The high prevalence and associated medical costs of obesity in the United States necessitate optimizing obesity treatment, typically through comprehensive lifestyle interventions. These interventions target excess energy intake and low physical activity, focusing on factors like high energy-dense foods, large portion sizes, sugar-sweetened beverages, food variety, and unreliable nutrition information. Successful programs teach nutrition concepts, cognitive behavior principles, and promote physical activity, typically evaluating success primarily on weight loss. However, there's been no systematic assessment of whether participants adequately understand the nutritional knowledge component of these programs. Previous studies have used general nutrition knowledge tools instead of those specific to weight management. This lack of success in weight loss may result from insufficient teaching of key nutrition principles or failure to implement behavior change skills. The researchers hypothesized that understanding core concepts is more effective than memorizing facts, allowing application to novel situations. A dedicated questionnaire focusing on key dietary principles would help programs evaluate the effectiveness of their nutrition education. While nutrition knowledge doesn't guarantee long-term weight loss, the knowledge, attitude, and behavior model suggests that knowledge is essential for successful behavior change. A literature review found no validated instruments assessing dietary principles specific to weight management, motivating the development of the Weight Management Nutrition Knowledge Questionnaire (WMNKQ).

A PubMed search using keywords "nutrition" or "nutritional," "knowledge," and "questionnaire" or "survey" revealed a lack of validated instruments specifically testing dietary principles for weight management. Existing validated instruments assessed general nutrition knowledge, not the specific concepts crucial for effective weight management. This gap in research highlighted the need for a new instrument focused on the key nutrition principles relevant to successful weight loss.

The WMNKQ development involved creating an initial pool of approximately 200 questions from existing questionnaires (Parmenter and J Wardle Questionnaire, NHLBI, CDC, Mayo Clinic Patient Education Center, and USDA) and newly written items. These questions were designed to assess the understanding of concepts, not just isolated nutrition facts. The focus areas were energy density, portion size, alcoholic and sugar-sweetened beverages, the impact of food variety, and reliable nutrition information sources. The questionnaire was designed for a 9th-grade reading level using the Flesch-Kincaid readability test. The item pool was refined to 60 questions after eliminating redundant or complex items. Face validity was assessed by six nutrition experts (PhD or MD scientists and registered dietitians), who provided feedback for modifications, elimination, and/or additions, resulting in 57 items. Quantitative assessment involved 286 adults (187 from Olmsted County, MN, and 99 from Duval County, FL) completing the 57-item questionnaire. Construct validity used the known-groups method comparing 18 registered dietitians and 25 IT specialists. Test-retest reliability was assessed using the same groups two weeks apart. Criterion validity was assessed using a nutrition knowledge intervention (three 1-hour classes) with 119 Olmsted County participants, measuring pre- and post-intervention scores. Convergent validity examined correlations between scores and demographics (age, education) in 126 participants. Statistical analyses included item difficulty analysis, item discrimination (item-total score correlation), inter-item correlation, Cronbach's alpha for internal consistency, Spearman's correlation for test-retest reliability, independent t-tests, analysis of covariance (ANCOVA), and paired t-tests. The scoring system used a percentage correct and a weighted score system prioritizing energy density and portion size questions.

The final WMNKQ comprised 43 items after refining the initial 60 based on expert feedback and quantitative analysis. Nine items were excluded due to item difficulty (answered correctly by >90% or <30% of participants). Four items failing item discrimination criteria were retained because they addressed important concepts. The WMNKQ demonstrated excellent internal consistency (Cronbach's alpha = 0.88) and test-retest reliability (correlation = 0.90, P < 0.0001). Construct validity was supported by dietitians scoring significantly higher (16%, p < 0.0001) than IT specialists. Criterion validity was confirmed by a significant improvement in knowledge scores (11.2%, 95% CI 9.8-12.5, p < 0.0001) after the nutrition intervention. Convergent validity was shown through younger participants (<55 years) scoring significantly better than older participants.

The WMNKQ successfully addresses the need for a validated instrument to assess weight management-specific nutrition knowledge. Its strong psychometric properties (reliability and validity) make it a valuable tool for evaluating the effectiveness of nutrition education components in weight management programs. The significant improvement in scores after the intervention demonstrates that the questionnaire is sensitive to changes in knowledge. The findings support the use of the WMNKQ for assessing nutrition knowledge and evaluating intervention programs, potentially leading to better-targeted interventions and improved weight management outcomes.

The WMNKQ is a reliable and valid instrument for measuring weight management nutrition knowledge. Its use will allow researchers and practitioners to evaluate the effectiveness of their interventions and identify areas where nutrition education needs to be improved. Future research could explore the predictive validity of WMNKQ scores in terms of long-term weight loss success and its applicability across diverse populations.

The study's limitations include the sample demographics, which may limit the generalizability of the findings to other populations. The specific intervention used to assess criterion validity might not be representative of all weight management interventions. The cross-sectional nature of some analyses limits causal inferences. Further research is needed to assess the WMNKQ's validity across a broader range of ages, ethnicities, and socioeconomic backgrounds.