I've never heard the wet lettuce expanding thing before, that's a new one on me. Bread, toast and rice are often thought by some to have that effect, and likewise readily ignored by others to little effect. But this early out you should be taking things slowly and following your doc's advice.
Some people do have a problem with lettuce for some reason, even many months out (and, as usual, many others have no problem at all - a big YMMV thing.) I generally use chopped raw spinach rather than lettuce due to its somewhat better nutritional profile, but haven't had any particular problem with lettuce when I have had restaurant salads (I just don't eat much of it since they use it as filler instead of the more expensive and nutritious vegetables and Proteins.)
My surgeon said only cooked spinach for now. I just finished my final phase so now I'm on unrestricted, but I still can't have raw fruits and veggies or nuts. don't know when he'll clear me for that.
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