Pete, without sounding controversial (and this came from a jewish physician)
......................people of all ages, shapes and sizes, overactive or underactive thyroids, vegetarians, sporty people, lazy people, fat people, thin people, ill people, healthy people etc etc etc etc were forced in to concentration camps in WW2.
When they came out (if fortune favoured them) the one thing they had in common was they were all skinny. The spirits and minds were of varying degrees but all the bodie were skinny...........................
History has proved that starvation makes you thin.
I would never advocate starvation, but the equation is simple. Burn more off than you eat.
I would go further, and completely ignore calories. They are so eighties and mean nothing in the real world.
Just eat good calories, fruits, veggies, nuts, milk, lean meat, wholemeal foods etc. Do not worry about these harpies who say "Ooooh bananas have loads of sugars in them" "Ooooooh nuts are full of fat"...utter tosh.
Cut out the cr4p completely. And I mean completely if you are dieting.
Trust me, I am the self-appointed fittest anti-diet, anti-gym health guru on AB.
One further point, think incentive. What has the most incentive, being fit and healthy and living longer to see you kids/grandchildren or a KFC???
Good luck, you can do it.