As Churchill might have once said...

...Most astute of you, Acerbic. 

And I do agree with you.

 I am fat.

But I can lose weight. 

You, on the other hand, cannot change your nature. 

I can shed pounds and become svelte in some months -

 You, my dear, are going to be a complete nutter

 for the rest of your tragic life 

and there is no diet nor amount of exercise
 to expunge that affliction.