Those ppl probably regularly consume sugar and processed foods. On top of all that, of course any extra calories will be detrimental to them.
So they eat white only.

Eggs are very healthy, egg yolks have the best kind of fatty acid.
When I was deciding to become a vegan or vegetarian, being vegetarian was made so much easier cos how nutritional eggs are.

Nowadays a lot of health apps can track macro and micro nutrients.
I use Samsung Health, already come with the phone.

Can. In fact, if you eat just white, it's like an "empty food".

Food market, specifically sugar industry is like that. They say fat is bad. Fat is never bad.
In fact, if you already have cholesterol problem, you need more fat to produce hormones to reduce your cholesterol level.