What does "gluten-free" refer to in food products?

"Gluten-free" refers specifically to food products that do not contain gluten, which is a protein found in wheat, barley, and rye. This designation is crucial for individuals who have gluten-related disorders, such as celiac disease or non-celiac gluten sensitivity, as consuming gluten can trigger adverse health reactions in these individuals.

Understanding the meaning of gluten-free is important, particularly in the context of dietary restrictions and food labeling. The other options address different concepts that do not relate to the presence or absence of gluten in food products. For instance, lactose is a sugar found in milk and dairy products, protein content varies widely among different foods and is not an indicator of gluten presence, and calorie content pertains to the energy value of food, which is unrelated to gluten. Hence, the correct interpretation of "gluten-free" directly pertains to the absence of gluten.