Come on. I've never heard (no one has) the phrase, "don't eat lettuce". I've heard don't eat processed carbs, don't eat bread, don't eat pasta, don't eat simple sugars, don't eat potatoes.
If all you read about low-carb diets is the first paragraph about any popular news story about them, then what you know is that low-carb diets are the ones where you can eat lots of meat and you should shun any foods with sugar or starches.