Final answer:
A 24-hour dietary recall is the most appropriate and practical method to assess nutritional risk in elderly participants at a health fair, as it helps identify dietary habits and nutrient deficiencies.
Step-by-step explanation:
The most appropriate assessment method for evaluating nutritional risk in elderly participants at a health fair is a 24-hour dietary recall. This non-invasive method involves asking individuals to recall all the food and beverages they have consumed over the past 24 hours. It provides an overview of the participant's dietary habits and potential nutrient deficiencies without requiring specialized equipment or training, which makes it practical for a health fair setting. Other methods like BMI, triceps skin fold thickness, and midarm muscle circumference may require more technical skill, may not be as practical in a community setting, and they may not be as accurate in the elderly due to changes in body composition with age.