Development and validation of a short food questionnaire to screen for low protein intake in community-dwelling older adults: The Protein Screener 55+(Pro55+)

In old age, sufficient protein intake is important to preserve muscle mass and function. Around 50% of older adults (65 + y) consumes <= 1.0 g/kg adjusted body weight (BW)/day (d). There is no rapid method available to screen for low protein intake in old age. Therefore, we aimed to develop and validate a short food questionnaire to screen for low protein intake in community-dwelling older adults. We used data of 1348 older men and women (56-101 y) of the LASA study (the Netherlands) to develop the questionnaire and data of 563 older men and women (55-71 y) of the HELIUS study (the Netherlands) for external validation. In both samples, protein intake was measured by the 238-item semi-quantitative HELIUS food frequency questionnaire (FFQ). Multivariable logistic regression analysis was used to predict protein intake <= 1.0 g/kg adjusted BW/d (based on the HELIUS FFQ). Candidate predictor variables were FFQ questions on frequency and amount of intake of specific foods. In both samples, 30% had a protein intake <= 1.0 g/kg adjusted BW/d. Our final model included adjusted body weight and 10 questions on the consumption (amount on average day or frequency in 4 weeks) of: slices of bread (number); glasses of milk (number); meat with warm meal (portion size); cheese (amount and frequency); dairy products (like yoghurt) (frequency); egg(s) (frequency); pasta/noodles (frequency); fish (frequency); and nuts/peanuts (frequency). The area under the receiver operating characteristic curve (AUC) was 0.889 (95% CI 0.870-0.907). The calibration slope was 1.03 (optimal slope 1.00). At a cut-off of <= 0.8 g/kg adjusted BW/d, the AUC was 0.916 (96% CI 0.897-0.936). Applying the regression equation to the HELIUS sample, the AUC was 0.856 (95% CI 0.824-0.888) and the calibration slope 0.92. Regression coefficients were therefore subsequently shrunken by a linear factor 0.92. To conclude, the short food questionnaire (Pro(55+)) can be used to validly screen for protein intake <= 1.0 g/kg adjusted BW/d in community-dwelling older adults. An online version can be found at www.proteinscreener.nl. External validation in other countries is recommended.