they can tell until the cows come home but it's very hard to actually do it cause most causes are environmental and lifestyle related that can't easily be changed - can't all of a sudden start walking to work if you live in a car dependent area and that's true for most of the USA.

Wake me up when you find a US government with the guts to mandate cuts in the amount of high fructose corn syrup allowed in staple foods, put a tax on sugary drinks etc...

until then telling people to lose weight is a waste of time.