Since the 90's the myth has been spread that iceberg lettuce has no nutritional value. This is actually false:
For as little as 10 calories a serving is gives you a ton of stuff including folate (a B vitamin), vitamin B6, vitamin K, vitamin A, vitamin C, and thiamine. It’s made up mostly of water (which is actually a good thing) and dietary fiber providing necessary roughage for our digestive system. It’s alkaline, clarifies your blood, and a nerve strengthener. It also contains the the cancer fighting carotenoids lutein and zeaxanthin. Iceberg lettuce has been linked to preventing cancer better than any other lettuce (for some reason the body more readily uses the cancer fighting vitamins from iceberg than other sources) Yes mixing your lettuces is your best bet, but iceberg does have it's place in a healthy diet.