I changed my diet rather drastically about 8 months ago. I do high-fat, moderately low carbohydrate. It's working for me. The biggest difference, for me, is I no longer eat wheat, nor any other grains with the exception of occasional rice. The "wheat-ectomy" has made a positive difference in my health.
However, even doing the things I am (which I think are prudent), I realize that there is not one diet to suit everyone. We are all unique, not robot clones.
I believe any good diet becomes a lifestyle. Just getting rid of processed foods, and instead making everything from scratch is quite an undertaking, but will certainly make a huge difference to anyone's mental and physical health.
To eat too much of one food is a recipe for disaster. We need balance.