Commercial portion-controlled foods in research studies: how accurate are label weights?

Objective: The purpose of this study was to evaluate the reliability of label weights as surrogates for actual weights in commercial portion-controlled foods used in a research setting.

Design: Actual weights of replicate samples of 82 portion-controlled food items and 17 discrete units of food from larger packaging were determined over time. Comparison was made to the package label weights for the portion-controlled food items and the per-serving weights for the discrete units.

Setting: The study was conducted at the US Department of Agriculture's Beltsville Human Nutrition Research Center's Human Study Facility, which houses a metabolic kitchen and human nutrition research facility.

Main Outcome Measures: The primary outcome measures were the actual and label weights of 99 food items consumed by human volunteers during controlled feeding studies. Statistical analyses performed The difference between label and actual weights was tested by the paired t test for those data that complied with the assumptions of normality. The Wilcoxon signed rank test was used for the remainder of the data. Compliance with federal guidelines for packaged weights was also assessed.

Results: There was no statistical difference between actual and label weights for only 37 food items. The actual weights of 15 portion-controlled food items were 1% or more less than label weights, making them potentially out of compliance with federal guidelines.

Conclusions: With advance planning and continuous monitoring, well-controlled feeding studies could incorporate portion-controlled food items and discrete units, especially beverages and confectionery products. Dietetics professionals should encourage individuals with diabetes and others on strict dietary regimens to check actual weights of portion-controlled products carefully against package weights.