Validation of the Danish 7-day pre-coded food diary among adults: energy intake v. energy expenditure and recording length

Under-reporting of energy intake (EI) is a well-known problem when measuring dietary intake in free-living populations. The present study aimed at quantifying misreporting by comparing EI estimated from the Danish pre-coded food diary against energy expenditure (EE) measured with a validated position-and-motion instrument (ActiReg (R)). Further, the influence of recording length on El:BMR, percentage consumers, the number of meal occasions and recorded food items per meal was examined. A total of 138 Danish volunteers aged 20-59 years wore the ActiReg (R) and recorded their food intake for 7 consecutive days. Data for 2504 participants from the National Dietary Survey 2000-2 were used for comparison of characteristics and recording length. The results showed that EI was underestimated by 12% on average compared with EE measured by ActiReg (R) (PreMed AS, Oslo, Norway). The 95% limits of agreement for EI and EE were -6.29 and 3.09 MJ/d. Of the participants, 73% were classified as acceptable reporters, 26% as under-reporters and 1% as over-reporters. EI:BMR was significantly lower on 1-3 consecutive recording days compared with 4-7 recording days (P<0.03). Percentage consumers of selected food items increased with number of recording days. When recording length was 7d, the number of reported food items per meal differed between acceptable reporters and under-reporters. EI:BMR was the same on 4 and 7 consecutive recording days. This was, however, a result of under-reporting in the beginning and the end of the 7d reporting. Together, the results indicate that EI was underestimated at group level and that a 7d recording is preferable to a 4d recording period.