I feel like the messaging in this is pretty nasty (albeit not entirely unexpected), as if her being overweight is the most significant thing about her. The "current weight = xx kg" tag at the end of each chapter really drives the feeling of unhealthy obsession with weight home, and the way she approached weight-loss near the beginning is downright anorexic (it's sort of not covered much thereafter). But the manga(ka?) thinks this is all good and admirable, it seems.
I mean, that's all in-character for Japan, inveterate fat-shaming society that it is, so not exactly surprising, but it's still a bit awful.
Other than that, it's a fun read.
(It should be noted I don't really have an objection to the way the people in the manga act, their various cruelties and insecurities on the subject seem about right; rather it's how the author frames it—which things are casually presented as "bad" and "good" and/or "justified"—that raises my hackles.)