It can be difficult for some people to lose chest fat. No matter how much weight is lost from the body as a whole, the chest fat appears to remain. Some people have gynecomastia, which is an abnormal number of glands under the nipples that attract fat accumulation.
The recommendation is to maintain a low body fat percentage for people like the ones mentioned above, as well as anyone who wants to lose chest fat (18 percent or so). The Keto diet is the best diet for this: