Front-of-package protein labels are frequently added to breakfast cereals, aimed at increasing purchases by consumers who believe they would benefit from eating more protein. However, the overall nutritional compositions of such products are often not significantly better than similar products without protein labels, and may contain more sugar, sodium, and calories to improve taste. We conducted an online survey with 1022 US adults to examine consumer perceptions of two cereals (Special K Original and Special K Protein). Participants perceived Special K Protein as healthier and more nutritious, though less tasty, than Special K Original. Special K Protein was perceived as providing greater health benefits, such as being more likely to help them build muscle, stay healthy, and live longer. Many participants perceived no differences in the amounts of certain nutrients between the cereals, such as sugar (54.5%), sodium (59.2%), and calories (49.1%). Yet, when serving sizes are equalized to one cup, Special K Protein has more sugar, sodium, and calories than Special K Original. Though most participants reported viewing the Facts Up Front label, only 21.3% correctly chose Special K Original as having the larger serving size. This pattern of results suggests the presence of a health halo surrounding the protein-labeled product.