Iceberg lettuce is preferred over most other types of lettuce due to its juicy crispiness. While it's true that most darker greens are richer in nutrients, iceberg lettuce is still a very healthy choice. Low in saturated fat and cholesterol (practically none) it's a good source of iron, vitamin B6, K, A, and C.
Furthermore, iceberg lettuce is high in dietary fiber, and contains traces of omega fatty acids, which is important for allover health. Folate is another benefit that iceberg lettuce provides, which helps fight heart disease.
However, iceberg lettuce is lower in vitamin C, A, iron, potassium, and calcium than darker greens. Still, it's not as if iceberg lettuce has no nutritional value at all. The juicy crispness of iceberg lettuce can make other raw veggies such as peppers, broccoli, cauliflower, or radishes more palatable.
Christopher Columbus was said to have brought lettuce to the new world. Iceberg used to be called crisphead until the 1920's when transporters began shipping it beneath a pile of ice to keep it fresh, which is how it came to be known as iceberg lettuce.
For years, iceberg lettuce has had a reputation of being low in nutrition, ranking last among other types of lettuce. In particular, iceberg lettuce was lower in potassium, calcium, phosphorous and the very last in amino acids.
Since iceberg has less nutrients than leaf lettuce, and people of today being more health-conscience, more and more are switching to leaf lettuce to maximize their vitamin and mineral intake.
Mixing greens is a good way of maintaining that moist, crispiness without sacrificing nutrition. A salad made with one part iceberg and one part romaine along with other salad veggies gives the salad a juicy crispness with the powerful antioxidants found in leaf lettuce.
When choosing lettuce for nutritional value, apparently, iceberg is at the bottom of the list, but still has a lot of healthy benefits so it shouldn't be ruled out completely. Leaf lettuce tends to be somewhat bitter, and due to the high water content of iceberg lettuce, mixing the two helps eliminate the bitterness of the leaf lettuce.
When leaf lettuce is left in the ground too long, it becomes very bitter, but even when it's harvested properly, it still retains some of the bitterness. Therefore, in order to get the most nutrition from your salads, mixing iceberg lettuce with leaf lettuce will greatly reduce the bitterness while maintaining important nutrients.