My man, no one is becoming fat because they eat too many oranges for the vitamin C.

I'd strongly argue against that. A lot of people somewhat mindlessly consumer fruit and fruit juice 'because it's good for you' which is a reasonable proxy for high levels of things like Vitamin C.

And fruit is in general very good for you, but of course it's also quite high in calories. A single navel orange has upwards of 70 calories [1]. So 2 oranges ~= 1 can of Coke. And fruit juice is even worse. A plain cup of orange juice has 112 calories. If somebody buys some form of it that's been sweetened or otherwise mixed, you can easily end up with your OJ having more calories than a Coke.

People can easily speed their way to obesity by eating things that they think (and are) 'good for them' without really appreciating how many calories they're consuming. Similar to how things like vegans can easily end up consuming way too many calories when doing things like using peanuts as a protein source. An 80kg man needs around 64 grams of protein a day. 64 grams of protein from peanuts (to take things to an extreme) would be more than 1400 calories. And that's from raw unseasoned peanuts, which have the best nutrition:calorie ratio.

[1] - https://www.verywellfit.com/oranges-nutrition-facts-calories...

All other things being equal, eating more oranges (even salad) can very much result in being fatter.

Roughly speaking, 100 extra calories a day means 1 added pound of fat per month.

Yet, give it 100 years and see what’s going on.