Daily, weekly, seasonal, within- and between-individual variation in nutrient intake according to four season consecutive 7 day weighed diet records in Japanese female dietitians.
OBJECTIVE
To study daily, weekly, seasonal, within- and between-individual variance in intake of selected nutrients and minimal days necessary for assessing true intake with a specified degree of error based on four season consecutive 7 day weighed diet records (WDRs).


METHODS
We evaluated consumption of energy and 30 nutrients based on four season consecutive 7 day WDRs from 80 Japanese female dietitians in 1996-1997. We examined daily, weekly, seasonal, within- and between-individual variation in nutrient intake, relative contributions of their variances to total variance, and minimal days required to estimate a person's nutrient intake within 10% and 20% of their true mean with 95% confidence intervals.


RESULTS
The relative contributions of variation for all nutrients by person were larger than those by day, week and season. Within-individual variances were greater than the between-individual variances. The ratios of within- vs. between-individual variances thus ranged from 1.3-26.9. Minimal days necessary for estimating nutrient consumption per person within 10% (20%) of the true mean with 95% confidence intervals ranged from 10-35 (3-9) days for energy and major nutrients and 15-640 (4-160) days for micro-nutrients.


CONCLUSIONS
The relative contributions of variability by person were largest for all nutrients, followed by those due to sequence of days, season and day of week. Within-individual variation was greater than between-individual variation. Minimal days necessary for ascertaining major nutrients were in general fewer than micro-nutrients.
Tokudome
Yuko
Y
Nagoya-Bunri College, Japan.
Imaeda
Nahomi
N
Nagaya
Teruo
T
Ikeda
Masato
M
Fujiwara
Nakako
N
Sato
Juichi
J
Kuriki
Kiyonori
K
Kikuchi
Shogo
S
Maki
Shinzo
S
Tokudome
Shinkan
S
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015930:Diet Records; D004046:Dietetics; D004435:Eating; D002149:Energy Intake; D005260:Female; D006801:Humans; D007564:Japan; D008875:Middle Aged; D012621:Seasons; D013997:Time Factors