My DietPower software says that shredded romaine lettuce has 1.3 grams of carbs per cup. But, 1.0 grams of that is fiber leaving a net effective carb count of about 0.3 grams per cup. So, I'd say that you can eat a lot of lettuce without much of a blood sugar effect. (At least, I never seem to notice low carb salads affecting mine.)