I found this new free-text study that looks at processed foods. The paper looks at the various elements of processed foods, like advanced glycation end products (AGEs), that can contribute to a leaky gut.
The paper knocks high-fat diets but also points out potential problems with fructose. It focuses on two supplements, glutamine and curcumin, as having potential to improve the gut barrier. There is also some information about cooking temperatures in the paper as well.