textbooks are so wrong about 腹部

ok my textbook says 腹部 is only for like medical files but actually it's way more basic. in french we use 'abdomen' casually and japanese is the same. 腹 is belly and 部 is part. so it's literally 'belly part'. i always tell people my 腹部 hurts when i eat too much and they get it. people who say it's too formal just don't get linguistic roots. it's not that deep.