When I was doing some research for a story about why people are always in other people's business I came across several mainstream health-related websites that make it clear that although weight can be correlated with health, it isn't necessarily. Things like cholesterol levels and BP rates are much more important that BMI and there are also plenty of "thin" people who have issues with these things who are actually less healthy than larger folks. When I wrote about this in the story, complete with links, I still got all sorts of people wanting to argue with me because "everyone knows...." The thing with everyone knows is that it's nearly always wrong. The fact that so many doctors are still clinging to the outdated "everyone knows" narrative is really disturbing.

https://www.webmd.com/diet/obesity/news/20160204/obese-may-not-always-equal-unhealthy-study#1

Using a government health survey, researchers found that nearly half of overweight U.S. adults were "metabolically healthy."

"The bigger picture we want to draw from our findings is that the dominant way of thinking about weight -- that higher-weight individuals will always be unhealthy -- is flawed," said Jeffrey Hunger, one of the researchers on the study and a doctoral candidate at the University of California, Santa Barbara.