On Food and Cooking

seaweed agar and carrageenan, inulin in
onions, artichokes, and sunchokes). Particular
foods offer particular kinds of fiber. Wheat
bran — the dry outer coat of the grain — is a
rich source of insoluble cellulose, while oat
bran is a rich source of soluble glucan (a
carbohydrate), and juicy ripe fruits are a
relatively dilute source of soluble pectins.
The different fiber components contribute
to health in different ways. Insoluble cellulose
and lignin mainly provide bulk to the
intestinal contents, and thus increase the rate
and ease with which they pass through the
large intestine. It’s thought that rapid
excretion may help minimize our exposure to
DNA-damaging chemicals and other toxins in
our foods, and the fiber materials may bind
some of these toxins and prevent them from
being absorbed by our cells. Soluble fiber
components make the intestinal contents
thicker, so that there is slower mixing and
movement of both nutrients and toxins. They,