Age and sex differences in variation of nutrient intakes among U.S. adults

Studies assessing associations of diet with health frequently use multi-day dietary records to estimate usual dietary intakes. We examined variation in intakes of 13 nutrients for 13,388 U.S. adults using 3 days of dietary data from the 1977-1978 Nationwide Food Consumption Survey. Ratios of within-person variability to between-person variability in intakes were large and would result in attenuated linear regression estimates of diet-health associations. For many nutrients, the magnitude of the attenuation decreased with age for both sexes but particularly for men, implying that fewer days of dietary intake per person would correctly assess diet-health associations among older adults than have been suggested for younger adults.