Konjac mannan and vitamin absorption in people
What it found
In a small study in people, konjac mannan reduced the absorption of vitamin E but not vitamin B12.
The authors suggest it may affect fat-soluble vitamins by removing bile acids.
What they found
Studies in people
Vitamin E absorption
In both normal and diabetic subjects, the absorption rate of vitamin E was reduced when konjac mannan was added to the test meal.
Vitamin B12 absorption
Konjac mannan did not reduce the absorption of vitamin B12 in normal or diabetic subjects.
Bile acid removal
The authors suggest that konjac mannan reduces fat-soluble vitamin absorption by removing bile acids, but does not reduce fat-insoluble vitamin absorption.
Diabetic vs normal
The absorption rate of vitamin B12 in diabetic subjects was much higher than in normal subjects. The reason for this is not clear.
What the authors conclude
“In this study, we showed that konjac mannan markedly reduces vitamin E absorption as assessed by the vitamin E tolerance test, removing bile acids.”
Also in their conclusions
- They conclude that konjac mannan markedly reduces vitamin E absorption by removing bile acids.
- They advise that care should be taken in the use of these dietary fibers for diet treatment.
How it was done
High-fiber diets may help diabetics by lowering blood sugar and blood fats, but how they work is not clear. The authors wanted to test whether konjac mannan binds bile acids in the body by looking at its effect on vitamin B12 and vitamin E absorption.
Six healthy volunteers aged 20 to 61 and five maturity-onset diabetic patients aged 57 to 81 were given a test meal with vitamin B12 and vitamin E, then a second meal with 3.9 g konjac mannan. Blood samples were taken before the meal and after 1, 3, 5, 8, 12 and 24 hours.
What it can’t tell you
- This was a small study with only 11 people, so the results may not apply to everyone.
- The study did not test whether these changes in vitamin absorption affect health over time.
The paper
- Title
- Influence of dietary fiber (konjac mannan) on absorption of vitamin B12 and vitamin E
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Doi K, Matsuura M, Kawara A, Tanaka T, Baba S (1983). Influence of dietary fiber (konjac mannan) on absorption of vitamin B12 and vitamin E. The Tohoku journal of experimental medicine. doi:10.1620/tjem.141.suppl_677Free full textPubMed 6096987DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error