Adjustment Factors Can Improve Estimates of Food Group Intake Assessed Using a Short Dietary Assessment Instrument

Abstract

Background: Methods to address misreporting associated with short dietary assessment instruments are needed.

Objective: Our objective was to develop and evaluate the direct and indirect validity of adjustment factors applied to a short dietary assessment instrument to improve estimates of usual consumption of core and discretionary food and beverage intake.

Design: Validation of the Short Food Survey relative to 24-hour recalls was performed. The Short Food Survey requires individuals to report their usual intake of fruit, vegetables, grains, meat, dairy, and discretionary choices in multiples of standard servings. Adjustment factors were developed based on a ratio (usual portion size estimated from national data to standard serving size). The estimates of food group intakes (unadjusted and adjusted) were compared to 24-hour recalls.

Participants/setting: Three population samples were used in this study. The direct validation used data from 61 Australian adults (collected 2013-2014). The indirect validation compared data from the 2011-2013 Australian National Nutrition and Physical Activity Survey (n=9,435) to a sample of 145,975 who completed the Short Food Survey in a format that is freely available online (2015-2016).

Main outcome measures: Food group intake (in servings) was measured.

Statistical analyses performed: Descriptive and inferential statistical analyses were conducted.

Results: Direct validation showed the adjustment factors improved the survey-derived estimates of intake for all food groups except grain foods. For grains, the mean difference went from -0.6 servings to +1.2 to 1.5 servings. The absolute difference in food group intake between the adjusted Short Food Survey and recalls remained statistically significant for fruit, meat, dairy, and grains, but was not different for vegetables and discretionary foods. The indirect validation showed that the adjusted estimates of intake from the online Short Food Survey were closer to the population estimates reported by 24-hour recall for all food groups except meat.

Conclusions: Adjustment factors can improve estimates of food group intake assessed using a short dietary assessment instrument for some but not all food groups.

Keywords: Food intake; Misreporting; Short dietary instrument; Statistical adjustment; Surveillance.