Can avoiding certain foods reduce inflammation? (Gluten, sugar...)

Question

Lots of articles and books claim from moderate (help reduce inflammation) to miraculous (cure or completely eliminate symptoms of autoimmune disorders) claims about doing strict diets that avoid specific types of food. Some of them also claim things like inflammation-causing foods being the spark that trigger chronic inflammatory medical conditions such us Hashimoto disease or progressive multiple sclerosis, (see e.g. The Wahls Protocol or The Top 13 Causes of Inflammation: And How to Treat It Naturally, but there are countless others). One of the most repeated statements is that they create a "leaky gut", described as:

Leaky gut, or intestinal hyperpermeability, is a phenomenon that occurs when the tight junctions of the intestinal wall become loose, allowing harmful substances to enter the bloodstream.

Gluten is probably the most commonly and intensely demonized for causing leaky gut, but also sugar and certain pesticides. Note that in the same Healthline article linked above it is stated that

Leaky gut syndrome remains a bit of a medical mystery, and medical professionals are still trying to determine exactly what causes it.

Also, often these articles or videos throw in some foods increasing or nourishing some bad bacteria in the microbiome into the causes.

I have two questions:

• Is there any evidence that certain foods like gluten trigger inflammation in humans?
• Is there any medical study done on patients with inflammatory and autoimmune conditions that shows that patients can improve their symptoms by avoiding certain pro-inflammatory foods?

Answer 1

There are actually two possible answers here. One is simply answering the title and a different answer regards the content of the question.

That restricting certain types of food can reduce bowel inflammation has been proven by the Low-FODMAP diet, if you make a research for scientific papers on the diet you can find plenty of evidence. So the answer to the title is yes.

Then in the text of the question you link the hypothesis to other methods and you explicitly link it to gluten. But you also ask about nourishing bad bacteria in the microbiome. Here there are many different answers.

For example, that some sweeteners could nourish bad bacteria is currently being studied, but the field is vast and this kind of research does not have a lot of support, so final evidence is very far. Also the opposite, the possibility to nourish good bacteria is a still ongoing research, but the marketing from probiotic firms makes it difficult to understand.

Also the restriction on gluten does not have a definitive answer because it would imply another question like what do you replace gluten with? Food labelled as gluten free includes a wide range of ingredients and there is no evidence that all of them are harmless. For example buckwheat is often used. Researches linked to the Low-FODMAP diet gave some positive evidence, but there is no definitive evidence given the number of possible variations.

For what matters the Wahl protocol, the Low-FODMAP diet already gave some evidence that certain restrictions give some relief, but there is no evidence that the new protocol is actually an improvement over the existing guidelines.

You can consider this a partial answer because I will skip the autoimmune diseases.