Larch arabinogalactan refers to a polysaccharide derived from wood of the Western larch or Larix occidentalis. Arabinogalactans occur in other types of larch, but that which is marketed for supplemental usage comes from the Western larch. Larch arabinogalactan is not one substance but a mixture of several different arabinogalactans with molecular weights as low as 3,000 daltons and as high as 100,000 daltons.
Arabinogalactans are water-soluble polysaccharides widely found in plants, fungi and bacteria. They are comprised of D-galactose and L-arabinose residues in the form of a beta-D-(1-3)-galactan main chain with side chains made up of galactose and arabinose units of various lengths. Galactan itself is a polymer of galactose.
In plants, arabinogalactans occur as arabinogalactan proteins. These proteins are proteoglycans involved in plant growth and development; they may also be involved in signal transduction in plants.
As produced, Larch Arabinogalactan is a dry, free-flowing powder, with a very slight pine-like odor and sweetish taste. It is 100% water-soluble and produces low viscosity solutions. Because of its excellent solubility and mild taste, the powder mixes readily in water and juices and is easily administered (even to children).
The longest recognized use of Larch Arabinogalactan is probably as a source of dietary fiber. It has been shown to increase the production of short-chain fatty acids (SCFA's), principally butyrate and proprionate. These special fatty acids are critically important for the health of the colon. In fact, having an adequate supply of SCFA's is thought to make colon cells more resistant to both tumor promotion and a variety of intestinal disease.
Larch Arabinogalactan also acts as a food supply for friendly bacteria. The term used to describe this action is "prebiotic". The most well known prebiotic substance is "fructooligosaccharides" or "FOS". Larch Arabinogalactan acts in the same manner as FOS in humans. In effect, when we consume Larch Arabinogalactan, we are rewarded by this significant positive effect on our gut microfloral balance.
Specifically, this fiber acts to increase good bacteria like bifidobacteria and lactobacillus, while decreasing bad bacteria. Since these friendly bacteria are critically important for the health of our digestive and immune systems, detoxification and hormone regulating capabilities, and nutrient formation and absorption; the growth promoting effects of larch Arabinogalactan on these organisms alone makes it a valuable addition to our diet.
Arabinogalactan appears to be a synergistic immunomodulator  with fucoidin, the sulphated polysaccharide from Fucus vesiculosis (Bladderwrack)