Simplest and fast food is whole wheat toasts with all-peanut butter and some variety of greens (bell peppers and lettuce work for me) -- and I take a few varieties of seasonal fruits. Usually I fry two large onions in a large frying pan and canned beans and/or peas good for two large meals. Of course seeds and nuts with a few cookies/pies/cakes!

The Mediterranean-DASH Diet Intervention for Neurodegenerative Delay, or MIND diet, targets the health of the aging brain. This is what Harvard Health says which I suppose isn't different than what Mayo would.
Counting calories methinks is a sure way to hate food -- something that needs to be Enjoyed not used as a medicine with trepidation. Our bodies developed its signals to tell us when we are no longer hungry. Let's keep that instinct intact.

For your IBS, I'd talk to my doc, tho most veggies can be light steamed (I do often the hard ones collard/kale) Good luck!
https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/mind-diet/