title: Validation of web-based, multiple 24-h recalls combined with nutritional supplement intake questionnaires against nitrogen excretions to determine protein intake in Dutch elite athletes.
abstract: Information on dietary composition is vitally important for elite athletes to optimise their performance and recovery, which requires valid tools. The aim of the present study was to investigate the validity of assessing protein intake using three web-based 24-h recalls and questionnaires, by comparing these with three urinary N excretions on the same day. A total of forty-seven Dutch elite top athletes, both disabled and non-disabled, aged between 18 and 35 years, with a BMI of 17·5-31 kg/m2, exercising >12 h/week were recruited. Estimated mean dietary protein intake was 109·6 (sd 33·0) g/d by recalls and questionnaires v. 141·3 (sd 38·2) g/d based on N excretions in urine; the difference was 25·5 (sd 21·3) % between the methods (P<0·05). We found a reasonably good association between methods for protein intake of 0·65 (95 % CI 0·45, 0·79). On an individual level, under-reporting was larger with higher protein intakes than with lower intakes. No significant differences were found in reporting absolute differences between subcategories (sex, under-reporting, BMI, collection of recalls within a certain amount of time and using protein supplements or not). In conclusion, combined, multiple, 24-h recalls and questionnaires underestimated protein intake in these young elite athletes more than that reported for non-athlete populations. The method proved to be suitable for ranking athletes according to their protein intake as needed in epidemiological studies. On an individual level, the magnitude of underestimation was about equal for all athletes except for those with very high protein intakes.
authors.affiliation: 1Sports and Exercise Studies,HAN University of Applied Sciences,6525 AJ Nijmegen,The Netherlands.
authors.forename: F C
authors.initials: FC
authors.lastname: Wardenaar
authors.affiliation: 1Sports and Exercise Studies,HAN University of Applied Sciences,6525 AJ Nijmegen,The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Steennis
authors.affiliation: 1Sports and Exercise Studies,HAN University of Applied Sciences,6525 AJ Nijmegen,The Netherlands.
authors.forename: I J M
authors.initials: IJ
authors.lastname: Ceelen
authors.affiliation: 2Division of Human Nutrition,Wageningen University,6708 PB Wageningen,The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Mensink
authors.affiliation: 2Division of Human Nutrition,Wageningen University,6708 PB Wageningen,The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Witkamp
authors.affiliation: 2Division of Human Nutrition,Wageningen University,6708 PB Wageningen,The Netherlands.
authors.forename: J H M
authors.initials: JH
authors.lastname: de Vries
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D004044:Dietary Proteins / Q000008:administration & dosage*; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D020407:Internet; D008297:Male; D009584:Nitrogen / Q000652:urine*; D013177:Sports; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen
keywords: 24-h recalls; Athletes; EI energy intake; FIL food intake level; Nitrogen excretion; PABA 
                    para-aminobenzoic acid; PAL physical activity level; Validation