This is not a professional opinion but...
I eat a 'fit for life' diet. It is not just what I eat but when. I only eat fruits, fresh fruit juices, water, coffee and meds in the mornings til noon. Then at noon it is usually a protein and a vegetable (work days it is Greek yogurt and cherry tomatoes and radishes for simplicity sake). At home, it can be grilled meats or chicken and a salad and artichoke.
Ditto for dinner or a bowl of pasta with no proteins.
Last Thursday...I decided to go on a massive croissant binge on the way to work. I hit 3 different bakeries to try their croissants...1 from each (I threw out the worst one). Within 1/2hr of eating them my knees hurt, my body felt 'heavy' and slow and I was sleepy, crampy, cranky, achy, gassy, bubbly, bloaty (all 7 dwarfs).
I hadn't done that in years...So although not a scientific study, I got my answer.
FIt for life has worked for me since 1991. It gave me back the control of my life and my pouch, reduce my pouchitis and saved me years of misery.
But that is me...not necessarily for everyone
Sharon