How do longer Fasts affect Gut Bacteria?

by 22684 · September 01, 2013 at 02:58 PM

Trying to find studies on longer fasts 3+ days and how it relates to gut bacteria. Anyone help me find some science?

Specifically bad bacteria die-off, preservation of good bacteria, etc.

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6 Replies

135 · March 19, 2011 at 02:30 PM

After a longer term fast, my initial foods are solely fermented ones for the next day or two.

3142 · March 19, 2011 at 02:36 PM

Not exactly what you are looking for, but somewhat pertinent: http://www.ncbi.nlm.nih.gov/pubmed/19700553.

And I agree with Bill, that some of the population 'might' die off. You won't be eating any soluble fiber for them to chow down on. Though bacteria are resourceful little beings that I'm sure could survive for a good amount of time (while you fast) without dying (Source: Microbiology course*). From an adaption standpoint of early human beings, it wouldn't seem right for a good amount of the beneficial gut flora to die during an extended period without food ... would it? Just speculation from me though.

*if you'd like me to find the book title just let me know and I'll try to find it

20 · March 12, 2013 at 09:33 AM


the 'fasting' mentioned in the study was merely a reduced calorie diet consisting of fruit juice and vegetable soup. This would be very unlikely to significantly change the gut flora over an eight day period.

However from personal experience a 10 day extended fast (non-nutritive fluids and vitamins only) almost completely stops feces production. This indicates that bacteria numbers are massively reduced.

10750 · April 04, 2011 at 12:57 AM

This old study might apply http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1552988/pdf/gut00700-0056.pdf

I think your best study is this:

Mediterranean diet or extended fasting's influence on changing the intestinal microflora, immunoglobulin A secretion and clinical outcome in patients with rheumatoid arthritis and fibromyalgia: an observational study http://www.biomedcentral.com/content/pdf/1472-6882-5-22.pdf

Keep in mind that...

If you look up 'bacterial sporulation' you will find that many bacteria, when they have run out of food, will 'select' a few of their numbers to undergo sporulation (colony sporulation factor), and these spores are very stable over time and in varying acidities, 'waiting' for the right conditions to come back. Sporulation is used by some probiotics as a way to make sure that the desired strains make it through the stomach acid so that they might better colonize the intestines.

as RG73 points out, only some bacteria do this, but there are many ways for bacteria to survive for extended periods. DIG INTO http://en.wikipedia.org/wiki/Gut_flora for more details on huge variety.

The Arthur Andrew site says it pretty well while promoting their high-end probiotic Syntol:

Spore germination is a dependable means of delivering healthy flora to the intestine in less than ideal conditions. Most bacteria are susceptible to any acidic pH range, mainly thriving in the more alkaline lower GI, but spores are able to withstand a broader range of variables in regards to pH and temperature ranges. This improves the chances that the probiotic strain will properly germinate and begin the process of restoring intestinal balance.

0 · September 01, 2013 at 02:58 PM

NEW research coming up with two different interesting factors:

First, a 2009 to set the stage-- http://aem.asm.org/content/75/20/6451.full#content-block discusses the impact of fasting (on hamsters) on proportions of gut-bacteria. Of interest is the fact that Akkermansia muciniphila survives fasting at a proportionally higher rate than other bacteria.

Second, the new stuff-- http://www.pnas.org/content/early/2013/05/08/1219451110 suggests that that same bacterial strain has a tendency to be present in greater concentrations in people who are not overweight.

Questions I have that were not clarified in the first article is what is considered to be a "fast." Hamsters are not people; their metabolisms are capable of going through hibernation, but unlike humins, they don't have a huge amount of body-mass to burn through. So the translation, if any, to humin feeding patterns is unclear. I do not know if there was follow-up to that question in a future study.

In Jared Diamond's latest book, "The World Before Yesterday," he makes the observation that wild / traditional humin beings did not tend to have frequent, small meals--they were often forced to fast every few days, when hunting or harvesting fell short. Other information I've read talks about the impact of antibiotics on increasing the bacteria that facilitate carbohydrate digestion in feedlot animals. My conclusion--sorry, the two articles I offered are all I have the umph to collect!--is that the near-continuous exposure to antibiotics that I experienced as a child are likely related to a die-off of those bacteria most likely to maintain a lean body, and also that a weekly fasting day may be beneficial in encouraging an increase in the gut-bacteria which are more common in those humins without excess body fat.

2528 · February 18, 2011 at 04:13 PM

I have read that they pretty much stay the same, you might have a little bit of die off in population but the specific species and their proportions generally stay the same and will feed off the glucose you create from your own protein.

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