Rhamnose sugar by Ray Sahelian, M.D.
February 12 2016

Rhamnose is a natural sugar. Rhamnose has been thought to be an inert sugar not metabolized by the human body. However, while conducting an investigation on gut permeability in children undergoing cardiac surgery, increased concentrations of rhamnitol were found in the urine samples. Therefore, rhamnose is probably not an inert sugar and appears to be partially metabolized into rhamnitol by the human body. If you have an interest in having a natural sugar substitute without calories, consider stevia for more information.

As of 2016, I am not aware of more than a couple of human study with rhamnose supplements.

Where does L-Rhamnose come from?
L-Rhamnose can be isolated from Buckthorn (Rhamnus) and poison sumac. Rhamnose is also found as a glycoside in a variety of other plants.

Pharmacological properties of rhamnose-rich polysaccharides, potential interest in age-dependent alterations of connectives tissues.
Pathol Biol (Paris). 2006. Laboratoire de recherches ophtalmologiques, Hôtel-Dieu, université Paris-V, 1, place Parvis-Notre-Dame, Paris cedex, France.
Rhamnose -rich oligo- and polysaccharides were tested for their potential pharmacological properties using human skin fibroblasts in serial cultures. The substances tested were shown to stimulate cell proliferation, decrease elastase-type activity, stimulate collagen biosynthesis, and protect hyaluronan against free radical mediated degradation. These reactions appear to be triggered by the mediation of a specific alpha-L-rhamnose recognizing lectin-site acting as a receptor, transmitting signals to the cell-interior. The rapid increase of intracellular free calcium after addition of Rhamnose -rich oligo- and polysaccharides and preliminary data using micro arrays appear also to confirm this contention.

J Nutr. 2006. L-rhamnose and lactulose decrease serum triacylglycerols and their rates of synthesis, but do not affect serum cholesterol concentrations in men. Colonic short-chain fatty acids (SCFA) may affect hepatic lipid metabolism. Lactulose increases colonic acetate production, whereas L-rhamnose increases propionate. To test the effects of oral L-rhamnose and lactulose for 28 d on fasting concentrations and hepatic synthesis of lipids in humans, 18 men were administered 25 g/d of L-rhamnose, lactulose, or d-glucose for 4 wk in a partially randomized crossover design, with blood collected from fasting subjects on the first and last day of each period. Cholesterol and triacylglycerol (TG) synthesis rates were determined using deuterated water uptake rate over the last 24 h of each period. Postprandial blood lipids, and glucose and insulin were assessed in 11 subjects on d 28. Fasting serum cholesterol was unchanged; however, when expressed as a percentage change, TG were decreased, relative to baseline, by L-rhamnose (-10%) and lactulose (-10%), compared with D-glucose, which increased serum TG (+11%). Net TG-fatty acid (TGFA) synthesis on d 28 was lower with L-rhamnose and lactulose than with D-glucose. We conclude that these results do not support a primary role for propionate in the cholesterol-lowering effect of soluble fiber. However, both lactulose and L-rhamnose lowered serum TG (expressed as a percentage change) and TGFA synthesis, compared with d-glucose, which increased them. Although these data are consistent with inhibition of TGFA synthesis by SCFA, other aspects of the metabolism of these sugars cannot be ruled out as putative agents of their TG-lowering effects.

L-Rhamnose isomer
Rhamnose occurs in nature in its L-form as L-rhamnose which is unusual since most of naturally occurring sugars are in D-form.