After being on this site for about two weeks now, I've noticed a trend. Nearly every protagonist (and side character, and villain, etc.) in everyone's fictional worlds are all… nearly underweight and white. Before I get into this, I have to commend you all. I've seen a lot of LGBT+ representation, people with disabilities or mental illnesses, etc. You've got that down.
However…
Not everyone in the world is white. Not everyone is an athletic blonde with blue eyes or a lithe red-head with green eyes and a smattering of freckles. Some people look different than that. And they'd like to be heroes for once. They'd like to see themselves in fiction, too! It's both boring and unrealistic to not include nonwhite, overweight or even just average weight protagonists. It's easier for readers everywhere to connect with characters who aren't all the exact same. I've seen many different personalities, different species, different everything! Except weight and race. It's important to represent others that look different from you. They exists. They're out there. And they should be here, too.
"But random girl!" you might say. "It's not unrealistic because…" And I'm going to stop you right there. If all your main characters are white, then it's unrealistic. If all your characters are skinny, unless its a post-apocalyptic society or everyone is starving for a good reason, then it's unrealistic. Point blank period.
TL; DR: Branch out! There's a whole world full of different races and cultures and peoples and it's vibrant! It's rich! Explore it. Use it.
You're a writer. Own it! Tell everyone's story.