A recent commercial for a particular brand of yogurt claims, among other things, that 70% of your immune system is located in your gut. I have seen this claim repeated here (the emphasis is mine):

The Intestine/Immune Connection:

Most people don’t know that 60-70% of their immune system is located in the gut as a vast network of lymph tissue referred to as GALT (gut associated lymphatic tissue).

And repeated without explanation in a few other places, e.g.:

All of these sources appear to be pushing some form of edible immune boosting product, and they use the 70% claim in a strange form of logical deduction that says "70% of your immune system is in your gut; our food goes into your gut; thus, our food is good for your immune system."

I'm not interested in how and/or whether these products work, as there are other skeptics questions dealing with that claim. I'm just asking about the "70%" claim. In particular, I would have guessed that most of the cells that make up our immune system would be located in our lymph nodes, blood stream, and bone marrow.

Before anyone asks, I have no idea what they are measuring 70% of, so I'm not even sure that the claim makes sense as written. If someone can explain what measurement makes the 70% figure true, that would be a very helpful answer. Otherwise, I'm mostly interested in actual medial science that could explain how the immune system is "distributed" through the body and how much of that can be attributed to the digestive system.

  • 1
    One thing is where the immunity is located, I don't think that this is something to be so sceptical about. The "skeptics" part here is: "and whence you need our super sexy cool yoghurt which is actually not a yoghurt at all".
    – yo'
    Commented Sep 15, 2016 at 11:39
  • So the answer is yes due to Probiotics helps the digestive systems. Commented Aug 21, 2020 at 14:02

2 Answers 2


Possibly yes, depending on your definition of "your immune system": I suspect that something like the following is their justification for the claim.

Functional food science and gastrointestinal physiology and function includes,

3. The gastrointestinal immune system

3. I. Gut-associated lymphoid tissue (GALT)

(Brandtzaeg et al. 1989)
The first, and in normal individuals only, contact that ingested bacteria, including probiotics, have with the immune system is with the GALT. The human intestine represents the largest mass of lymphoid tissue in the body, containing over 10^6 lymphocytes/g tissue. In addition, about 60% of the total immunoglobulin (Ig; several grams) produced daily is secreted into the gastrointestinal tract.


A 2008 article published in the Journal of Clinical and Experimental Immunology states, "The crucial position of the gastrointestinal system is testified by the huge amount of immune cells that reside within it. Indeed, gut-associated lymphoid tissue (GALT) is the prominent part of mucosal-associated lymphoid tissue (MALT) and represents almost 70% of the entire immune system; moreover, about 80% of plasma cells [mainly immunoglobulin A (IgA)-bearing cells] reside in GALT." (Src: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515351/)

So to answer your question about what they are counting it would appear to be a percentage of the total immune cells in the body.

Unfortunately, this is from the ABSTRACT portion of the paper and they do not provide further references to their sources.

A 2009 article found in 'Seminars in Immunology' opens with the following statement, "IgA is the most abundant immunoglobulin isotype produced in the body (around 3 g/day) and it is estimated that around 80% of all IgA-antibody-secreting cells (ASCs) reside in the gut mucosa [1,2]." (Src: http://vonandrian.hms.harvard.edu/Publications/2009/Mora_2009.pdf)

Unfortunately, when I try to follow their references both articles require access permissions that I do not have, but maybe you have more permissions than I do and call pull them up, they are as follows:

[1] Suzuki K, Ha SA, Tsuji M, Fagarasan S. Intestinal IgA synthesis: a primitive form of adaptive immunity that regulates microbial communities in the gut. Semin Immunol 2007;19(2):127–35. http://www.ncbi.nlm.nih.gov/pubmed/17161619

[2] Macpherson AJ, Slack E. The functional interactions of commensal bacteria with intestinal secretory IgA. Curr Opin Gastroenterol 2007;23(6):673–8. http://www.ncbi.nlm.nih.gov/pubmed/17906446

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