Paying for protein: protein-named US packaged foods, nutrients and breakeven prices

US evidence on what protein-marketed foods contain and what their protein costs rests mostly on proprietary data. Using USDA FoodData Central Branded Foods (April 2026 release; 462,142 current US products), I compared 6,011 products with "protein" in their name, brand or sub-brand against 192,025 other products in the same 34 categories and with 594 same-brand lines. In a hand-coded sample, 98.7% of names were protein-content messages. Of protein-named products, 88.2% declared at least 10 g of protein per labelled serving, yet they were only 20.3% of products that did. Within categories, protein-named products had 22.9 g more protein per 100 g, 3.6 g less added sugar and 34 mg more sodium per 100 kcal, and more often contained non-sugar sweeteners (58.4% vs 7.7%), confirming German and Spanish findings; within brand lines the differences were smaller but mostly in the same direction. At 2025–2026 Bureau of Labor Statistics prices, dried beans, eggs, whole milk and boneless chicken breast supplied 10 g of protein for US$0.17–0.41. Product-specific breakeven prices, at which a product's protein would cost the same as from the median of these foods, had a median of US$0.49 per serving (interquartile range across products 0.36–0.65). At GroceryDB's 2021 shelf prices, 94.9% of protein-named items exceeded that cost per gram of protein. In the median brand line, protein-named products carried 1.66 times the protein per 100 g, so a premium below 66% would still lower their cost per gram of protein. The label marks real protein; cheap protein is in staples. Preprint, not peer reviewed. Also published at https://x9m8.com/protein-marketed-foods/. The zip file contains the code, results and the two independent audits.