Body Building and weight loss

Patient: I am 37 year old Man,B+ve blood group, 174 cm H, 82 kg. I joined gym 7 months back and am almost regular in work outs, do aerobics once in week. My question is i am not able to loose weight, though i feel healthy and fit, major concern is my abs , where i don’t see any changes, what could be the reason for that? I recently read an article about food to avoid for B group individuals and they say chicken and nuts to avoid, i started avoiding that, is that the reason? please clarifyThanks