When I was in the middle of my Whole30 (a month and half ago!) I wrote to Five Guys about their ingredients. Even though they have their nutritional info online, I grilled them (no pun) about any hidden ingredients that might now have been mentioned. I just now heard back from them. Here's what they said:
Since 1986 Five Guys has focused on serving the freshest product in the simplest way possible. We do not add
anything to our products. Our burgers are NOT seasoned, they are simply 80/20 ground beef, our mushrooms
are sauteed on a flat top grill as they are with NO oil or butter. Our produce is cut fresh daily and does not have
anything added to it as well. In fact, our nutritional information is located on website www.fiveguys.com if you
would like you can also find the Five Guys story located under the About us tab.
So, in the case of Five Guys, if you are willing to have a hamburger patty on a lettuce "bun" with just vegetables of various sorts as condiments, sounds like they would be legal in the Whole30 world. Since finishing the Whole30, I've been glad that I did this sort of research. I'm not eating out nearly as much, but when I do, I often just go paleo for that meal and that helps me feel like I'm not eating a bunch of garbage just because I'm eating out.