I recently read an article where butyrate production was maxed out at around 15g of fiber, but I can't find it anymore, and it may not have been telling the whole story. So my faithful minions, bring to me some research that answers my question...so that we may take over the world! Mwahahahaha.
asked byStabby (17969)
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on January 10, 2012
at 11:25 PM
This page: Physiological Effects of Dietary Fibre provides an interesting overview of the process, and gives a relevant table regarding the usability of various types of fiber. However, no elaboration is provided on the extremely inaccurate range given for cellulose, the primary fiber we ingest from vegetable sources.
Dietary Fibre | Fermentability (%)
- Cellulose 20-80%
- Hemicelluloses 60-90%
- Pectins 100%
- Guar gum 100%
- Ispaghula 55%
- Wheat bran 50%
- Resistant starch 100%
- Inulin, oligosaccharides 100% (if they are not in excess)
And this study: Short chain fatty acid absorption by the human large intestine states:
We have demonstrated absorption rates for short chain fatty acids of between 7-7 and 8-9 /Lmol/cm2/h in the human rectum which are similar to those observed in animal studies-for example, 10-5 ,umol/ cm2/h for rumen epithelium (Stevens and Stettler, 1966); 8'6 for equine large intestine (Argenzio et al., 1974), and 9 4 in the large gut of the pig (Argenzio et al., 1975).
So from those two sources we can glean that we are capable of fermenting fiber into SCFAs in the intestines, and we are capable of absorbing said SCFAs (see pg 3645 on this study for amounts of each SCFA produced during the fermentation of various types of fiber - note that butyrate is actually the least common), albeit at an slightly inhibited rate in comparison to species designed to live on the process.
The above study concludes by giving us an educated guess, more or less (perhaps this is where you got the 15g number?):
Although we have not measured the total capacity of the large bowel to absorb short chain fatty acids, this may be deduced by other means. On a typical daily intake of 20 g of fibre in Britain, 10-15 g are broken down (Southgate and Durnin, 1970). This would result in the production of at least 100 mmol of short chain fatty acids. No figures are available for the production of short chain fatty acids from other dietarysources but a total of 5-20 mmol of short chain fatty acids are known to be excreted daily in the faeces (Cummings et al., 1976). Thus at least 80 mmol are unaccounted for which could be further metabolised by bacteria or absorbed and would then yield 100 kJ. In parts of the world where fibre intakes are much higher, in the range 60-175 g daily, equivalent processes could yield appreciable quantities of metabolisable energy.
Based on that, I would venture a guess that we are limited by our amount and type of gut flora, the fermentability of said fiber source, and possibly other factors, moreso than the sheer volume of fiber consumed. This study: Regulation of short-chain fatty acid production would agree:
In addition to the importance of gut transit time, mentioned earlier, many host-related factors affect bacterial metabolism and SCFA formation in the gut, including diet and other less direct determinants such as ageing, neuroendocrine system activity, stress, pancreatic and other secretions in the digestive tract, mucus production, disease, drugs, antibiotics and epithelial cell turnover times. From a microbiological viewpoint, the chemical composition, physical form and amount of substrate available affects bacterial fermentation reactions, which are also dependent on the types and numbers of different bacterial populations in the gut, catabolite regulatory mechanisms, the availability of inorganic electron donors, such as nitrate (Allison & Macfarlane, 1988) and sulfate (Gibson et al. 1993), as well as competitive and cooperative interactions between different species in the microbiota (Macfarlane & Gibson, 1994).
on January 10, 2012
at 11:31 PM
I don't believe there's a definitive answer to this for humans across the board. Different intestinal flora convert the fiber to differing amounts of Butyrate. Different fiber types convert to differing amounts of Butyrate. Intestinal PH values affect conversion. Rat studies don't apply to humans, etc. This paper probably has more info than you'd want to know, and is pretty thick reading.
That said, I didn't see anything about a maximum in it, unless it was related to human trials and dosing they used. I was looking for something where they had 3+ sets of dosing (and little change after a certain point) but didn't see anything close.
What I think you're looking for is "What is the optimal amount I should eat per day", and I don't think there's a firm number for that. It's got too many variables. Plus, if everything is the same, the intestinal flora will grow off the nutrients you give it, and can process more tomorrow than it can today (up to a point).
on November 05, 2013
at 09:54 PM
Gorillas have just one stomach, and yet they manage. So
pectin -> pears, apples
resistant starches -> potatoes, other roots
inulin -> varying amounts in roots
and we are talking of order 100 cal/ day. These SCF have also anti-inflammatory properties as per the Whole Health Source blog. What's not to like?
on November 13, 2012
at 11:50 AM
Try secondary hind digestion;like a rabit. Bacteria does the job after the stomach starts it.
on January 07, 2012
at 05:12 AM
Think that the number might be somewhat higher, but don't know for sure.