoons and a french food and beverage photo manual ( 16 ) . while the ffq gave precise and fixed portions ( the same for everyone ) , during the 24-hour recall , the exact portion was defined with each subject . participants were asked to be as specific as possible about the type of food and beverage consumed ( e.g. skimmed or non - skimmed milk ) , including type of cooking method used ( e.g. roasted , boiled , etc . ) . when subjects reported eating a personal recipe , the dietician asked the subject complete information on each individual food item ( quality and quantity ) . for example , if the subject reported eating homemade lasagna , then all the different items were calculated separately ( pasta , tomato sauce , onions , hard cheese , minced beef , and olive oil ) . weight and height in light clothes were measured and the participants were also asked about current tobacco smoking . twenty - four hour dietary recalls were performed the day after the participants had filled the ffq , a protocol also used by others ( 17 ) . energy and macronutrient intake from the 24-hour dietary recalls was estimated using the prodi food composition database ( nutri - science gmbh , hausach , germany ) , which also includes information from the swiss national nutrient database ( http://www.swissfir.ethz.ch/index_en ) . energy and macronutrient intake from the ffq was estimated using a composite nutrient database based on the swiss nutrient database and supplemented with data from the french , german , and uk databases when data was not available or appropriate . notably , cooked meat products are not yet included in the swiss database , so these values were taken from the databases of neighboring countries . where a food item included several different foods or types of preparation , all foods were included and an average was taken . statistical analysis was conducted using stata version 9.2 ( statacorp , college station , tx , usa ) . descriptive results were expressed as number and ( percentage ) or as meanstandard deviation for nutrient intake . reproducibility between the first and the second ffq was assessed by intraclass correlation coefficients ( icc ) , where a higher value indicates a lower within - person variation . the natural logarithm of nutrient intake was used to achieve normal distributions ( 17 ) . validity of the ffq was assessed as follows : pearson 's correlation between the ffq and the 24-hour recall estimations of nutrient intake were calculated . between ( sb2 ) and within ( sw2)-person daily variances for each nutrient were computed . the corresponding de - attenuated pearson 's coefficients were then calculated by multiplying the initial pearson 's coefficient by 1+{(sw2/sb2)/2 } , as the 24-hour recall was repeated twice . it measures how well a new set of observations reproduces an original set and has been reported to be more appropriate than other indices for measuring agreement when the variable of interest is continuous ( 18 ) . it has also been shown to be robust on as few as 10 pairs of data . participants were also classified into tertiles of energy and nutrient intake , based on the ffq and the average of the 24-hour recalls . proportions of participants classified into the same , adjacent , and extreme tertiles by ffq and 24-hour recalls were then calculated for energy and each nutrient . forty adults ( 23 men , 17 women , mean age 43.12.0 year , mean bmi 24.13.6 kg / m ) participated in the study . participants took on average 2210 ( range : 1060 ) min to fill out the ffq , and this value decreased between the first and the second evaluation : 2511 versus 208 min , respectively ( p<0.001 ) . over 90% of participants considered the questions as easy ( 93% in the first and 95% in the second evaluations , p=0.64 ) . the mean macronutrient intakes of the 24-hour dietary recalls , first , and second ffq are presented in table 1 ) . the absolute values estimated by the second ffq were significantly lower than those estimated by the first ffq for energy , protein , and carbohydrates , while no differences were found for the other nutrients . excluding a subject with a very high protein intake did not change the results ( data not shown ) . crude pearson 's correlation coefficients between the first and the second ffq ranged from 0.58 for water to 0.90 for alcohol . the iccs ranged between 0.53 for water and 0.92 for alcohol , and lin 's concordance ranged from 0.55 for water and 0.87 for alcohol . when participants were classified into tertiles of macronutrient intake , the proportion of classification into the same tertile ranged from 40% for carbohydrates to 77.5% for alcohol . on average , over 95% of the participants fell into the same or the adjacent categories ( table 2 ) . non - parametric correlation coefficients using non - transformed data showed that the values ranged between 0.57 for water and 0.85 for