Actual suspected caloric difference is minimal, after all, well, it is seaweed, not a very dense food stuff. :)

I'm not going to link to antibiotics causing gut flora problems, it is well known and responsible doctors actually can prescribe a nice little compact pill full of gut bacteria that replaces the ones wiped out as a side effect of antibiotics.

The stuff about a biased diet messing up gut bacteria is also hard to find research on (I've read it, but it is a PITA to find again). Basically different bacteria specialize in breaking down different types of food. If you have a diet lacking in some major food group, that stock of bacteria runs low.

Vegans can have this issue if they go back to eating meat. There is typically some tiny supply of the needed bacteria left and the population is restored after awhile, but the initial few hamburgers can be somewhat uncomfortable.