Bread[especially white] is digested vary fast by the body. Making a sanwich is pretty much like pouring table sugar over your meat and veggies.
Okay, so a sandwich with whole grain bread then.
And the difference in white bread versus whole grain bread is relatively small in terms of glycemic index — 30 to 40 percent. IOW whole grain is 60 to 70 percent as evil as white bread.
Yet people have been eating bread since forever and it didn’t seem to wreck their health or make them fat until recently. So it must not be the bread that’s the problem, which means sandwiches aren’t a problem either.