Brief instruments for measuring nutrition literacy - the Nutrition Health Literacy Scale and the Self-Perceived Food Literacy Scale Short Form

Abstract
Background
A healthy diet is a critical factor in maintaining long-term health. In addition to a health-promoting food environment, the nutrition health literacy (NHL) and food literacy (FL) of the population are important in this context. This paper describes the development and validation of two short instruments to measure the nutrition literacy of the population, used in the Austrian Nutrition Literacy Survey 2021.

Methods
An instrument to measure NHL (Nutrition Health Literacy Scale; NHLS) has been adapted and further developed. To measure FL, the Self-perceived Food Literacy Scale by Poelman et al. has been modified and shortened (SPFL-SF). Validation of the instruments was based on data from a web survey conducted in Austria in 2021 with almost 3,000 participants aged 18 years and older. Exploratory and confirmatory factor analyses were performed to assess the factorial validity/dimensionality of the instruments. Additionally, internal consistency was assessed using Cronbach’s alpha, ordinal alpha, and McDonald’s omega.

Results
Both instruments demonstrate excellent data-model fit. The NHLS also shows excellent internal consistency (α = 0.91), while the SPFL-SF displays a sufficient internal consistency for all (α between 0.70 and 0.89) but one sub-dimension (resisting temptation α = 0.61). Furthermore, the distribution of the items indicates that the measures are understandable and suitable, as evidenced by the absence of missing values in the sample. In addition, the items of both instruments differ in their level of difficulty or agreement.

Conclusions
The NHLS and SPFL-SF are reliable and valid instruments for measuring NHL and FL in the general adult population. The brief instruments measuring the different aspects of nutrition literacy can be easily used in nutritional or evaluation studies. Further work is required to investigate other aspects of validity.