A type of carbohydrate or starch that your body cannot digest, dietary fiber exists only in plant foods. It regulates your digestion, sweeping out the intestines and adding bulk to your stool. Fruits, whole grains and vegetables, including lettuce, are sources of fiber. The fiber in lettuce is both soluble and insoluble.
Soluble Vs. Insoluble Fiber
Two types of fiber are found in plant products: soluble and insoluble. Plant cells contain water-soluble fibers, meaning they dissolve in water to become a soft gel. Soluble fiber helps your body by binding with cholesterol and removing it from your bloodstream. It can also help firm your stool and slow digestion to keep blood sugar levels more stable. Insoluble fiber passes quickly through your gut, preventing constipation and gut infections. By warding off constipation, it can also help prevent hemorrhoids. Find insoluble fiber primarily in fruit with edible skins, raw vegetables, nuts, beans and whole grains.
Types of Soluble Fiber
Soluble fiber can further be broken down into types: beta-glucan, found mainly in grains; pectin, sugar acids mainly found in fruit and sweet vegetables; natural gums, including guar, locust bean, gum acacia, carrageenan and xanthan; and inulin, present in onions, chicory and wheat. Radicchio lettuce is rich in inulin, while butter lettuce is not. Other lettuces may contain some pectin and inulin, but the exact ratios depend on the type.
Lettuce as Fiber
Lettuce isn't high in fiber when compared to other produce. Romaine lettuce, for example, contains 1.2 grams of fiber per cup, while iceberg has only 0.7 gram per cup. Compare this to higher-fiber options, such as a pear with 5.1 grams, 1 cup of green beans with 4 grams or half of a sweet potato with 3.9 grams. The National Academy of Nutrition and Dietetics recommends you get between 20 and 35 grams of fiber per day from a variety of sources to promote good health.
Most people should seek to eat more fiber, of any kind, to promote good digestive health. However, those who experience certain digestive disorders, including irritable bowel syndrome or Crohn's disease, may shy away from fiber altogether. They also may find that certain types of fiber, such as inulin, cause their symptoms to intensify, so they need to avoid it. Unfortunately, determining your trigger foods is individual; some lettuces may cause digestive distress, while others are perfectly digestible for you. A food diary may help you identify your personal triggers; sometimes it isn't the lettuce in a salad you've eaten that's caused a problem but other vegetables that you've added.