It seems like there are all sorts of non-scientific ways to estimate how many calories your body needs in a day (i.e. take your weight and multiply it times elven--or was it ten...). Knowing this can really help you plan a weight loss program (all you have to do is take the number of calories your body current needs to maintain its weight and subtract a few, right?), but everyone's metabolism is a bit different, depending on muscle mass and lots of other factors, so you really can't get a good idea by just using some hokey formula. That's why I like the idea of the Body Gem.
It's a little gadget where all you do is breathe into it, and it can measure the rate at which your body burns calories. With this information a physical trainer or dietician can help you plan a weight loss program that makes sense and will actually help get the pounds off.