remember the sit ups and your core good benefits from that , and i think if you done weights you would lose weight untill you started to put muscle on then it would go up .
i train for around an hour 3 times a week sometimes doing boxing training , press ups, sit ups on the days i dont do weights altho this is only now and agein but i am not looking to lose weight as i do a manuel job and work like mad so this helps i think