polyunsaturated fatty acids and alcohol . mean daily intakes of energy and macronutrients estimated from two 24-hour recalls and the ffqs correlation coefficients computed using log - transformed data . ffq , food - frequency questionnaire ; r , pearson correlation coefficient ; c , lin 's concordance correlation coefficient ; icc , intraclass correlation coefficient . statistical analysis by student 's paired t - test on log - transformed values between each ffq and the 24-hour report : statistical analysis by student 's paired t - test on log - transformed values between each ffq : reproducibility of the food frequency questionnaires results are expressed as percentage of participants classified in the same , adjacent , or extreme tertiles of nutrient distribution by the first and the second ffq ( n=40 ) . macronutrient intakes estimated by both ffq were significantly higher than those estimated from the 24-hour recalls for protein and water , while no significant differences were found for energy and the other macronutrients ( tables 1 and 3 ) . crude pearson 's correlation coefficients between the 24-hour recall and the second ffq tended to be higher than with the first ffq ( table 3 ) . the crude pearson 's correlation coefficients ranged between 0.23 and 0.44 for the first ffq and between 0.32 and 0.57 for the second ffq . de - attenuated correlation coefficients were higher , but the improvement was modest as the variance ratios were small ( table 3 ) . lin 's concordance correlation coefficients were also higher between the second ffq and the 24-hour recall than between the first ffq and the 24-hour recall ( table 3 ) ; for ffq2 , the values ranged between 0.31 for cholesterol and 0.54 for water . the classification into tertiles gave similar results for both ffq : for ffq1 , an average of 43 and 85% of participants classified in the same or adjacent tertile , respectively , the corresponding figures for ffq2 being 46 and 88% ( table 4 ) . validity of the ffqs versus the average of two 24-hour recalls correlation coefficients computed using log - transformed data . r , pearson correlation coefficient ; c , lin 's concordance correlation coefficient ; rde - att , ffq and 24-hour de - attenuated pearson 's correlation coefficient . ratio between within - person ( sb2 ) and between - person ( sw2 ) daily variances computed with the two 24-hour recall . validity of the ffqs versus the average of two 24-hour recalls results are expressed as percentage of subjects within the same , adjacent , or extreme tertiles . forty adults ( 23 men , 17 women , mean age 43.12.0 year , mean bmi 24.13.6 kg / m ) participated in the study . participants took on average 2210 ( range : 1060 ) min to fill out the ffq , and this value decreased between the first and the second evaluation : 2511 versus 208 min , respectively ( p<0.001 ) . over 90% of participants considered the questions as easy ( 93% in the first and 95% in the second evaluations , p=0.64 ) . the mean macronutrient intakes of the 24-hour dietary recalls , first , and second ffq are presented in table 1 ) . the absolute values estimated by the second ffq were significantly lower than those estimated by the first ffq for energy , protein , and carbohydrates , while no differences were found for the other nutrients . excluding a subject with a very high protein intake did not change the results ( data not shown ) . crude pearson 's correlation coefficients between the first and the second ffq ranged from 0.58 for water to 0.90 for alcohol . the iccs ranged between 0.53 for water and 0.92 for alcohol , and lin 's concordance ranged from 0.55 for water and 0.87 for alcohol . when participants were classified into tertiles of macronutrient intake , the proportion of classification into the same tertile ranged from 40% for carbohydrates to 77.5% for alcohol . on average , over 95% of the participants fell into the same or the adjacent categories ( table 2 ) . non - parametric correlation coefficients using non - transformed data showed that the values ranged between 0.57 for water and 0.85 for polyunsaturated fatty acids and alcohol . mean daily intakes of energy and macronutrients estimated from two 24-hour recalls and the ffqs correlation coefficients computed using log - transformed data . ffq , food - frequency questionnaire ; r , pearson correlation coefficient ; c , lin 's concordance correlation coefficient ; icc , intraclass correlation coefficient . statistical analysis by student 's paired t - test on log - transformed values between each ffq and the 24-hour report : statistical analysis by student 's paired t - test on log - transformed values between each ffq : reproducibility of the food frequency questionnaires results are expressed as percentage of participants classified in the same , adjacent , or extreme tertiles of nutrient distribution by the first and the second ffq ( n=40 ) . macronutrient intakes estimated by both ffq were significantly higher than those estimated from the 24-hour recalls for protein and water , while no significant differences were found for energy and the other macronutrients ( tables 1 and 3 ) . crude pearson 's correlation coefficients between the 24-hour recall and the second ffq tended to be higher than with the first ffq ( table 3 ) . the crude pearson 's correlation coefficients ranged between 0.23 and 0.44 for the first ffq and between 0.32 and 0.57 for the second ffq . de - attenuated correlation coefficients were higher , but the improvement was modest as the variance ratios were small ( table 3 ) . lin 's concordance correlation coefficients were also higher between the second ffq and the 24-hour recall than between the first ffq and the 24-hour recall ( table 3 ) ; for ffq2 , the values ranged between 0.31 for cholesterol and 0.54 for water . the classification into tertiles gave similar results for both ffq : for ffq1 , an average of 43 and 85% of participants classified in the same or adjacent tertile , respectively , the corresponding figures for ffq2 being 46 and 88% ( table 4 ) . validity of the ffqs versus the average of two 24-hour recalls correlation coefficients computed using log - transformed data . r , pearson correlation coefficient ; c , lin 's concordance correlation coefficient ; rde - att , ffq and 24-hour de - attenuated pearson 's correlation coefficient . ratio between within - person ( sb2 ) and between - person ( sw2 ) daily variances computed with the two 24-hour recall . validity of the ffqs versus the average of two 24-hour recalls results are expressed as percentage of subjects within the same , adjacent , or extreme tertiles . in this study , we assessed the reproducibility and relative validity for energy and macronutrient intake of a ffq designed for french - speaking swiss adults . the objective was to obtain an ffq that could be easily and quickly filled out by a majority of adults . the length of the ffq ( 126 items ) is similar to other ffqs used for epidemiological studies ( 6 , 17 , 19 ) . the average time for filling out the ffq was less than half an hour , so we believe that this ffq can be easily applied in an epidemiological setting . the reproducibility of ffq was good considering the observed correlation coefficients and icc being either higher than ( 17 , 19 ) or within values reported from the literature ( 20 ) ( table 5 ) for ffq validated with multiple 24-hour recall . comparison of the reproducibility ( r and icc ) between this study and the literature study 2 : first value men , second value women ; na , not available . balancing the reference method with the period covered by the ffq is a critical factor in the study design , with a need to not have the repeated 24-hour recalls too close together to avoid subjects remembering their previous answers , but not too far apart , to avoid seasonal changes in diet and to keep within the period defined by the ffq . the time intervals used by other authors vary considerably , from 15 days ( 21 ) to 1 year ( 17 , 20 , 2224 ) . food intake also shows yearly trends ( 2527 ) , and we believe that the 1-month period between the two questionnaires is an adequate time interval , to avoid undue influence of seasonal and/or yearly variations . in agreement with some studies ( 17 ) , it was decided to apply the 24-hour recall the day after the ffq . this methodology precludes the ffq to cover the period of the 24-hour recall , thus reducing validity ; hence , it is likely that our validity measures could have been better had the 24-hour recall be conducted before the application of the ffq . finally , the close timing between the ffq and the 24-hour recall might lead to interference , unless there is a very long time between measurements  in which case the same period is not being measured . a higher agreement between the second ffq and the 24-hour recall has been reported in several studies ( 2 , 17 , 22 ) . this could be due to the fact that filling out the first ffq actually made the participants more conscious of their dietary intake , thus leading to a better reporting of their dietary intake . in this study , the agreement between the first and the second ffq with the 24-hour recall were rather close , probably because the rather short time between the two assessments did not allow the participants to change significantly their dietary intake . overall , the agreement was slightly lower than reported in other studies ( 28 , 29 ) , but comparable to others ( 17 , 19 , 30 ) . furthermore , around 80% of the participants were classified in the same or adjacent tertile according to their energy or macronutrient intake , the values being slightly higher for the second ffq . the relatively small number of participants and number of reference replicates used in this study are possible limitations . it has been suggested that the minimum sample size for validation studies is 100 , namely when the number of replicates of the reference method is small ( 31 ) . power analyses indicated that the minimum sample size need to obtain a significant correlation of 0.4 between the ffq and the 24-hour recall was 30 ( 17 , 19 , 32 ) , a value below our sample size of 40 . in terms of the number of repeated 24-hour recall measurements needed , several studies have shown that an adequate statistical efficiency is obtained with only two replicate measures to remove the effects of within - person variation ( 33 , 34 ) . hence , we believe that the two 24-hour replicates were enough to adequately assess the attenuation coefficient in this study . while overall correlations between the ffq and 24-hour recalls were acceptable , a probable reason for some of the difference observed is that different nutrient databases were used to calculate the nutrient intakes for the ffq and 24-hour recall . in constructing the composite nutrient database for the ffq , when a food item was not adequately covered by the swiss nutrient database , appropriate foods were substituted from other nutrient databases , and cross - checked to ensure that they were within a probable range for that nutrient . for example , protein in meat differed between the composite database designed for this ffq and the swiss nutrient database used for the 24-hour recall , due to cooked meat values being used for the ffq , but raw meat being used for the 24-hour recall ( data not shown ) . in addition , for some nutrients , missing values were evident in the swiss database , which were completed in the composite database . due to the software involved , it was not possible to use the composite nutrient database for the 24-hour recall calculations . further , it was not possible to have had an exhaustive list of all vitamin supplements available in switzerland , so a precise estimation of micronutrient intake could not be performed . although only one participant ( 2.5% ) reported taking vitamin supplements , previous data suggests that the prevalence of nutritional supplement use in switzerland is considerably higher ( 35 ) . hence , further efforts are needed to better assess vitamin and mineral intake in the swiss population , as this could not be achieved with the current ffq . the ffq was initially designed for specific studies taking place within the french - speaking region . however , the food available in switzerland is more or less homogenous ( from supermarket data ) , though there are differences in the proportions of different foods eaten . it is thus possible that this ffq could be applied to the german- and italian - speaking swiss populations given the generic availability of most foods included in the ffq , even if there would be generally greater consumption in one part of the country compared to others . this ffq is a valid instrument for determining macronutrient intake in a french - speaking swiss population in an epidemiological setting , with comparable results to other ffq validation studies . alastair ross , emma wynn , serge rezzi , and bernard decarli are full - time employees of nestl , a food company .
backgrounddue to the distinct cultural and language differences that exist in switzerland , there is little information on the dietary intake among the general swiss population . 
 adequately assessing dietary intake is thus paramount if nutritional epidemiological studies are to be conducted.objectiveto assess the reproducibility and validity of a food - frequency questionnaire ( ffq ) developed for french - speaking swiss adults.designa total of 23 men and 17 women ( 43.12.0 years ) filled out one ffq and completed one 24-hour dietary recall at baseline and 1 month afterward.resultscrude pearson 's correlation coefficients between the first and the second ffq ranged from 0.58 to 0.90 , intraclass correlation coefficient ( icc ) ranged between 0.53 and 0.92 . 
 lin 's concordance coefficients ranged between 0.55 and 0.87 . 
 over 80% of participants were classified in the same or adjacent tertile using each ffq . 
 macronutrient intakes estimated by both ffqs were significantly higher than those estimated from the 24-hour recall for protein and water , while no significant differences were found for energy , carbohydrate , fats ( five groups ) , and alcohol . 
 de - attenuated pearson 's correlation coefficients between the 24-hour recall and the first ffq ranged between 0.31 and 0.49 , while for the second ffq the values ranged between 0.38 and 0.59 . over 40 and 95% of participants fell into the same or the adjacent energy and nutrient tertiles , respectively , using the ffqs and the 24-hour recall.conclusionsthis ffq shows good reproducibility and can be used determining macronutrient intake in a french - speaking swiss population in an epidemiological setting .