Inulin
Inulins are a group of naturally occurring
oligosaccharides (several simple sugars linked together) produced by many types of plants. They belong to a class of carbohydrates known as
fructans. Inulin is used by some plants as a means of storing energy and is typically found in
roots or
rhizomes. Most plants which synthesize and store inulin do not store other materials such as
starch.
Inulin is used increasingly in foods, because it has excellent nutritional and functional characteristics. It ranges from completely bland to subtly sweet and can be used to replace sugar, fat, and flour. This is particularly advantageous because inulin contains one-third to one-fourth the
food energy of sugar or other carbohydrates and one-sixth to one-ninth the food energy of fat. It also increases
calcium absorption (PMID 16087995) and possibly
magnesium absorption (PMID 12514257), while promoting
probiotic bacteria. Nutritionally, it is considered a form of
soluble fiber, and it is important to note that consuming large quantities (particularly for sensitive and/or unaccustomed individuals) can lead to gas and bloating. Inulin has a minimal impact on
blood sugar, making it generally considered suitable for
diabetics and potentially helpful in managing blood sugar-related illnesses.
Inulins are
polymers mainly comprised of
fructose units and typically have a terminal
glucose. The fructose units in inulins are joined by a
beta-(2-1) glycosidic link. Plant inulins generally contain between 2 to 140 fructose units. The simplest type of inulin is 1-
kestose, which has 2 fructose units and 1 glucose unit.
Inulins
with a terminal glucose are known as
alpha-D-glucopyranosyl-[beta-D-fructofuranosyl](n-1)-D-fructofuranosides, abbreviated as
GpyFn. Inulins
without glucose are
beta-D-fructopyranosyl-[D-fructofuranosyl](n-1)-D-fructofuranosides, abbreviated as
FpyFn where
n is the number of fructose residues and
py is the abbreviation for
pyranosyl.
Hydrolysis of inulins may yield
oligofructose, which are polymers with a
degree of polymerization (DP) of <= 10.
Inulin is indigestible by the human
enzymes
ptyalin and
amylase, which are designed to digest starch. As a result, inulin passes through much of the
digestive system intact. It is only in the
colon that
bacteria metabolise inulin, with the release of significant quantities of
carbon dioxide and/or
methane. Inulin-containing foods can be rather
gassy, particularly for those unaccustomed to inulin, and these foods should be consumed in moderation at first. However, given some time, most people can adapt to consuming fairly high levels of inulin without side effects.
Inulin is not broken down into simple sugars (
monosaccharides) by normal
digestion, so it does not elevate blood sugar levels, hence, helping diabetics regulate blood sugar levels.
Inulin is also a highly effective
prebiotic, stimulating the growth of beneficial
probiotic bacteria in the
gut. As mentioned, inulin passes through the
stomach and
duodenum undigested and is highly available to the gut bacterial flora. This contrasts with proprietary probiotic formulations based on
yogurt or
milk in which the bacteria have to survive very challenging conditions through the gastrointestinal tract before they are able to colonize the gut.
Some traditional diets contain up to 20g per day of inulin or oligofructose.Many foods naturally high in inulin or oligofructose, such as
chicory,
garlic, and
leek, have been seen as "stimulants of good health" for centuries (PMID 10395609).
Inulin can be found in commerically available products such as
Fibersure from the Makers of
Metamucil. Fibersure is a fiber supplement powder that can be added to foods or beverages without changing the taste or texture. It performs well in cooking and baking applications and can be an easy way to add additional fiber to the diet through foods and drinks.
The
New England Journal of Medicine has reported on allergic reactions to inulin in foods [
1]. This article documents the case of one adult male with a severe allergy to inulin [
2].
Plants that contain high concentrations of inulin include:
*
Dandelion (
Taraxacum officinale)
* Wild Yam (
Dioscorea sp.)
*
Jerusalem artichokes (
Helianthus tuberosus)
*
Chicory (
Cichorium intybus)
*
Jicama (
Pachyrhizus erosus)
*
Burdock (
Arctium lappa)
*
Onion (
Allium cepa)
Inulin, as it is completely filtered at the
glomerulus and is neither secreted nor reabsorbed in the
tubules, has been used as an important medical test of
renal function, specifically a measure of
glomerular filtration rate. The measurement of GFR by inulin is still considered the gold-standard, although it has been now largely replaced by other, simpler measures that are actually estimations of GFR, which have been confirmed in large cohorts of patients with
chronic kidney disease (e.g.
Iothalomate,
EDTA,
creatinine clearance).
*
Cargill's Inulin Homepage*
Orafti, a Major Inulin Manufacturer*PMID 15877886 - Introducing inulin-type fructans.
