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Do viscous polysaccharides slow absorption by inhibiting diffusion or convection?
C A Edwards1, I T Johnson, N W Read
1Clinical Research Unit, Royal Hallamshire Hospital, Sheffield, UK.
European Journal of Clinical Nutrition
|April 1, 1988
Summary
Guar gum, a viscous polysaccharide, likely reduces nutrient absorption by hindering the mixing of intestinal contents. It slows down solute diffusion and counteracts the effects of intestinal contractions on absorption.
Area of Science:
- Gastroenterology
- Food Science
- Biophysics
Background:
- Viscous polysaccharides like guar gum are known to delay nutrient absorption.
- This delay is hypothesized to occur by limiting the access of luminal contents to the intestinal lining.
Purpose of the Study:
- To investigate the mechanism by which guar gum affects nutrient absorption.
- Specifically, to determine if guar gum delays solute diffusion or inhibits convection of luminal contents.
Main Methods:
- Electrical resistivity measurements were used to assess ion mobility and mixing times in saline solutions with varying guar gum concentrations (0.5-1% w/v).
- An in vitro model simulating intestinal contractions was employed, using dialysis tubing to measure glucose movement with and without guar gum.
Main Results:
- Guar gum did not affect ion mobility in unstirred solutions.
- Guar gum significantly increased the time required for mixing of saline solutions, directly correlating with increased viscosity.
- In the simulated intestinal model, guar gum inhibited the increased glucose uptake typically caused by simulated intestinal contractions.
Conclusions:
- Guar gum's effect on absorption is likely due to its ability to resist the convective forces generated by intestinal contractions.
- This resistance to convection, rather than a direct effect on diffusion, appears to be the primary mechanism for delayed absorption.