Just record everything you eat, if you can, record the calorie intake.

record the calorie you burn from workout

use 2000 calorie/day (depending on your gender, etc) as balance point.

count calorie deficit, 3500 cal= 1 pound. You will find it is relatively accurate. I did that myself, the correlation is excellent.

It does not depend much on what you eat, it is just simple energy conservation.