Is the Autoimmune Protocol Diet legit and/or necessary? Is 'leaky gut' an actual thing?

I really can't tell, it's like everyone says something different. So many doctors online claim that eating certain foods (gluten, grains, soy, sugar, and even dairy/cheese or more usually) is what causes and exacerbates autoimmune diseases and that on top of taking your medication, removing those foods is necessary to ease your symptoms or heal at all.

So, how real is 'leaky gut' in general? Are dietary restrictions even necessary?