Checking Google as for the nutrition of lettuce, I found the following:

Wikipedia:

Lettuce is a fat free, low calorie food and is good for a well balanced
diet. It is a valuable source of vitamin A and folic acid. Lactucarium (or
“Lettuce Opium”) is a mild opiate-like substance that is contained in all
types of lettuce. Both the Romans and Egyptians took advantage of this
property eating lettuce at the end of a meal to induce sleep.

On http://www.doleeurope.com/tabid/200/Default.aspx you will find detailed
information about the contents of iceberg lettuce.

There is more information in the internet. Just check "iceberg lettuce". It
is that simple.

Regina
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www.an-kreta.de/
Cruelty against animals is one of the most denotable characteristics
of an inferior and ignoble nation. (Alexander von Humboldt)