I used to be able to eat what I wanted and stay a size 10.
I did 50 minutes on the cross trainer at level 11, 60 rpm 4 or 5 times a week. 3 times a week I followed that with 15 mins weights and 100 sit ups.
This worked for 10 years!
Until the perimenopause started...My metabolism has changed hugely I think. I still do the exercise, but am size 14 and simply can't lose weight.
Of course I got very bored of the same routine, but the fact I was so slim and ate what I liked ( within reason- I had a healthy diet, lots of vegetables, not too much red meat, but could eat chocolate, cheese etc in moderation. Always had bread and pasta and wine though!)kept me motivated.
I now do a real mixture- lots of classes like Zumba and aerobics, fat burn as well as the crosstrainer.
I have a fit bit, and the highest calorie burn is from Zumba, then aeobics then crosstrainer, then country walk. Weight bearing classes like Fat burn and Pump burn the least, but are very good for you allegedly!