All types of lettuce are good for you. As a vegetable, lettuce provides fiber, vitamins, minerals and phytochemicals for very, very few calories. Lettuce is a source of folate, a B vitamin needed to make and repair DNA in cells, and vitamin K, a nutrient that makes proteins to help with blood clotting and maintaining healthy bones. You also get potassium, a mineral important for healthy blood pressure, as well as a little calcium in lettuce.
Lettuce is also a good source of two phytochemicals: beta-carotene and lutein. Beta-carotene is a powerful antioxidant, protecting cells in the body from damage caused by free radicals. In fact, its antioxidant properties are thought to help prevent certain cancers and other diseases.
Lutein is also an antioxidant that helps preserve our eyesight as we age. Once consumed, lutein makes its way to the eye where it protects the retina and lens from free radical damage. Research shows that people who have high intakes of lutein from foods are less likely to develop cataract and macular degeneration.
That said, you cannot count on all types of lettuce to be a good source of all vitamins, minerals and antioxidants. In general, lettuce that is darker green in colour is a better source of nutrients than lighter coloured lettuce
Rating of types of lettuce from most to least nutritious: Romaine, green leaf, butterhead (Boston, bibb), red leaf, and finally, iceberg.
The most nutritious lettuce is Romaine. It delivers more folate, potassium, beta carotene and lutein than other lettuces. Per one cup serving (shredded), Romaine has 2.5 milligrams of beta-carotene, 1.1 milligrams of lutein and only 8 calories. Compare that to iceberg, the least nutritious type of lettuce: one cup (shredded) contains 0.2 milligrams of beta-carotene, 0.2 milligrams of lutein and also low in calories (10 calories).
(Leslie Beck, Globe and Mail, January 31, 2012)