Thinking about the first part of Naruto, among all the strong kunoichi such as, for example, Kurenai, Tsunade, Temari etc, one of them in particular was a very badass character: Anko.
Although in that period she was a really good looking woman, at a certain point she disappeared from the main events and we found her again in the Boruto series after a very long time; the biggest difference from the past is that now she’s no more a beautiful girl and, on the contrary, it looks like she has joined the Akimichi Clan.
How is it possible that she gained so much weight?
Well, to begin with we have to remember that Anko made her first appearance as an examiner of the second part of the chunin exam; moreover, during a filler, we came to know that, as a genin, she was a member of Orochimaru’s team alongside with Kabuto’s master and a Hyuga Clan member. In that period, she received and survived to Orochimaru’s cursed mark but, in the end, she decided not to follow him because she didn’t like his sensei’s aims, so that Orochimaru decided to cancel her memory in order to avoid her to reveal something about his plans; anyway, despite she gave up with Orochimaru’s teachings, she learnt a lot of incredible techniques, such as using snakes to fight and kill people.
Secondly, her name “Anko” reminds of “dango”, that is the typical japanese sweet that she usually loves eating, and her surname “Mitarashi” is a particular kind of dango; in fact, during the Naruto series, we can very often see her eating a lot of sweets and, in particular, dangos, for a total amount of about 18.000 calories per day.
Now, if we put together the facts that she’s completely addicted to food, that she follows a wrong diet and that, since after the Fourth Great Shinobi War came a peaceful period, Anko didn’t even have the occasion to go on a mission no more and in this way keep her body in shape, we can easily understand how her incredible change is probably due to a former change in her lifestyle and in her habits.
In addition, considering the fact that only one person over ten can survive to Orochimaru’s cursed mark, this means that it is a very powerful jutsu which is difficult for the body to bear, so maybe Anko’s fattening is also due to it and to the fact that apparently after the Fourth Great Shinobi War her cursed mark has been removed, so we can imagine that it has been a difficult operation which hard-tested her body.