The unrealistic thing about this is how OTT the bullies are, but if you're reading this manga as someone who's just fat without an ED, then it's going to be off-putting. This is not a story of someone with normal day-to-day socially inflicted insecurity about their weight. Noko develops bulimia, which is an eating disorder. Actually, maybe you could criticize this manga as being too literally dictionary definition bulimia (my emphasis added): "an emotional disorder involving distortion of body image and an obsessive desire to lose weight, in which bouts of extreme overeating are followed by depression and self-induced vomiting, purging, or fasting."
From page one, we see something is emotionally wrong with Noko that is clearly being blamed on her weight. She fixates on her weight and consistently says "my life would be better if I was skinny." Noko also has some other things going on that feed into her issues surrounding her weight. For instance, extremely low self-esteem and a desperate need to feel loved...which likely caused her to seek out food as a comfort. We get some explanation of where this inferiority complex comes from.
We see glimpses that Noko only probably also needed just one good friend who was looking out for her. She reconnects to an old school friend that had an ideal body, but has put on weight & is generally ok, getting Noko to admit she stress eats and has been doing it for a while (since childhood). I think the author was trying to show here that Noko's stress eating differs from the average persons. I wish this old friend had stayed in the story, tbh because the people that "support" her from now on are creepy and either ambivalent or offer poor advice (Fujimoto, the john, and her batty "the reason you're fat is because of [a] disturbance in the lifewave" coworker Tabata).
By mid-point and after gradually losing weight and picking up an ED, these things are said by characters around Noko (the first one directly to her face and the other between two characters on the side):
"Nothing is going to change out of you losing weight." (- one of her co-workers to her directly)
"She'll probably repeat the cycle, because it's not about her body, really." (- the lady from the weight loss center, speaking to her assistant)
This is the point of this manga. Mayumi, the b*tch of a villain, who is thin & pretty & Noko aspires to be like, is miserable the whole time and that's obvious to the reader. The lady from the weight loss center goes on to say "it's her heart that's fat" -- which is a shitty thing to say (fatphobic, really) but I think the author meant that the thing that is making Noko so depressed isn't "fat", it's her own perception of herself that has nothing to do with fat. Unlike other mangas that feature weight loss, Noko's life is NOT better after losing weight. She sees "ugly" women discussing their love life in the bathroom and mentally derides them, eventually asking "So what allows them to act like they're all that?" Then in a hilarious effort, she insults them out loud and skips off happily...while the two women in the bathroom kind of go "lol wtf?? was she talking about herself or something?"
Skinny Noko's sad internal dialogue is "I'm stronger! I'm skinny! I'm okay!" and the author always juxtaposes it with her actual real life being an unhappy mess still. She's still compulsively over-eating anytime she's confronted with emotional stress, but now she has her self-destructive weapon of throwing it back up. Things come to a head when she sees her shitty ex with his fiance: "I have to eat and eat to become stronger. You can't lose...to reality. To reality. To reality."
Then finally she admits: "I haven't been able to become happy at all."
No one in this manga is happy -- not the random co-workers around her, not the beautiful bitch, not the crappy boyfriend, not Tabata. This is made very clear. However, the only one who has realized they are unhappy is Noko. This is her light at the end of the tunnel, this is how she "won." Yeah, the mega-assholes don't get their comeuppance but why do we care? They're gonna stay miserable and ultimately, joy should be derived from the self, not other people and their suffering (this is a big theme with her boyfriend and the villain b*tch.)
To me, this isn't a manga about the values of weight loss. It's abundantly clear that if Noko had just accepted her body and not listened to everyone who told her she needed to "lose weight" or "gain weight" (her ex and Fujimoto mainly) and made choices on her own accord, she'd be happy -- whether she decided to lose weight or stay as she was. This is a manga about an eating disorder. It doesn't have a happy ending. We do hear a nurse tell Noko to "chew her food properly" and "avoid extreme diets" as well as get the impression that Noko knows that she has bigger problems than her weight. But recovery from an ED is not linear and you cannot wrap it in a neat bow -- Noko's path to recovery is just starting. Recovery doesn't mean being fat or being skinny -- it's about fixing one's relationship with food and being healthy (a nebulous concept but Noko is not healthy at the end) and most importantly, happy in your skin.
Some bit are clumsy, it's kind of dramatic, some of the plot happenings are contrived, and the author seemed to want to do more with the lady from the weight loss center so she was an oddball character even though she serves her purpose. Overall, it tackles a heavy topic and has a message that isn't glorifying anything nor is it condemning anything. You end this manga feeling bad for Noko and wishing her the best, hoping she doesn't fall back into the toxic cycle of purging but also doesn't fall back into the toxic cycle of trying to derive validation from people who don't care about her at all.
edit: To respond to the person who suggested Cousin as an alternative to this...Tsubomi (the main character in Cousin) does NOT have an eating disorder. Cousin is one of my favorite mangas and I recommend it as a realistic depiction of the struggles of cyclic weight loss but Tsubomi just diets as someone else would & her self-esteem fluctuates but she's never super down on herself. Cousin is very uplifting & refreshing but it's not about an ED. As for Bara no Tame ni...that's a dramatic manga and I guess it's comparable to this, but I wouldn't say it's better? The main theme isn't really about ED and it's also a "ugly girl who everyone grows to like and turns out to be very pretty" kind of story....which isn't really what's happening here. Not all stories about weight loss and self-image are tackling the same things...