There is no actual study that shows that diet causes or cures Crohns (or any I.B.D.) As yet, no-one knows what causes the illness.
There are some people with food allergies who are wrongly told they have an I.B.D. When they address those allergies, and recover, they may believe that food cures I.B.D.
There are people with confirmed I.B.D who also have food allergies (or intolerances.) When their diet is adjusted they definitely see an improvement in symptoms.
Then there are the majority of sufferers who have to adjust their diet due to mechanical issues arising from the illness such as ulceration, narrowing, inflammation, scar tissue etc. Insoluble fiber becomes the greatest challenge in these cases. Some other food types (lactose containing foods for example) can also become a problem due to mechanical issues involving lactase secretion. However these majority of people do not generally have any real food intolerances. They can however end up with nutrient deficiencies which need correcting, and which can improve their health but which do not cure the illness.
There are also some foods found to increase the inflammatory response in the intestines of some individuals, and they are also limited where an issue arises.
Then there is the differing severity of I.B.D to deal with....
No two people respond the same way to the same diet.
I am also a person who was on a vegetarian whole food diet - and a trainer! Crohns did not spare me because of my diet or my state of health. But I do not attribute that to a cause. There are people who live on McDonalds and survive to old age untarnished by ill health. There are people who in spite of doing everything they can to stay healthy, end up battling some awful disease.
We do know of many health conditions which are directly related to obesity, and to nutrient deficiencies. So far, I.B.D. has not been shown to be one of them.
Hope you find a balanced diet to help with your symptoms - good luck.