Pm. Guenther et al., SEPARATING FACT FROM ARTIFACT IN CHANGES IN NUTRIENT INTAKE OVER TIME, Journal of the American Dietetic Association, 94(3), 1994, pp. 270-275
Objective To determine whether the differences between the procedures
and nutrient databases used in the 1977-1978 Nationwide Food Consumpti
on Survey (1977-78 NFCS) and those used in the 1987-88 NFCS could nota
bly affect the estimated mean nutrient intakes. Design This was a spli
t-sample field experiment. Seventy-two area segments were randomly sel
ected; 10 housing units were selected in each segment and randomly ass
igned to one of two experimental groups. Setting The study took place
in the Philadelphia, Pa, metropolitan area. Subjects The subjects were
697 women aged 20 to 49 years. Treatment Group A was interviewed usin
g 1987-88 NFCS 24 hour recall procedures and their nutrient intakes we
re calculated using the 1987-88 NFCS food codes, weight conversion fac
tors, and nutrient database. Group B was interviewed using 1977-78 NFC
S 24-hour recall procedures and nutrient intakes were calculated four
ways using various combinations of 1987-88 and 1977-78 NFCS food codes
, weight conversions, and nutrient database. Main outcome measure Mean
intakes of food energy and 14 nutrients were calculated. Statistical
analysis We used two-sample, multivariate t tests; univariate t tests;
univariate repeated measures analysis of variance; and univariate pai
red t tests. Results Changes in the nutrient database caused by improv
ed analytic techniques and increased number of foods sampled were grea
t enough to warrant revising the 1977-78 NFCS estimated intakes for ir
on, magnesium, and vitamins B-6 and B-12. Changes in intake of fat, vi
tamin A, and thiamin, however, were caused by real changes in foods so
no revisions were necessary for these nutrients. Other nutrients were
unaffected. Conclusion When considering changes in nutrient intake ov
er time, it is important to correct the earlier food composition estim
ates so that they accurately reflect the composition of foods at the t
ime they were consumed. This requires preserving the real differences
in the composition of foods while correcting for artifactual differenc
es attributable to improvements in the quality of nutrient data.