Iceberg, also called head, lettuce contains only trace amounts of nutrients and fiber. Because it's one-half water, it is low in calories.
Iceberg lettuce is the least nutritious member of the lettuce family.
Dark leafy greens have more nutrients, including vitamin C, folic acid and beta-carotene. Chlorophyll pigment that makes these vegetables green hides the yellow color of carotene. The darker green the leaf, the more beta-carotene. Among greens, spinach is one of the highest in vitamin C and beta-carotene. For lettuce, pick romaine.