I think you need to know the individual to understand their tolerance levels of certain nutritions.
You may have one person who eats burgers all day, drinks coke, smokes and is still somehow healthy, thin and fit. Whilst on the other hand another person practising a healthy lifestyle to get the life kick out of them if they even look at chocolate
It is also physiological as well, the mind is a powerful tool and somewhat determines what foods we are "OK" with and what foods we "aren't OK" with.
Again this comes down to the person's metabolic rate (metabolism).
Another is inheritance - you may inherit a gene that tells your body "right, we like storing fat, so any fat we get we store" whilst someone else's genes may simply say "we will try and burn fat at the chance we get" - metabolism.
Which comes to the conclusion it completely depends on the person. Know your own limits but be sensible about it. The more you try and follow "guidelines" the more robotic you become. Know your own body (I'm not saying eat burgers all your life but you get what I mean, if you're better with certain types of foods than others, eat it).
Moderation is key. You can still have a treat once in a while your body
can deal with it. If people stop starving themselves and eating very little to try and fit into the "healthy" lifestyle they'll soon find out that essentially your body is putting itself into "starving" mode and storing everything, which makes sugar and fat look really bad because as soon as you eat it you get a rush which your body cannot handle.
So fat and sugar now and again is
needed for a healthy lifestyle, your body needs to know what it is and how to handle it from time to time so you don't overload yourself when you
do have it.
Besides, I say to simply enjoy life and tasty food!!!!