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I don't think its necessarily just sugar, its carbs also. I think people have had good success on a no carb diet. But I don't think a low carb diet is sustainable for most people which makes it a challenge.
Regarding dietary intervention. The most effective dietary intervention has so far been elemental diets, they can often drastically lower intestinal inflammation in patients.
There are lots of theories behind the mechanism of action of the diet. Yet the main difference between a regular diet and an elemental diet is its bioavailability. Elemental diets contain sugars (maltodextrins) that can easily be taken up high in the GI tract before reaching the small intestine. (maltodextrins are sometimes classified as complex carbs in some countries, in Europe they are sometimes reclassified as glucose syrup, but they are really sugars, depending on the level of hydrolysis, they are very close to pure glucose). Fats in elemental diets are in the form of MCT that are highly bioavailable.
Even though there was a study that linked the use of maltodextrin to the rapid proliferation of AIEC in a petri dish, this is not what we see in vivo. People on EN show a rapid decrease in bacterial load, including E Coli, maltodextrin can be taken up much higher in the GI tract, depriving bacteria in the small intestine and colon of nutrients.
The only problem I see with long term use of EN or diets that deprive bacteria of nutrients, is that one also diminishes bacterial diversity, there is not only a decrease of bacterial load with patients on EN, but it also involves a form of dysbiosis. The reintroduction of food might give AIEC a fitness advantage.