Food scientists use sophisticated equipment to determine levels of vitamins, fat, sugar, protein and other nutrients in food. Luckily, you don't have to live next door to one of these experts to compare one lettuce to another. The United States Department of Agriculture (USDA) maintains a database -- the USDA National Nutrient Database for Standard Reference -- that makes it possible to find all of the key nutrients in various foods. The table shows the results for the four main types of lettuce:
As the USDA database and our abbreviated table make clear, not all lettuces are created equal. Iceberg lettuce, which is by far the most popular lettuce in the United States, delivers the least nutritional bang for the buck. Although it has more fiber than some lettuces, it's a bit of a dud when it comes to vitamin and mineral content. And it's high in sugar, which is a major source of calories.
Romaine lettuce is a better choice. Romaine has less sugar and more fiber. But it really excels in the vitamin and mineral departments. It's an excellent source of vitamin C and a good source of folate and vitamin A. It also provides 10 times more beta carotene than iceberg lettuce and almost as much as spinach. All of this combines to make romaine one of the healthiest of all the lettuces.
Green-leaf lettuce is a solid runner-up. It's low in fat and sugar and high in protein. It also delivers decent amounts of calcium, phosphorous, potassium, manganese and vitamins C, A and K. Red-leaf and butterhead lettuces aren't slouches either, as they surpass iceberg varieties in almost every nutrient category and have the highest amount of iron of all lettuces.
So if you really want to stay strong to the finish, stick with romaine and the other dark green leafy lettuces while cutting back on the crispheads. And don't forget to spice things up with the more exotic members of the family, such as arugula, curly endive, escarole and radicchio.