英国这边的话,会说big, large, plump,big boned, 不会直接说fat,不礼貌。
The man is plump / big.
瘦,有很多种说法,一般是说slim,slender 苗条的瘦,bony/boney,就是表示非常瘦了,很骨感了。这个具体用什么,是看你具体是想形容哪种瘦。
She is pretty, but too boney. It would be much better if she could put some weight.
You look mucher bigger /slimmer than before.
That man is a little fat.
She is beautiful but is too thin.it would be
better if she was more plump.
It seems that you look more chubbier / thiner
than before.