Romaine lettuce has a lot of nutritional value and is made up of mostly water. One serving of 70 grams of lettuce has 65 grams of water and contains vitamins A, C, K, folate, potassium, and beta-carotene. Antioxidants help the body to release free radicals that can build up due to natural metabolism and environmental factors. Potassium is a mineral that helps the muscles contract normally, while vitamin A helps with eye health. Vitamin A and C can also help cholesterol from building up in the arteries.