Do this, scientists! (experiment to confirm/deny the existence of "leaky gut")

[HayInNeedleStack 1]

Leaky gut is a condition that we have little knowledge of. 

The symptoms this condition could cause are not agreed upon. Some health practitioners say it could cause "wide range of long term conditions [1], like chronic fatigue syndrome and Multiple Sclerosis.

The possible cause list NHS gives is much more accurate:

• inflammatory bowel diseases – such as Crohn's disease
• infections of the intestines – such as salmonella, norovirus andgiardiasis 
• coeliac disease 
• chemotherapy medicines
• chronic kidney disease  
• radiotherapy to the abdomen (tummy)
• immunosuppressants (medicines that weaken the immune system)
• HIV/AIDS 
• cystic fibrosis  
• type 1 diabetes
• sepsis
• complicated surgery

As you can see, the list includes a lot gastrointestinal conditions. Gut becomes "leaky", letting too big particles into blood system, and possibly these particles act as poison (because they are not  supposed to be in the blood, thus the possible bad effects).

Now, to confirm this disease, I was amazed that this test hadn't been done before:
Feed the supposed "leaky gut" patients (e.g. celiacs with damaged bowel) with IV fluids. Because these fluids go directly into the blood stream, and the particles are "elemental" (glucose, vitamins, amino acids... all supposed to be in the blood stream anyway), they shouldn't cause any symptoms.

If they notice improvement, the problem is in the digestive system (I'm also including stomach). If not, such condition as "leaky gut" doesn't exist. Rather the problem is how the body reacts to the "elemental" particles. E.g the most common explanation would be diabetes (the IV fluids just caused elevated glucose levels), that also should be tested. Also the "candida theory", because its proponents say the candida is in the WHOLE body, including the blood stream. To eliminate this, patients should take anticandida meds, then again go on IV fluids, and if they NOW get better, it was candida. If not candida, and not diabetes, nor allergies, we have a new condition we aren't even aware of (body reacting to elementary particles with no obvious reason).

However, if the patients DO get better, the problem IS in the gut. Now, it could be celiac disease, and the improvement could have been due to eliminating gluten from the diet (because IV doesn't contain gluten). The question remains that did the bowel actually leak any particles? (not just gluten causing autoimmune reactions and malnutrition, and explaining all the  300 symptoms).  Or the patients just get better due to NOW acquiring all the necessary nutrients.  To eliminate these possibilities, they should feed the patients with gluten-free food (or even better, with elemental diet, because it could also be lack of digestive enzymes or something else). If they get worse, the problem is STILL in the gut, and thus the "leaky gut" exists. If not, "leaky gut" is probably a non-existent condition.

[stri8ed 9]

Leaky Gut aka intestinal hyperpermeability, is very much a real condition, and there are existing scientifically credible tests to measure the degree of permeability. (see lactulose-mannitol test). Now whether or not various conditions are caused by this, is an entirely different question.

While an IV based elemental diet might help identify the GI as the culprit, it's both costly and not sustainable. So I fail to see what is gained. You can just as well do a water fast, and reach the same conclusions.

[HayInNeedleStack 1]

Good idea! Add also the lactulose - mannitol test, to confirm they are/are not experiencing leakyness in the gut, then correlate the results with the symptoms (obviously digestive symptoms would have to be excluded, because diarrhea and bloating will probably be present anyway, due to having damaged intestines).

You see, ironically it would be "gluten-free challenge", because possibly systemic symptoms ("leaky gut syndrome")  and GI symptoms start after going IV fluids -> gluten-free (instead of "gluten challenge", which would be gluten-free -> gluten).