Smashburger publishes real ingredient statements through their allergen widget, and they show soybean oil first in every mayo and sauce and in five of six buns, with the fries naming six different seed oils at once. The default Classic Bun carries Yellow 5, Yellow 6, Red 40 and propylparaben, and the standard ketchup and Smash Sauce both contain high fructose corn syrup, so the additives are in the default build rather than in optional extras.
Rated 2026-09-02 from Smashburger's own live ingredient data, pulled through the BigZpoon widget linked from their allergen page - about 30 components with verbatim manufacturer statements. Seed oil is everywhere the beef is not. Soybean oil is the FIRST ingredient in the Mayo, Chipotle Mayo, Truffle Mayo, Smash Sauce and Ranch, and it is in 5 of the 6 buns. The fries name six in one line: "Potatoes, Vegetable Oil, Canola Oil, Sunflower Oil, Cottonseed Oil, Palm Oil, Corn Oil, Soybean Oil, Hydrogenated Soybean Oil...". The clean exceptions are real but narrow - ketchup, mustard and BBQ sauce carry no oil, and the patty is "100% Pure Ground Beef, Salt, Spice...". Additives are scored all rather than some because they sit in the DEFAULT build: the Classic Bun, used on the burger and the chicken sandwich, lists "FD & C Yellow #5, Yellow #6, Red #40" and propylparaben, and the standard ketchup and Smash Sauce both list high fructose corn syrup.