As laboratory procedures have improved, consumers now know the “dietary ﬁber” content of food, which reﬂects both soluble and insoluble ﬁber content. Today you’ll ﬁnd dietary ﬁber listed on the Nutrition Facts panel on the labels of most packaged food products.
Foods for Fiber
Do you like to nibble on popcorn? It’s a whole grain snack that helps boost the ﬁber factor in your diet. Again, dietary ﬁber comes only from plant sources of food: fruits, vegetables, legumes, grains, nuts, and seeds. Plant based foods actually contain a “mixed bag” of dietary ﬁbers, having some of both types: soluble and insoluble. Good sources of soluble ﬁber may supply some insoluble ﬁber, too, and vice versa. For example, fruits and vegetables have both pectin (soluble) and cellulose (insoluble). However, fruit usually has more pectin; vegetables, more cellulose. Both oatmeal and beans have some of both: soluble and insoluble ﬁber. (Beta glucan is the soluble ﬁber in oats and barley.)
Here are some speciﬁc foods that provide signiﬁcant amounts of insoluble and soluble ﬁbers. Their texture is a clue to their presence.
- Insoluble ﬁbers: whole wheat products; wheat, oat, and corn bran; ﬂaxseeds; and many vegetables (such as cauliﬂower, green beans, and potatoes), including the skins of fruits and root vegetables, and beans. In fact, their tough, chewy texture comes from insoluble ﬁbers.
- Soluble ﬁbers:dried beans and peas, oats, barley, ﬂaxseeds, and many fruits and vegetables (such as apples, oranges, and carrots). When they’re cooked, the soft, mushy texture comes from their soluble ﬁbers. Psyllium seed husks also supply soluble ﬁber.
For the record: Any nondigestible carbohydrate in animal-based foods is not currently deﬁned as “dietary ﬁber” on food labels. But stay tuned in the future for possible changes in ﬁber labeling on food.
From grain to grain, brans aren’t all alike. The bran layers in different grains—wheat, rice, corn, oats, and others have varying types and different amounts of ﬁber. Wheat bran, for example, has a higher concentration of ﬁber than most other bran, and its bran is mainly insoluble. To compare, oat bran contains mainly soluble ﬁber.
The ﬁber content of vegetables and fruits varies; some are better sources than others. A heaping bowl of fresh lettuce greens may seem loaded with ﬁber. However, one cup of lettuce contains just about 1 gram of ﬁber; instead, it’s mostly water. In contrast, 1⁄2 cup of a three-bean salad (mainly legumes) supplies more than 3 ﬁber grams.
Food preparation or processing may alter the ﬁber content of foods. Just as a sponge changes in its ability to hold water when it’s chopped into very ﬁne pieces, so properties of ﬁber may change a bit when the structure is altered by food processing or preparation. Fiber content drops, too, when the ﬁber rich part of a food is removed.
When it comes to making food choices, don’t get hung up on which ﬁber is which—just consume enough overall. By adding a variety of ﬁber-rich foods to your meals and snacks, you usually get the health beneﬁts of both soluble and insoluble ﬁbers.