September 18, 2018

How does an FMT donor’s diet affect the recipient?

Here is another question from one of my readers.

Q: Hi Michael,
Thanks for sharing your story and information.
I have been unsuccessful in finding clear information about how the food that an FMT donor eats might effect the recipient. I understand that gluten should be avoided with IBS but should the donor also avoid it during the transfer period? What about any allergies or foods that the recipient reacts to? Should the donor also avoid those? I don’t fully understand what the colon does with the stool so not sure how much of whats in the donors stool besides the bacteria gets retained or absorbed. Also what about alcohol such as wine and beer?
I was diagnosed with Crohn’s Colitis about 10 years ago that effects my large intestine. I do not take medication for it and have been treating it mostly with diet (Often SCD based) and now working with my MD who is a functional medicine practitioner. With his support I started doing home FMT’s on Dec 2nd 2013 and have done about a dozen transfers. I would like to continue but want to give my donor a little more leeway in her diet if possible.

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A: You’re welcome. As you note, there isn’t a lot of clear information and at this time no research to say how what an FMT donor eats could affect the recipient. I can say that my donor did not significantly alter his diet, although I limited my own diet when it came to foods which appeared to cause diarrhea or excessive gas, including unfermented dairy and insoluble fiber from nuts, fruits and vegetables and avoided carbonated drinks and caffeine. However sometimes these problems seemed to happen in spite of attempts to limit my diet. Over time I found that foods I used to consider problem foods no longer seemed to cause significant problems as my digestive symptoms continued to improve and presumably my colon was healing and my bacterial composition more closely resembled my donor’s and I was taking anti-depressant drugs that also appeared to help my digestion. So I think it is possible that some food intolerances and allergies may be eliminated by healing the gut and altering the gut bacteria.

However that is just my experience and my interpretation of it. However by weighing various personal experiences along with our best knowledge of how digestion works and what passes into stool we can come up with a somewhat more solid answer to this question.

According to what we know about digestion and alcohol metabolism it does not pass into stool. So moderate drinking that does not significantly affect the donor’s general health or digestive function should not cause any problems for you as the recipient. As for food, the vast majority of food is digested and most nutrients have already been absorbed by the time they reach the colon and it would not be present in stool. However there are some things that pass into the large intestine without being completely digested including insoluble fiber from seeds and fiber from fruits, vegetables and nuts and certain food molecules like complex carbohydrates pass into the large intestine without being digested. However many of these food molecules excluding some of the insoluble fiber may be broken down by the bacteria in the colon through fermentation. These bacteria from the donor would likely take root in the recipient, so that things should not be a problem.

Those like you who are on the Specific Carbohydrate Diet (SCD) or something similar like a gluten-free diet, or have significant food allergies either documented or suspected might worry about these problem foods being present in stool and whether the donor should also avoid those foods. If food molecules in the donor’s stool are undigested and have not been broken down by bacterial fermentation, then this could be a problem. However if these foods do not cause a problem in the donor in the form of excessive gas, constipation or diarrhea then it could be because the donor has the necessary enzymes to digest them or the bacterial flora to effectively break them down through bacterial fermentation. Alternatively it is possible the foods might be a problem to the recipient but are not to the donor because the donor has a healthier gut which is immune to potential problems that could be caused by these foods.

While I can not speak from the perspective of a trained dietitian or doctor, I don’t think the donor’s diet should be a problem for the recipient as long as it is not a problem for the donor. My donor did not follow the Specific Carbohydrate diet or other restrictive diets and ultimately things worked out for me and I have been symptom-free and have not taken any drugs specifically prescribed to treat Ulcerative Colitis since December 2011. However it should also be noted that my recovery was also aided by whey protein shake supplements to help repair damaged tissue, as well as anti-inflammatory drugs like mesalamine and immune suppressant drugs including Prednisone and also the anti-depressant drug Bupropion (which may inhibit some forms of immune response by inhibiting the activity of TNF-a to trigger inflammation.