Eat Better, Eat Together Month on October, 2019: My cat have not ate in months!!?
October, 2019 is Eat Better, Eat Together Month 2019. October is National Eat Better, Eat Together Month! - Meal ... Finding time just to eat
If the cat is eating canned food, almost any kind, he is better off than he would be eating the dry prescription food.
Wet food is much better for cats that dry because it keeps them appropriately hydrated and lessens the chances of urinary tract blockages.
Fancy Feast isn't the best food but it isn't the worst either.
I suggest that you feed him as much as he wants of the Fancy Feast, choosing the varieties that do not contain any fish. Additionally, add a small amount of water to each meal. Don't add so much that it will make it unappetizing. Try three meals a day with a teaspoon of water mixed into each.
At 18 years of age it is much more important that he eat than rather what he eat. If your 18 year old cat wants Fancy Feast, that is what you are better off giving him.
Here is some information on the issues with dry cat food and urinary tract issues. It is a bit of a read but do read it:
Should i just stop eating all together?
Don't stop eating all together, you'll develop an eating disorder and that wont do much good. If you really want to lose weight, do it a healthy and natural way like giving up junk food or soda drinks. Also you could join a local gym and do more exercise or join a group like 'weight watchers'.
I wish you all the luck in the world because I know what it's like to be the 'fat one'. But DON'T stop eating all together because that just leads to anorexic, believe me, I know.
*When you eat carbohydrates your body releases insulin and that helps fat get stored. This is the way to eat in order to lose weight.*
Now it is better to have 2-3 days mixed meals, 2 days carbohydrates meals (whole pasta/rice/skin on potatoes) and two days fat meals (meat/fish/dairy). I trust you eat no sugars. Eat until you feel full and if you see weight coming back stop eating together fat and carbohydrates.