I have a sliding scale of eating, not a diet.
I do not believe that diets help most people but only help them to maintain short term goals and then they go back to whatever was happening before the diet but only worse...
So I believe that you should slowly but surely substitute foods.
I traded white breads, cake and pastry for only whole grains. Then I waited a month until the next substitution once I was comfortable with it and it felt natural.
No margarine or white fats (lard, Crisco...) but olive oil or butter only...if I am going to get the fat I want the health benefit with it too.
Again I waited until it became second nature.
Gave up salad dressings and sauce and used balsamic vinegar or lemon with a few tsps of olive or walnut oil or any other natural oil. Mix some mustard into it and it makes a great creamy sauce. You can add tons of spices and herbs for different flavors.
I eat mostly grilled fish or chicken but enjoy red meat or lamb as a treat...I do not count calories, ever, but enjoy my food when I am eating it, drink lots of water Before the meal to fight off dehydration and fill my gut a bit and to not confuse hunger with thirst.
I have found that certain veggies work very well for me steamed, like broccoli, artichokes, asparagus (the top 2 inches only or the fibre is too much for me) and a few other so I start each meal with those and a green salad without too much stuff in it.
I clean out my system and pouch every day by only drinking liquids in the mornings (coffee, juice and water) until noon but I have a k pouch and it works great but not sure how it will work for a j pouch.
With just those steps I took off and maintained a comfortable lifestyle and body shape.
I eat too much ice cream ( sugar is my enemy and I am addicted) and other sweets so those are my weak points but even with all of that I have managed to keep to a reasonable weight (size 10) for most of my life.
I walk and move a lot unless I am in a flare (sacroilitis) and then all bets are off...I become a sad couch potato living off of sugar and the weight blooms!
By the way, Greek yogurt is my friend and I eat a lot of it for snacks and meal substitution whenever I am feeling peckish. Plain or light only...watch the sides of the containers for calorie counts, they can really get up there in some of them.
Sharon