Variability in nutrient intake in a 28-day period.

This study of food logs showed that although individual intake varied widely, there were no significant differences in the intake of energy or seven selected nutrients from week to week over a four-week period. With the exception of protein, there was no difference attributable specifically to the day of the week. Thus, it is concluded that 7-day records most accurately reflect intake over periods of up to 28 days. A 4-day record, covering a weekend (Friday through Monday), also correlates well with information collected for 7, 14, and 28 days.