Konjac mannan and absorption of vitamins B12 and E in people
What it found
Adding 3.9 g of konjac mannan to a meal lowered how much vitamin E was taken in by the gut in 11 people.
It did not change how much vitamin B12 was taken in.
What they found
Studies in people
Vitamin E absorption dropped
When 3.9 g of konjac mannan was added to the meal, less vitamin E entered the blood in both healthy people and those with diabetes. The authors think the fiber removed bile acids that the body needs to take in vitamin E.
Vitamin B12 stayed the same
Adding konjac mannan to the meal did not change how much vitamin B12 was taken in by the gut. This was true for both healthy adults and those with diabetes.
Higher B12 uptake in diabetics
People with diabetes took in much more vitamin B12 than the healthy group. The authors say they do not know why, though the two groups differed in age and blood sugar levels.
What the authors conclude
- They conclude that konjac mannan lowers the amount of vitamin E the gut takes in by removing bile acids, but it does not affect vitamin B12.
- The authors advise that care should be taken when using these dietary fibers as part of a diet plan.
How it was done
High-fiber diets can lower blood sugar and cholesterol, but scientists wanted to know if konjac mannan also blocks bile acids needed to take in certain vitamins. They tested this by measuring how well people absorbed vitamin B12 and vitamin E with and without the fiber.
Six healthy adults aged 20 to 61 and five older adults with diabetes aged 57 to 81 took part. On one day they ate a test meal with added vitamins, and on another day they ate the same meal plus 3.9 g of konjac mannan. Blood samples were taken before the meal and at 1, 3, 5, 8, 12 and 24 hours after.
What it can’t tell you
- Only 11 people took part, so the results might differ in a larger group.
- The study measured what happened over 24 hours after a single dose, so it cannot show what happens when someone eats konjac mannan every day for months or years.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error