“Oompa Loompa, do-ba-dee-doo, I’ve got a perfect puzzle for you:” How many calories are in a Whopper; Big Mac or six-inch, veggie Subway sandwich? As a unit of measure, Americans are as clueless about the calorie as they are the kilogram in terms of judging amount. A study in the British Medical Journal found two-thirds of participants underestimated the calorie content of their fast-food meal, with 25 percent underestimating by at least 500 calories. Subway was most likely to confuse calorie-counters — most of its six-inch sandwiches fall between 350 and 500 calories (a Big Mac is 700 calories). Do-ba-dee-doo.