This article has lots of good data, showing the BMI levels of patients with anorexia nervosa, at diagnosis, and at long term follow-up throughout their adult lives.
I’ve referenced this article because it has a chart showing the BMI percentiles of the German population, using data from the German National Nutrition Survey, 1985-1989. (It was a big survey of 21,452 German citizens.)
As with all other populations that I’ve seen, Germans also show an increasing body mass index (BMI) during their adult lives.
For the benefit of people searching for articles about BMI in anorexia nervosa, this article showed these charts. Notice that the BMI values of anorexia nervosa were mostly well below the 3rd percentile ( at diagnosis). Then after follow-up 10 years later, most patients had recovered into the low-normal BMI range, but very few patients exceeded the 50th percentile.