# What Is '70% of Our Immune System' DOING in Our Digestive Track? **URL:** \ **Category:** Factual Questions\ **Created:** [June 15, 2016, 5:33am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402 "2016-06-15T05:33:36Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [June 15, 2016, 5:33am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/1 "2016-06-15T05:33:36Z")
There is this yogurt commercial, that shall remain nameless, that brings up an interesting fact. A full 70% of our immune system, is actually found in our digestive track. As I said, it shall remain nameless. So I don’t have a cite. But I assume it is an established medical fact. I mean, why would they want to deceive us (besides wanting to sell us their product, and all that)? My question is simple: What on earth is 70% of our immune system _ **doing** _, in our digestive track? Shouldn’t it be in our blood system and organs, protecting us from dangerous pathogens? And if it is mostly in our digestive track, it sure doesn’t seem to be doing its job. We have plenty of friendly bacteria there. It doesn’t target that. But still, outside bacteria is still outside bacteria, isn’t it? Also, I get mild cases of food poisoning all the time. So it certainly doesn’t seem to be helping me? What is it doing there? 🙂 ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [June 15, 2016, 6:05am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/2 "2016-06-15T06:05:28Z")
Sounds very scientific and factual, doesn’t it? Sounds like Marketing Bullshit, to use the technical name for such claims. My favorite, however is “I’m not a doctor, but I play one on TV”. Hey - same thing, right? I’m sure your knowledge of Medicine is as good as that of real doctors! “70% of your “immune system” lives in your gut” just doesn’t even come close “Same As A Real Doctor”. Come back when you have a real classic of **“Marketing Horseshit, Medical Topic”** to share. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [June 15, 2016, 8:08am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/3 "2016-06-15T08:08:30Z")
> [@Jim\_B](#): > > My question is simple: What on earth is 70% of our immune system _ **doing** _, in our digestive track? Shouldn’t it be in our blood system and organs, protecting us from dangerous pathogens? How do you suppose dangerous pathogens normally get into your blood system and organs? It’s of course not a medical fact, but the digestive system is one of the places in the body where very permeable parts of our exterior (remember your topology, if we ignore nose and ears the human body is a donut) is constantly exposed to pathogens. ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [June 15, 2016, 8:44am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/4 "2016-06-15T08:44:29Z")
A large part of our immune system is closely associated with our digestive sytem. Gut-associated lymphoid tissue ([GALT](https://en.wikipedia.org/wiki/Gut-associated_lymphoid_tissue)) is indeed a major part of our immune system. As part of the Mucosa-associated lymphoid tissue (MALT) it hosts lymphocytes, macrophages and other cells that participate in immune responses. Considering that our digestive system is laden with bacteria, it makes sense that it is under strict supervision by the immune system. [The Gastrointestinal Immune System](http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/gi_immune.html) ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [June 15, 2016, 12:14pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/5 "2016-06-15T12:14:13Z")
The problem with claims like this (which may be true in a quantitative sense) is that they imply that the product(s) being sold are going to boost one’s immune system, which is another kettle of (rancid) fish. “Gut health” is a big buzzphrase these days, and marketing is way ahead of the science. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [June 15, 2016, 12:22pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/6 "2016-06-15T12:22:50Z")
> [@Jim\_B](#): > > My question is simple: What on earth is 70% of our immune system _ **doing** _, in our digestive track? Shouldn’t it be in our blood system and organs, protecting us from dangerous pathogens? The digestive tract is where stuff from outside the body is brought inside the body. It’s important to regulate what gets in and what doesn’t. It doesn’t work perfectly, but it does work most of the time. ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [June 15, 2016, 12:38pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/7 "2016-06-15T12:38:12Z")
Your [gastrointestinal digestive tract](https://en.wikipedia.org/wiki/Human_gastrointestinal_tract)starts basically at the **mouth** and end at the **anus**. > [@](#): > > _The GI tract includes all structures between the mouth and the anus,[2] forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine._ That’s the most exposed part of your body to foreign intruders, even tho it’s internal, besides the skin and the lunges for breathing. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 15, 2016, 1:32pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/8 "2016-06-15T13:32:06Z")
One problem with taking antibiotics unnecessarily is that they kill off large numbers of beneficial bacteria in our guts. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [June 15, 2016, 1:43pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/9 "2016-06-15T13:43:46Z")
Most of the problem is deciding what measure to use to determine the “70%”. The acid in your stomach kills a lot of pathogens – does that make it a part of the immune system? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [June 15, 2016, 3:23pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/10 "2016-06-15T15:23:33Z")
It’s a statement that can be found in the medical literature. And then misapplied to make it more general than it actually is. The most relevant article is [Allergy and the gastrointestinal system](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515351/) from Clin Exp Immunol. 2008 Sep; 153(Suppl 1): 3–6. > [@](#): > > 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. When you read the full article, however, you soon realize that it refers specifically to food-based allergic reactions. That is not the “immune system” as most people generally understand the term, which is generally taught as the white blood cells. > [@](#): > > The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. One of the important cells involved are white blood cells, also called leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substances. It shouldn’t be surprising that the gut plays a part in defending against food-based allergens. That article explains the mechanisms - as far as they are known, which isn’t all that far - and the possible consequences. The danger comes from taking a specialized medical finding and applying it to areas where it doesn’t belong. This claim is technically true, which I define as a fact so wrenched out of context that it appears to mean the opposite of what it does. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [June 15, 2016, 4:42pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/11 "2016-06-15T16:42:13Z")
> [@Broomstick](#): > > The digestive tract is where stuff from outside the body is brought inside the body. On the other hand, the digestive _track_ is the route you take through the duodenum, making a hard left at the sphincter of Oddi in order to get to the pancreas before it closes for the night. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [June 15, 2016, 4:45pm UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/12 "2016-06-15T16:45:04Z")
> [@Jackmannii](#): > > On the other hand, the digestive _track_ is the route you take through the duodenum, making a hard left at the sphincter of Oddi in order to get to the pancreas before it closes for the night. Does that make the yogurt commercial the real digestive [tract](https://en.wikipedia.org/wiki/Tract_(literature))? ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [June 16, 2016, 9:55am UTC](https://boards.straightdope.com/t/what-is-70-of-our-immune-system-doing-in-our-digestive-track/757402/13 "2016-06-16T09:55:48Z")
> [@leahcim](#): > > Most of the problem is deciding what measure to use to determine the “70%”. The acid in your stomach kills a lot of pathogens – does that make it a part of the immune system? The prime function of the stomach acid [(Gastric Acid)](https://en.wikipedia.org/wiki/Gastric_acid) is to digest your food, but it also helps to inhibits microorganisms from growing due to the acid environment. > [@](#): > > _The highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein’s peptide bonds. The gastric chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen, and in infancy rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection._