There is a lot of hype with nutritionists about iceburg lettuce right now. They always seem to have anxiety about some food or another. At one point it was declared that potato skins were toxic and no human should eat them.
A couple years later, they learned that they are not toxic and never were.
Right now, nutritionists say that iceburg lettuce is completely void of any nutritional value. God made it, so it's not useless. I'm sure they'll change their minds in a couple of years.
Meanwhile, piggies like other mammals, need a variety in their diet. Iceburg lettuce is fine, but not solo. We get a salad mix for out piggies, with leaf lettuce, spinach, iceburg, romaine, and other green leafy veggies. Then we also give them a bit of whatever else we have on hand: zucchini, cucumber, squash, carrot, etc. For a very special treat, we give them a little orange or apple when we hold them.