Gaining

I've heard many people saying that coke is really
really fattening I but checked on some fitness websites and a liter of coke is just like 420 cals. Is there any other factor contributing to weight gain

My coke nock off is listed as having 160 cal.per 12 oz serving, and about 6 servings per 2L. So that would be 160x6.

Not to bad to include in a feedees "diet".

I think that context might be of help here. Coca Cola (Classic) is fattening in comparison to water, but only if consumed in sufficient quantity so as to create caloric surplus.

It is high in sugar, even when compared to many other soft drinks, but like any type of food or drink, it's only "fattening" if you have enough of it.

So Coke is fattening because a lot of people will tend to drink sodas instead of water. In addition to the sugar and calories you ideally wouldn't be getting it also has caffeine that makes you want more and some salt that makes feel thirsty faster so you reach for another. As far as calorie density milk is better but Coke is empty calories designed to make you want more.

Another reason for sugar being fattening is that it messes with your metabolism and insulin levels. Sounds scary, but basically when there's excess sugar in your body, it temporary kicks up your bodies' calorie to fat reserve conversion rate. So sugar during and after meals increases the efficiency at which the meal is stored as fat, in addition to the calories of the sugar itself.

Anything is fattening if eaten or drunk in excess..except vegetables

Even vegetables, high starch vegetables in particular. I doubt it would be desirable or practically possible to create a calorie surplus with lettuce, however.

And you can drink all the water and sugar-free soft drinks you wish and they’ll not make you fat.